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Schedule III - Real Estate Assets and Accumulated Depreciation (Details) (USD $)
 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2012
EYE STREET 1225 [Member]
Dec. 31, 2012
EYE STREET 1201 [Member]
Dec. 31, 2011
Interlocken Building 360 [Member]
Dec. 31, 2011
Interlocken Building 360 [Member]
Fund IX, X, XI and REIT Joint Venture [Member]
Dec. 31, 2012
Secured Debt [Member]
$350.0 Million Secured Pooled Facility [Member]
Dec. 31, 2012
Eye Street 1225 NW Associates LLC [Member]
Dec. 31, 2012
Eye Street 1225 NW Associates LLC [Member]
1225 Equity LLC [Member]
Dec. 31, 2012
Eye Street 1201 NW Associates LLC [Member]
Dec. 31, 2012
Eye Street 1201 NW Associates LLC [Member]
1201 Equity LLC [Member]
Dec. 31, 2012
Building Improvements [Member]
Minimum [Member]
Dec. 31, 2012
Building Improvements [Member]
Maximum [Member]
Dec. 31, 2012
Land Improvements [Member]
Minimum [Member]
Dec. 31, 2012
Land Improvements [Member]
Maximum [Member]
Dec. 31, 2012
Building [Member]
Dec. 31, 2012
Wholly Owned Properties [Member]
Dec. 31, 2012
Partially Owned Properties [Member]
Dec. 31, 2012
Partially Owned Properties [Member]
Building 2020 [Member]
Dec. 31, 2012
Partially Owned Properties [Member]
Building 2020 [Member]
Minimum [Member]
Dec. 31, 2012
Partially Owned Properties [Member]
Building 2020 [Member]
Maximum [Member]
Dec. 31, 2012
Partially Owned Properties [Member]
INVESTMENT DRIVE 4685 [Member]
Dec. 31, 2012
Partially Owned Properties [Member]
INVESTMENT DRIVE 4685 [Member]
Minimum [Member]
Dec. 31, 2012
Partially Owned Properties [Member]
INVESTMENT DRIVE 4685 [Member]
Maximum [Member]
Dec. 31, 2012
Partially Owned Properties [Member]
MARYLAND WAY 5301 [Member]
Dec. 31, 2012
Partially Owned Properties [Member]
MARYLAND WAY 5301 [Member]
Minimum [Member]
Dec. 31, 2012
Partially Owned Properties [Member]
MARYLAND WAY 5301 [Member]
Maximum [Member]
Dec. 31, 2012
Partially Owned Properties [Member]
UPLAND DRIVE 8560 [Member]
Dec. 31, 2012
Partially Owned Properties [Member]
UPLAND DRIVE 8560 [Member]
Minimum [Member]
Dec. 31, 2012
Partially Owned Properties [Member]
UPLAND DRIVE 8560 [Member]
Maximum [Member]
Dec. 31, 2012
Partially Owned Properties [Member]
TWO PARK CENTER [Member]
Dec. 31, 2012
Partially Owned Properties [Member]
TWO PARK CENTER [Member]
Minimum [Member]
Dec. 31, 2012
Partially Owned Properties [Member]
TWO PARK CENTER [Member]
Maximum [Member]
May 31, 2010
Sylvan Avenue 111 Building [Member]
Dec. 31, 2012
Held-for-Sale Real Estate Properties [Member]
Wholly Owned Properties [Member]
Dec. 31, 2012
Held-for-Sale Real Estate Properties [Member]
Wholly Owned Properties [Member]
1111 DURHAM AVENUE [Member]
Dec. 31, 2012
Held-for-Sale Real Estate Properties [Member]
Wholly Owned Properties [Member]
1111 DURHAM AVENUE [Member]
Minimum [Member]
Dec. 31, 2012
Held-for-Sale Real Estate Properties [Member]
Wholly Owned Properties [Member]
1111 DURHAM AVENUE [Member]
Maximum [Member]
Dec. 31, 2012
Held-for-Sale Real Estate Properties [Member]
Wholly Owned Properties [Member]
ENCLAVE PARKWAY 1200 [Member]
Dec. 31, 2012
Held-for-Sale Real Estate Properties [Member]
Wholly Owned Properties [Member]
ENCLAVE PARKWAY 1200 [Member]
Minimum [Member]
Dec. 31, 2012
Held-for-Sale Real Estate Properties [Member]
Wholly Owned Properties [Member]
ENCLAVE PARKWAY 1200 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
DALLAS PARKWAY 3900 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
DALLAS PARKWAY 3900 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
DALLAS PARKWAY 3900 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
RIVER CORPORATE CENTER [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
RIVER CORPORATE CENTER [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
RIVER CORPORATE CENTER [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
SOUTH PRICE ROAD 8700 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
SOUTH PRICE ROAD 8700 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
SOUTH PRICE ROAD 8700 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
1441 WEST LONG LAKE ROAD [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
1441 WEST LONG LAKE ROAD [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
1441 WEST LONG LAKE ROAD [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
ENCLAVE PARKWAY 1430 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
ENCLAVE PARKWAY 1430 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
ENCLAVE PARKWAY 1430 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CRESCENT RIDGE II [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CRESCENT RIDGE II [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CRESCENT RIDGE II [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CROWN COLONY DRIVE 1200 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CROWN COLONY DRIVE 1200 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CROWN COLONY DRIVE 1200 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
HIATUS ROAD 5601 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
HIATUS ROAD 5601 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
HIATUS ROAD 5601 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
