Consolidated Statements of Stockholders' Equity (USD $) In Thousands, except Share data	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Cumulative Distributions in Excess of Earnings [Member]	Redeemable Common Stock [Member]	Other Comprehensive Loss [Member]	Non-controlling Interest [Member]
Balance, value at Dec. 31, 2009	$ 2,606,882	$ 1,589	$ 3,477,168	$ (798,561)	$ (75,164)	$ (3,866)	$ 5,716
Balance, shares at Dec. 31, 2009		158,917,000
Net proceeds from issuance of common stock, shares		13,800,000
Net proceeds from issuance of common stock, value	184,404	138	184,266
Redemption of fractional shares of common stock, shares		(200,000)
Redemption of fractional shares of common stock, value	(2,902)	(2)	(2,900)
Change in redeemable common stock outstanding	75,164				75,164
Dividends to common stockholders ($1.26 (YTD 2010) and $0.945 (YTD 2011) per share), distributions to noncontrolling interest, and dividends reinvested	(216,988)		(33)	(216,940)			(15)
Shares issued under the 2007 Omnibus Incentive Plan, net of tax, shares		141,000
Shares issued under the 2007 Omnibus Incentive Plan, net of tax, value	2,809	2	2,807
Net income attributable to noncontrolling interest	531						531
Components of comprehensive income:
Net income	120,379			120,379
Net change in interest rate swap/derivatives	3,175					3,175
Comprehensive income	123,554
Balance, value at Dec. 31, 2010	2,773,454	1,727	3,661,308	(895,122)		(691)	6,232
Balance, shares at Dec. 31, 2010	172,658,489	172,658,000
Offering costs associated with issuance of common stock	(479)		(479)
Dividends to common stockholders ($1.26 (YTD 2010) and $0.945 (YTD 2011) per share), distributions to noncontrolling interest, and dividends reinvested	(165,636)		(168)	(163,268)			(2,200)
Shares issued under the 2007 Omnibus Incentive Plan, net of tax, shares	168,502	169,000
Shares issued under the 2007 Omnibus Incentive Plan, net of tax, value	2,495	1	2,494
Net income attributable to noncontrolling interest	378						378
Components of comprehensive income:
Net income	106,020			106,020
Net change in interest rate swap/derivatives	691					691
Comprehensive income	106,711
Balance, value at Sep. 30, 2011	$ 2,716,923	$ 1,728	$ 3,663,155	$ (952,370)		$ 0	$ 4,410
Balance, shares at Sep. 30, 2011	172,826,991	172,827,000