(Common Units) (Narrative) (Details) (USD $)	0 Months Ended				12 Months Ended
	Oct. 31, 2012	Jul. 31, 2012	Apr. 30, 2012	Jan. 27, 2012	Dec. 31, 2012 Y	Nov. 08, 2012
OP Units [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Distributions Declared To OP And LTIP Units Per Unit						$ 0.65
Distributions Declared To Outperformance Awards Long Term Incentive Plan Units Per Unit						$ 0.065
OP Units for redemption (in shares)					1,110,660
Redemption of OP units issued on conversion of Series Two Preferred Units (in shares)					153,605
Redemption of OP units issued on conversion of LTIP Units (in shares)					544,729
Outperformance Awards LTIP Units distribution as percentage of OP Unit distribution prior to measurement date					10.00%
Distributions made to OP and LTIP units per unit (in dollars per share)	$ 0.55	$ 0.55	$ 0.55	$ 0.55
Distribution paid to outperformance awards, OPP Units (in dollars per share)	$ 0.055	$ 0.055	$ 0.055	$ 0.055
Restriction on redemption of OP Unit to Common Stock (in years)					1
Redemption of OP Unit equivalence to Common Stock (in shares)					1
Common units of operating partnership if converted value					$ 1,800,000,000
Value of Series Two Preferred Units assuming conversion					$ 138,300,000
OPP Units 2011 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Outperformance awards in LTIP Units (in shares)					400,000
OPP Units 2012 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Outperformance awards in LTIP Units (in shares)					400,000
OP Units [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Closing price of common stock (in dollars per share)					$ 105.81
Quarter 4 2011 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Dividend payable date					Jan. 27, 2012
Quarter 4 2011 [Member] | OP Units [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Dividend payable date					Jan. 27, 2012
Holders of record date					Dec. 31, 2011
Quarter 1 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Dividend payable date					Apr. 30, 2012
Quarter 1 [Member] | OP Units [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Dividend payable date					Apr. 30, 2012
Holders of record date					Mar. 30, 2012
Quarter 2 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Dividend payable date					Jul. 31, 2012
Quarter 2 [Member] | OP Units [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Dividend payable date					Jul. 31, 2012
Holders of record date					Jun. 29, 2012
Quarter 3 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Dividend payable date					Oct. 31, 2012
Quarter 3 [Member] | OP Units [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Dividend payable date					Oct. 31, 2012
Holders of record date					Sep. 28, 2012
Quarter 4 2012 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Dividend payable date					Jan. 29, 2013
Dividends Payable, Date Declared					Nov. 08, 2012
Quarter 4 2012 [Member] | OP Units [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Dividend payable date					Jan. 29, 2013
Holders of record date					Dec. 31, 2012
Dividends Payable, Date Declared					Nov. 08, 2012