WINDY POINT I [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
WINDY POINT I [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
WINDY POINT I [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
WINDY POINT II [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
WINDY POINT II [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
WINDY POINT II [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
SARASOTA COMMERCE CENTER II [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
SARASOTA COMMERCE CENTER II [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
SARASOTA COMMERCE CENTER II [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
JOHNS CREEK PARKWAY 11695 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
JOHNS CREEK PARKWAY 11695 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
JOHNS CREEK PARKWAY 11695 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
BROOKSIDE PARKWAY 3750 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
BROOKSIDE PARKWAY 3750 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
BROOKSIDE PARKWAY 3750 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
NW 64TH STREET 2001 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
NW 64TH STREET 2001 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
NW 64TH STREET 2001 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CENTRAL STREET 90 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CENTRAL STREET 90 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CENTRAL STREET 90 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
DESERT CANYON 300 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
DESERT CANYON 300 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
DESERT CANYON 300 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CONNECTION DRIVE 6031 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CONNECTION DRIVE 6031 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CONNECTION DRIVE 6031 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CONNECTION DRIVE 6021 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CONNECTION DRIVE 6021 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CONNECTION DRIVE 6021 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CONNECTION DRIVE 6011 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CONNECTION DRIVE 6011 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CONNECTION DRIVE 6011 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
BRAKER POINTE III [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
BRAKER POINTE III [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
BRAKER POINTE III [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CHANDLER FORUM [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CHANDLER FORUM [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CHANDLER FORUM [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
GATEHALL DRIVE 2 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
GATEHALL DRIVE 2 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
GATEHALL DRIVE 2 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
SPECTRUM LOOP 350 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
SPECTRUM LOOP 350 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
SPECTRUM LOOP 350 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
HEADQUARTERS DRIVE 5601 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
HEADQUARTERS DRIVE 5601 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
HEADQUARTERS DRIVE 5601 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
TWO INDEPENDENCE SQUARE [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
TWO INDEPENDENCE SQUARE [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
TWO INDEPENDENCE SQUARE [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
ONE INDEPENDENCE SQUARE [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
ONE INDEPENDENCE SQUARE [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
ONE INDEPENDENCE SQUARE [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
WEST END AVENUE 2120 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
WEST END AVENUE 2120 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
WEST END AVENUE 2120 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
NORTH BRAND BOULEVARD 800 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
NORTH BRAND BOULEVARD 800 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
NORTH BRAND BOULEVARD 800 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
EASTPOINT I [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
EASTPOINT I [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
EASTPOINT I [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
EASTPOINT II [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
EASTPOINT II [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
EASTPOINT II [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
WEST JEFFERSON 150 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
WEST JEFFERSON 150 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
WEST JEFFERSON 150 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
US BANCORP CENTER [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
