Partners' Capital (Details) (USD $)	0 Months Ended				9 Months Ended					9 Months Ended					0 Months Ended	60 Months Ended					9 Months Ended					9 Months Ended
	Jul. 31, 2013	Apr. 30, 2013	Mar. 27, 2013	Jan. 29, 2013	Sep. 30, 2013	Sep. 30, 2012	Sep. 18, 2013	Dec. 31, 2012	Sep. 30, 2013 ATM Program [Member]	Sep. 30, 2013 Issued in conjunction with debt exchange for 3.75% exchangeable senior notes [Member]	Sep. 30, 2013 Quarter 4 2012 [Member]	Sep. 30, 2013 Quarter 1 2013 [Member]	Sep. 30, 2013 Quarter 2 2013 [Member]	Sep. 30, 2013 Quarter 3 2013 [Member]	May 15, 2013 Series B Cumulative Redeemable Preferred Stock [Member]	Mar. 26, 2018 Series B Cumulative Redeemable Preferred Stock [Member]	Mar. 27, 2018 Series B Cumulative Redeemable Preferred Stock [Member]	Sep. 30, 2013 Series B Cumulative Redeemable Preferred Stock [Member]	Sep. 18, 2013 Series B Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2012 Series B Cumulative Redeemable Preferred Stock [Member]	Sep. 30, 2013 Series B Cumulative Redeemable Preferred Stock [Member] Quarter 2 2013 [Member]	Sep. 30, 2013 Series B Cumulative Redeemable Preferred Stock [Member] Quarter 3 2013 [Member]	Sep. 30, 2013 Series B Cumulative Redeemable Preferred Stock [Member] Quarter 4 2013 [Member]	Mar. 27, 2018 Depository shares of Series B Cumulative Redeemable Preferred [Member]	Sep. 30, 2013 Depository shares of Series B Cumulative Redeemable Preferred [Member]	Sep. 30, 2013 OP Units [Member] Issued in conjunction with debt exchange for 3.75% exchangeable senior notes [Member]
Class of Stock [Line Items]
General partnership units (in units)					1,695,893			1,689,580
Limited partnership units (in units)					150,694,702			149,911,629
At the market stock offering program, aggregate value of common stock									$ 600,000,000
At the market stock offering program remaining amount available for issuance									305,300,000
Shares of its Common Stock in connection with the redemption of an equal number of OP Units (in shares)					336,935
Dividend payable date											Jan. 29, 2013	Apr. 30, 2013	Jul. 31, 2013	Oct. 31, 2013							May 15, 2013	Aug. 15, 2013	Nov. 15, 2013
Dividend paid on common stock (in dollars per share)	$ 0.65	$ 0.65		$ 0.65											$ 32.8125
Dividend shareholder of record date											Dec. 31, 2012	Mar. 29, 2013	Jun. 28, 2013	Sep. 30, 2013									Nov. 05, 2013
Dividends payable, date declared														Sep. 18, 2013									Sep. 18, 2013
Dividends payable (in dollars per share)							$ 0.65												$ 32.8125
Series B, Units Outstanding																		80,000		0					8,000,000
Series B, Liquidation Preference Per Unit																	$ 2,500.00	$ 2,500.00		$ 0				$ 25.00	$ 25.00
Proceeds from Issuance of Series B Preferred Stock			$ 193,600,000		$ 193,623,000	$ 0
Ratio of depository shares to shares of Series B Preferred Stock																		0.01
Series B, Dividend Rate, Percentage																5.25%
Shares issued in conjunction with exchange of 3.75% exchangeable senior notes										419,116																419,116
Coupon/Stated Rate (percent)										3.75%