Subsequent Events subsequent Events (Details) (USD $)	12 Months Ended				0 Months Ended																0 Months Ended		0 Months Ended		3 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Feb. 01, 2013	Jan. 28, 2013 MYLTIP [Member] Y	Jan. 28, 2013 MYLTIP Vesting 2016 [Member] MYLTIP [Member]	Jan. 28, 2013 MYLTIP Vesting 2017 [Member] MYLTIP [Member]	Jan. 28, 2013 MYLTIP Vesting 2018 [Member] MYLTIP [Member]	Jan. 28, 2013 Cohen & Steers Realty Majors Portfolio Index [Member] MYLTIP [Member]	Jan. 28, 2013 NAREIT Office Index adjusted [Member] MYLTIP [Member]	Jan. 28, 2013 Minimum [Member] MYLTIP [Member]	Jan. 28, 2013 Maximum [Member] MYLTIP [Member]	Jan. 28, 2013 Threshold [Member] MYLTIP [Member]	Jan. 28, 2013 Target [Member] MYLTIP [Member]	Jan. 28, 2013 High [Member] MYLTIP [Member]	Jan. 28, 2013 Exceptional [Member] MYLTIP [Member]	Feb. 01, 2013 Restricted Stock [Member]	Dec. 31, 2012 Restricted Stock [Member]	Dec. 31, 2011 Restricted Stock [Member]	Dec. 31, 2010 Restricted Stock [Member]	Feb. 05, 2013 Kingstowne One [Member]	Jan. 29, 2013 Reston Land Parcel [Member]	Feb. 06, 2013 535 Mission [Member] floor sqft	Feb. 26, 2013 Pursuit of Transbay Tower [Member]	Feb. 06, 2013 Pursuit of Transbay Tower [Member]
Subsequent Event [Line Items]
TRS Measurement, Years					3
Weighted Percentage of Index Used to Compare to TRS									50.00%	50.00%
Potential Awards Earned											$ 0	$ 30,700,000
Indices Used to Compare TRS					2
Number of Tiers					4
Amount of Each Tier													5,100,000	10,200,000	20,500,000	30,700,000
Percentage of annualized TRS for Reduction of Earned Awards					2.00%
Percentage to Cause Some Awards to be Earned Even if on a Relative Basis it Would Not Result in any Earned Awards					10.00%
Vesting Percentage						25.00%	25.00%	50.00%
Vesting Date						Feb. 04, 2016	Feb. 04, 2017	Feb. 04, 2018
Distributions Percent Before Measurement Date					10.00%
Value of MYLTIP Awards					8,100,000
MYLTIP Value Amortized Into Earnings, Years					5
Shares issued	151,680,109	148,186,511															35,087	20,756	19,030	69,499
LTIP units issued (in shares)				153,006
Non-qualified stock options issued (in shares)				201,373
Repayments of mortgage notes payable	253,877,000	1,251,841,000	730,191,000																		17,000,000
Coupon/Stated Rate																					5.96%
Maturity Date																					May 05, 2013
Penalty for early repayment of debt																					0.0
Acquisition aggregate purchase price																						$ 27,000,000	$ 71,000,000
Number of floors in building																							27
Net Rentable Area																							307,000
Partners Joint Venture Ownership Percentage																								5.00%	50.00%
Companys Joint Venture Ownership Percentage																								95.00%