US BANCORP CENTER [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
US BANCORP CENTER [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
AON CENTER [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
AON CENTER [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
AON CENTER [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
AUBURN HILLS CORPORATE CENTER [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
AUBURN HILLS CORPORATE CENTER [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
AUBURN HILLS CORPORATE CENTER [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
SUNSET HILLS ROAD 11107 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
SUNSET HILLS ROAD 11107 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
SUNSET HILLS ROAD 11107 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
SUNSET HILLS ROAD 11109 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
SUNSET HILLS ROAD 11109 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
SUNSET HILLS ROAD 11109 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CORPORATE BOULEVARD 9211 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CORPORATE BOULEVARD 9211 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CORPORATE BOULEVARD 9211 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CORPORATE BOULEVARD 9221 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CORPORATE BOULEVARD 9221 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CORPORATE BOULEVARD 9221 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
GLENRIDGE HIGHLANDS TWO [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
GLENRIDGE HIGHLANDS TWO [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
GLENRIDGE HIGHLANDS TWO [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
BRIDGEWATER CROSSING 200 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
BRIDGEWATER CROSSING 200 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
BRIDGEWATER CROSSING 200 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
EAST COLORADO BOULEVARD 1055 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
EAST COLORADO BOULEVARD 1055 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
EAST COLORADO BOULEVARD 1055 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
FAIRWAY CENTER II [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
FAIRWAY CENTER II [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
FAIRWAY CENTER II [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
COPPER RIDGE CENTER [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
COPPER RIDGE CENTER [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
COPPER RIDGE CENTER [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
MAIN STREET 1901 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
MAIN STREET 1901 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
MAIN STREET 1901 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
VIRGINIA AVE 400 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
VIRGINIA AVE 400 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
VIRGINIA AVE 400 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
NORTH FAIRFAX DRIVE 4250 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
NORTH FAIRFAX DRIVE 4250 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
NORTH FAIRFAX DRIVE 4250 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
EYE STREET 1225 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
EYE STREET 1225 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
EYE STREET 1225 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
EYE STREET 1201 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
EYE STREET 1201 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
EYE STREET 1201 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
MARKET STREET 1901 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
MARKET STREET 1901 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
MARKET STREET 1901 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
BROAD STREET 60 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
BROAD STREET 60 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
BROAD STREET 60 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
MASSACHUSETTS AVENUE 1414 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
MASSACHUSETTS AVENUE 1414 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
MASSACHUSETTS AVENUE 1414 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
ONE BRATTLE SQUARE [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
ONE BRATTLE SQUARE [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
ONE BRATTLE SQUARE [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CORPORATE DRIVE 600 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CORPORATE DRIVE 600 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CORPORATE DRIVE 600 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
WEST ENTRANCE DRIVE 1075 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
WEST ENTRANCE DRIVE 1075 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
WEST ENTRANCE DRIVE 1075 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CLARENDON BOULEVARD 3100 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CLARENDON BOULEVARD 3100 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CLARENDON BOULEVARD 3100 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CORPORATE BOULEVARD 9200 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CORPORATE BOULEVARD 9200 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CORPORATE BOULEVARD 9200 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
BRIDGEWATER CROSSING 400 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
BRIDGEWATER CROSSING 400 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
BRIDGEWATER CROSSING 400 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
LAS COLINAS CORPORATE CENTER I [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
LAS COLINAS CORPORATE CENTER I [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
LAS COLINAS CORPORATE CENTER I [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
LAS COLINAS CORPORATE CENTER II [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
LAS COLINAS CORPORATE CENTER II [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
LAS COLINAS CORPORATE CENTER II [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
TWO PIERCE PLACE [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
TWO PIERCE PLACE [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
TWO PIERCE PLACE [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CABOT DRIVE 2300 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CABOT DRIVE 2300 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
CABOT DRIVE 2300 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
PIEDMONT POINTE I [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
PIEDMONT POINTE I [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
PIEDMONT POINTE I [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
PIEDMONT POINTE II [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
PIEDMONT POINTE II [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
PIEDMONT POINTE II [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
SUWANEE GATEWAY ONE [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
SUWANEE GATEWAY ONE [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
SUWANEE GATEWAY ONE [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
ONE MERIDIAN CROSSINGS [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
ONE MERIDIAN CROSSINGS [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
ONE MERIDIAN CROSSINGS [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
TWO MERIDIAN CROSSINGS [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
TWO MERIDIAN CROSSINGS [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
TWO MERIDIAN CROSSINGS [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
W MONROE 500 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
W MONROE 500 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
W MONROE 500 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
THE DUPREE [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
THE DUPREE [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
THE DUPREE [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
THE MEDICI [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
THE MEDICI [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
THE MEDICI [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
PRESIDENTIAL WAY 225 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
PRESIDENTIAL WAY 225 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
PRESIDENTIAL WAY 225 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
PRESIDENTIAL WAY 235 [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
PRESIDENTIAL WAY 235 [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
PRESIDENTIAL WAY 235 [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
400 TOWNPARK [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
400 TOWNPARK [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
400 TOWNPARK [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
PIEDMONT POWER, LLC [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
PIEDMONT POWER, LLC [Member]
Minimum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
PIEDMONT POWER, LLC [Member]
Maximum [Member]
Dec. 31, 2012
Operating Real Estate Properties [Member]
Wholly Owned Properties [Member]
UNDEVELOPED LAND PARCELS [Member]
Real Estate and Accumulated Depreciation [Line Items]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
Ownership Percentage       49.50% 49.50%                             57.00%     55.00%     55.00%     72.00%     72.00%         100.00% [1]     100.00% [1]       100.00%     100.00% [2]     100.00% [2]     100.00%     100.00%     100.00%     100.00% [3]     100.00%     100.00%     100.00%     100.00%     100.00%     100.00%     100.00% [2]     100.00%     100.00%     100.00%     100.00%     100.00%     100.00% [3]     100.00%     100.00% [3]     100.00%     100.00%     100.00% [3]     100.00% [3]     100.00% [3]     100.00%     100.00%     100.00%     100.00%     100.00%     100.00%     100.00%     100.00%     100.00%     100.00%     100.00%     100.00%     100.00% [3]     100.00%     100.00% [3]     100.00%     100.00%     100.00%     100.00%     49.50% [4]     49.50% [5]     100.00%     100.00%     100.00%     100.00%     100.00%     100.00%     100.00%     100.00%     100.00% [3]     100.00%     100.00%     100.00%     100.00%     100.00%     100.00%     100.00%     100.00%     100.00%     100.00%     100.00%     100.00%     100.00%     100.00%     100.00%     100.00% [6]     100.00% [7]
Encumbrances                                                                                                               $ 32,100,000           $ 20,200,000 [3]           $ 23,400,000     $ 40,300,000                                                           $ 16,500,000 [3]           $ 42,700,000 [3]                 $ 105,800,000 [3]     $ 57,800,000 [3]     $ 26,800,000 [3]                             $ 105,000,000     $ 225,000,000                                         $ 40,200,000 [3]     $ 29,200,000     $ 10,700,000 [3]                       $ 45,000,000     $ 57,600,000 [4]     $ 82,400,000 [5]                                                     $ 29,300,000 [3]     $ 17,500,000     $ 25,025,000                                               $ 140,000,000                                          
Initial Cost, Land 610,371,000                                 599,677,000 10,694,000 1,696,000     2,144,000     4,300,000     1,954,000     600,000       13,113,000 9,653,000 [1]     3,460,000 [1]     586,564,000 1,456,000     0 [2]     0 [2]     2,160,000     7,100,000     7,700,000     11,042,000 [3]     3,642,000     4,537,000     3,746,000     1,767,000     2,080,000     1,561,000     0 [2]     3,642,000     2,602,000     3,157,000     3,157,000     3,157,000     6,098,000 [3]     2,632,000     9,054,000 [3]     2,185,000     3,153,000     52,711,000 [3]     29,765,000 [3]     4,908,000 [3]     23,605,000     1,485,000     1,235,000     9,759,000     11,138,000     23,267,000     1,978,000     2,711,000     1,218,000     3,019,000     3,019,000     6,662,000     8,182,000 [3]     6,495,000     7,110,000 [3]     6,974,000     6,246,000     22,146,000     13,636,000     21,959,000 [4]     31,985,000 [5]     13,584,000     32,522,000     4,210,000     6,974,000     3,934,000     5,200,000     11,700,000     3,730,000     10,400,000 [3]     3,912,000     4,496,000     4,370,000     4,390,000     11,200,000     13,300,000     1,000,000     2,919,000     2,661,000     36,990,000     4,080,000     1,780,000     3,626,000     4,154,000     2,570,000     0 [6]     6,021,000 [7]
Initial Cost, Buildings and Improvements 3,907,382,000                                 3,834,947,000 72,435,000 7,851,000     9,984,000     20,702,000     11,216,000     22,682,000       35,542,000 20,495,000 [1]     15,047,000 [1]     3,799,405,000 20,377,000     16,036,000 [2]     13,272,000 [2]     16,776,000     37,915,000     45,154,000     40,666,000 [3]     10,404,000     31,847,000     55,026,000     20,533,000     13,572,000     14,207,000     7,172,000 [2]     29,497,000     24,333,000     43,656,000     42,662,000     29,034,000     34,492,000 [3]     0     96,722,000 [3]     24,964,000     24,602,000     202,702,000 [3]     104,814,000 [3]     59,011,000 [3]     136,284,000     11,064,000     9,199,000     88,364,000     175,629,000     472,488,000     16,570,000     17,890,000     8,038,000     21,984,000     21,984,000     69,031,000     84,160,000 [3]     30,265,000     15,600,000 [3]     38,714,000     36,455,000     49,740,000     70,918,000     47,602,000 [4]     63,139,000 [5]     166,683,000     168,986,000     35,821,000     64,940,000     0     22,957,000     69,705,000     16,608,000     71,052,000 [3]     18,830,000     29,881,000     70,632,000     19,549,000     58,606,000     70,618,000     6,875,000     24,398,000     25,742,000     185,113,000     14,310,000     11,510,000     36,916,000     44,048,000     20,555,000     79,000 [6]     427,000 [7]
Initial Cost, Total 4,517,753,000                                 4,434,624,000 83,129,000 9,547,000     12,128,000     25,002,000     13,170,000     23,282,000       48,655,000 30,148,000 [1]     18,507,000 [1]     4,385,969,000 21,837,000     16,036,000 [2]     13,272,000 [2]     18,936,000     45,015,000     52,854,000     51,708,000 [3]     14,046,000     36,384,000     58,772,000     22,300,000     15,652,000     15,768,000     7,172,000 [2]     33,139,000     26,935,000     46,813,000     45,819,000     32,191,000     40,590,000 [3]     2,632,000     105,776,000 [3]     27,149,000     27,755,000     255,413,000 [3]     134,579,000 [3]     63,919,000 [3]     159,889,000     12,549,000     10,434,000     98,123,000     186,767,000     495,755,000     18,548,000     20,601,000     9,256,000     25,003,000     25,003,000     75,693,000     92,342,000 [3]     36,760,000     22,710,000 [3]     45,688,000     42,701,000     71,886,000     84,554,000     69,561,000 [4]     95,124,000 [5]     180,267,000     201,508,000     40,031,000     71,914,000     3,934,000     28,157,000     81,405,000     20,338,000     81,452,000 [3]     22,742,000     34,377,000     75,002,000     23,939,000     69,806,000     83,918,000     7,875,000     27,317,000     28,403,000     222,103,000     18,390,000     13,290,000     40,542,000     48,202,000     23,125,000     79,000 [6]     6,448,000 [7]
Costs Capitalized Subsequent to Acquisition 131,147,000                                 130,001,000 1,146,000 (1,259,000)     2,902,000     1,360,000     1,084,000     (2,941,000)       (5,358,000) (11,547,000) [1]     6,189,000 [1]     135,359,000 3,047,000     7,309,000 [2]     551,000 [2]     (6,760,000)     3,700,000     7,954,000     1,970,000 [3]     1,722,000     2,341,000     1,096,000     2,249,000     1,648,000     112,000     769,000 [2]     2,630,000     100,000     2,419,000     1,397,000     2,586,000     1,000 [3]     19,917,000     33,000 [3]     (1,894,000)     2,663,000     21,374,000 [3]     2,770,000 [3]     6,671,000 [3]     8,900,000     423,000     1,895,000     3,846,000     7,614,000     125,542,000     (8,159,000)     1,371,000     (2,338,000)     (4,844,000)     (4,822,000)     (22,036,000)     (17,783,000) [3]     (8,338,000)     (2,298,000) [3]     (5,675,000)     (5,019,000)     (1,856,000)     5,098,000     (2,559,000) [4]     (3,133,000) [5]     137,000     (5,994,000)     1,988,000     (3,814,000)     16,281,000     (313,000)     (5,363,000)     (1,624,000)     (8,218,000) [3]     (2,279,000)     (7,083,000)     1,667,000     (2,849,000)     7,339,000     6,279,000     78,000     (1,000)     99,000     (20,929,000)     55,000     728,000     (764,000)     (911,000)     580,000     3,079,000 [6]     2,987,000 [7]
Gross Amount at Which Carried, Land 640,687,000                                 629,536,000 11,151,000 1,767,000     2,233,000     4,479,000     2,048,000     624,000       7,188,000 3,728,000 [1]     3,460,000 [1]     622,348,000 1,517,000     0 [2]     0 [2]     1,202,000     5,506,000     8,021,000     11,042,000 [3]     3,642,000     4,537,000     3,746,000     2,203,000     2,081,000     1,561,000     0 [2]     3,642,000     2,602,000     3,157,000     3,157,000     3,157,000     6,099,000 [3]     2,779,000     9,054,000 [3]     2,186,000     3,153,000     52,711,000 [3]     30,562,000 [3]     5,100,000 [3]     23,607,000     1,485,000     1,235,000     9,759,000     11,138,000     23,966,000     1,591,000     2,711,000     1,218,000     2,960,000     2,960,000     6,662,000     8,328,000 [3]     6,495,000     7,110,000 [3]     6,974,000     6,246,000     22,146,000     13,636,000     21,959,000 [4]     31,985,000 [5]     20,829,000     60,708,000     4,365,000     7,113,000     3,934,000     5,207,000     11,791,000     3,882,000     10,400,000 [3]     2,543,000     2,543,000     4,370,000     4,390,000     11,200,000     13,300,000     1,000,000     2,919,000     2,661,000     36,990,000     4,080,000     1,780,000     3,612,000     4,138,000     2,570,000     0 [6]     9,435,000 [7]
Gross Amount at Which Carried, Buildings and Improvements 4,008,217,000                                 3,935,093,000 73,124,000 6,521,000     12,797,000     21,883,000     12,206,000     19,717,000       36,109,000 14,873,000 [1]     21,236,000 [1]     3,898,984,000 23,367,000     23,345,000 [2]     13,823,000 [2]     10,974,000     43,209,000     52,787,000     42,636,000 [3]     12,126,000     34,188,000     56,122,000     22,346,000     15,219,000     14,319,000     7,941,000 [2]     32,127,000     24,433,000     46,075,000     44,059,000     31,620,000     34,492,000 [3]     19,770,000     96,755,000 [3]     23,069,000     27,265,000     224,076,000 [3]     106,787,000 [3]     65,490,000 [3]     145,182,000     11,487,000     11,094,000     92,210,000     183,243,000     597,331,000     8,798,000     19,261,000     5,700,000     17,199,000     17,221,000     46,995,000     66,231,000 [3]     21,927,000     13,302,000 [3]     33,039,000     31,436,000     47,884,000     76,016,000     45,043,000 [4]     60,006,000 [5]     159,575,000     134,806,000     37,654,000     60,987,000     16,281,000     22,637,000     64,251,000     14,832,000     62,834,000 [3]     17,920,000     24,751,000     72,299,000     16,700,000     65,945,000     76,897,000     6,953,000     24,397,000     25,841,000     164,184,000     14,365,000     12,238,000     36,166,000     43,153,000     21,135,000     3,158,000 [6]      
Gross Amount at Which Carried, Total 4,648,904,000                                 4,564,629,000 84,275,000 8,288,000     15,030,000     26,362,000     14,254,000     20,341,000       43,297,000 18,601,000 [1]     24,696,000 [1]     4,521,332,000 24,884,000     23,345,000 [2]     13,823,000 [2]     12,176,000     48,715,000     60,808,000     53,678,000 [3]     15,768,000     38,725,000     59,868,000     24,549,000     17,300,000     15,880,000     7,941,000 [2]     35,769,000     27,035,000     49,232,000     47,216,000     34,777,000     40,591,000 [3]     22,549,000     105,809,000 [3]     25,255,000     30,418,000     276,787,000 [3]     137,349,000 [3]     70,590,000 [3]     168,789,000     12,972,000     12,329,000     101,969,000     194,381,000     621,297,000     10,389,000     21,972,000     6,918,000     20,159,000     20,181,000     53,657,000     74,559,000 [3]     28,422,000     20,412,000 [3]     40,013,000     37,682,000     70,030,000     89,652,000     67,002,000 [4]     91,991,000 [5]     180,404,000     195,514,000     42,019,000     68,100,000     20,215,000     27,844,000     76,042,000     18,714,000     73,234,000 [3]     20,463,000     27,294,000     76,669,000     21,090,000     77,145,000     90,197,000     7,953,000     27,316,000     28,502,000     201,174,000     18,445,000     14,018,000     39,778,000     47,291,000     23,705,000     3,158,000 [6]     9,435,000 [7]
Accumulated Depreciation and Amortization 977,768,000 935,716,000 918,578,000                             951,897,000 25,871,000 3,906,000     6,029,000     7,242,000     3,612,000     5,082,000       9,327,000 8,378,000 [1]     949,000 [1]     942,570,000 8,826,000     6,291,000 [2]     4,902,000 [2]     6,766,000     14,686,000     19,404,000     13,020,000 [3]     3,404,000     10,157,000     16,575,000     6,732,000     4,695,000     4,189,000     2,177,000 [2]     9,799,000     6,906,000     12,465,000     12,756,000     9,395,000     9,544,000 [3]     6,334,000     26,514,000 [3]     6,313,000     6,797,000     55,720,000 [3]     28,479,000 [3]     17,776,000 [3]     39,209,000     2,972,000     3,155,000     25,154,000     46,382,000     143,225,000     3,763,000     4,901,000     1,490,000     4,186,000     4,194,000     11,536,000     14,672,000 [3]     5,494,000     3,003,000 [3]     8,408,000     8,681,000     11,467,000     21,922,000     11,262,000 [4]     13,985,000 [5]     44,068,000     33,533,000     13,114,000     23,204,000     4,561,000     4,694,000     12,864,000     2,987,000     15,093,000 [3]     6,527,000     4,591,000     16,258,000     4,640,000     8,407,000     8,670,000     405,000     1,550,000     1,824,000     8,565,000     1,067,000     777,000     2,038,000     2,421,000     1,029,000     0 [6]      
Life on which Depreciation and Amortization is Computed                                         0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]       0 years [1],[8] 40 years [1],[8]   0 years [1],[8] 40 years [1],[8]     0 years [8] 40 years [8]   0 years [2],[8] 40 years [2],[8]   0 years [2],[8] 40 years [2],[8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [3],[8] 40 years [3],[8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [2],[8] 40 years [2],[8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [3],[8] 40 years [3],[8]   0 years [8] 40 years [8]   0 years [3],[8] 40 years [3],[8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [3],[8] 40 years [3],[8]   0 years [3],[8] 40 years [3],[8]   0 years [3],[8] 40 years [3],[8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [3],[8] 40 years [3],[8]   0 years [8] 40 years [8]   0 years [3],[8] 40 years [3],[8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [4],[8] 40 years [4],[8]   0 years [5],[8] 40 years [5],[8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [3],[8] 40 years [3],[8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [8] 40 years [8]   0 years [6],[8] 40 years [6],[8]  
Debt instrument, face amount               350,000,000                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
Piedmont’s % Ownership of Entity                 49.50% 49.50% 49.50% 49.50%                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
Useful life                         5 years 25 years 20 years 25 years 40 years                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
Real Estate:                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
Balance at the beginning of the year 4,699,311,000 4,666,188,000 4,681,313,000                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
Additions to/improvements of real estate 108,131,000 440,141,000 105,282,000                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
Assets disposed (77,768,000) (361,397,000) (72,586,000)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
Assets impaired 0 0 (8,489,000) [9]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
Write-offs of intangible assets (73,632,000) [10] (35,916,000) [10] 0 [10]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
Write-offs of fully depreciated/amortized assets (7,138,000) (9,705,000) (39,332,000)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
Balance at the end of the year 4,648,904,000 4,699,311,000 4,666,188,000                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
Accumulated Depreciation and Amortization:                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
Balance at the beginning of the year 935,716,000 918,578,000 840,545,000                             951,897,000 25,871,000 3,906,000     6,029,000     7,242,000     3,612,000     5,082,000       9,327,000 8,378,000 [1]     949,000 [1]     942,570,000 8,826,000     6,291,000 [2]     4,902,000 [2]     6,766,000     14,686,000     19,404,000     13,020,000 [3]     3,404,000     10,157,000     16,575,000     6,732,000     4,695,000     4,189,000     2,177,000 [2]     9,799,000     6,906,000     12,465,000     12,756,000     9,395,000     9,544,000 [3]     6,334,000     26,514,000 [3]     6,313,000     6,797,000     55,720,000 [3]     28,479,000 [3]     17,776,000 [3]     39,209,000     2,972,000     3,155,000     25,154,000     46,382,000     143,225,000     3,763,000     4,901,000     1,490,000     4,186,000     4,194,000     11,536,000     14,672,000 [3]     5,494,000     3,003,000 [3]     8,408,000     8,681,000     11,467,000     21,922,000     11,262,000 [4]     13,985,000 [5]     44,068,000     33,533,000     13,114,000     23,204,000     4,561,000     4,694,000     12,864,000     2,987,000     15,093,000 [3]     6,527,000     4,591,000     16,258,000     4,640,000     8,407,000     8,670,000     405,000     1,550,000     1,824,000     8,565,000     1,067,000     777,000     2,038,000     2,421,000     1,029,000     0 [6]      
Depreciation and amortization expense 139,196,000 147,440,000 131,000,000                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
Assets disposed (16,374,000) (84,681,000) (13,519,000)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
Write-offs of intangible assets (73,632,000) [10] (35,916,000) [10] 0 [10]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
Write-offs of fully depreciated/amortized assets (7,138,000) (9,705,000) (39,448,000)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
Balance at the end of the year 977,768,000 935,716,000 918,578,000                             951,897,000 25,871,000 3,906,000     6,029,000     7,242,000     3,612,000     5,082,000       9,327,000 8,378,000 [1]     949,000 [1]     942,570,000 8,826,000     6,291,000 [2]     4,902,000 [2]     6,766,000     14,686,000     19,404,000     13,020,000 [3]     3,404,000     10,157,000     16,575,000     6,732,000     4,695,000     4,189,000     2,177,000 [2]     9,799,000     6,906,000     12,465,000     12,756,000     9,395,000     9,544,000 [3]     6,334,000     26,514,000 [3]     6,313,000     6,797,000     55,720,000 [3]     28,479,000 [3]     17,776,000 [3]     39,209,000     2,972,000     3,155,000     25,154,000     46,382,000     143,225,000     3,763,000     4,901,000     1,490,000     4,186,000     4,194,000     11,536,000     14,672,000 [3]     5,494,000     3,003,000 [3]     8,408,000     8,681,000     11,467,000     21,922,000     11,262,000 [4]     13,985,000 [5]     44,068,000     33,533,000     13,114,000     23,204,000     4,561,000     4,694,000     12,864,000     2,987,000     15,093,000 [3]     6,527,000     4,591,000     16,258,000     4,640,000     8,407,000     8,670,000     405,000     1,550,000     1,824,000     8,565,000     1,067,000     777,000     2,038,000     2,421,000     1,029,000     0 [6]      
Impairment charge                                                                     7,000,000                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
Impairment loss on real estate assets $ 0 $ 0 $ 7,041,000     $ 53,000 $ 1,400,000                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
[1] Properties sold subsequent to December 31, 2012.
[2] Property is owned subject to a long-term ground lease.
[3] These properties collateralize the $350 Million Secured Pooled Facility.
[4] Piedmont purchased all of the membership interest in 1225 Equity, LLC, which own a 49.5% membership interest in 1225 Eye Street, N.W. Associates, which owns the 1225 Eye Street building. As a result of its ownership of 1225 Equity, LLC, Piedmont owns an approximate 49.5% in the 1225 Eye Street building. As the controlling member, Piedmont is deemed to have control of the entities and, as such, consolidates the joint ventures.
[5] Piedmont purchased all of the membership interest in 1201 Equity, LLC, which own a 49.5% membership interest in 1201 Eye Street, N.W. Associates, which owns the 1201 Eye Street building. As a result of its ownership of 1201 Equity, LLC, Piedmont owns an approximate 49.5% in the 1201 Eye Street building. As the controlling member, Piedmont is deemed to have control of the entities and, as such, consolidates the joint ventures.
[6] Represents solar panels at the 400 Bridgewater Crossing building, which are not included in Piedmont’s total building count.
[7] Undeveloped Land Parcels are not included in Piedmont’s total building count.
[8] Piedmont’s assets are depreciated or amortized using the straight-lined method over the useful lives of the assets by class. Generally, Tenant Improvements are amortized over the shorter of economic life or lease term, and Lease Intangibles are amortized over the lease term. Generally, Building Improvements are depreciated over 5 - 25 years, Land Improvements are depreciated over 20 - 25 years, and Buildings are depreciated over 40 years.
[9] Piedmont recorded an impairment charge against real estate assets of approximately $7.0 million related to the 111 Sylvan Avenue building at the time it was classified as held-for-sale in May 2010. This wholly-owned asset was subsequently sold in December 2010. In addition, the Fund IX, Fund XI, and REIT Joint Venture recorded an impairment loss on real estate assets of approximately $1.4 million during 2010 related to the 360 Interlocken building; however, Piedmont recorded its proporationate share of the charge (approximately $53,000) in the accompanying consolidated statements of income with other such net property operations as equity in income of unconsolidated joint ventures.
[10] Consists of write-offs of intangible lease assets related to lease restructurings, amendments and terminations.