Consolidated Statement of Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Preferred stock	Common stock	Additional Paid in Capital	Accumulated Other Comprehensive Income (loss)	Retained earnings, distributions in excess of earnings	Total Shareholders' Equity	Non-Controlling Interest
Beginning Balance at Dec. 31, 2010	$ 1,050,814		$ 499	$ 1,002,809	$ 24,015	$ (8,173)	$ 1,019,150	$ 31,664
Beginning Balance (in shares) at Dec. 31, 2010			49,854,196
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	286,797					281,915	281,915	4,882
Other comprehensive income (loss)	(423,906)				(417,306)		(417,306)	(6,600)
Proceeds from issuance of common stock, net of offering costs (in shares)			65,533,550
Proceeds from issuance of common stock, net of offering costs	1,297,200		655	1,296,545			1,297,200
Stocks awards			7,949
Common stock dividends	(288,810)					(288,810)	(288,810)
Common unit dividends	(4,874)							(4,874)
Amortization of equity-based compensation (shares)
Amortization of equity-based compensation	192			189			189	3
Ending Balance at Dec. 31, 2011	1,917,413		1,154	2,299,543	(393,291)	(15,068)	1,892,338	25,075
Ending Balance (in shares) at Dec. 31, 2011			115,395,695
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	344,008					339,885	339,885	4,123
Other comprehensive income (loss)	485,653				479,727		479,727	5,926
Proceeds from issuance of common stock, net of offering costs (in shares)			787,882
Proceeds from issuance of common stock, net of offering costs	16,423		8	16,415			16,423
Proceeds from issuance of preferred stock, net of offering costs (in shares)		5,600,000
(Cost) proceeds from issuance of preferred stock, net of offering costs	135,362	135,362					135,362
Stocks awards			11,923
Common stock dividends	(300,574)					(300,574)	(300,574)
Common unit dividends	(3,706)							(3,706)
Preferred stock dividends	(5,395)					(5,395)	(5,395)
Amortization of equity-based compensation (shares)
Amortization of equity-based compensation	336			332			332	4
Ending Balance at Dec. 31, 2012	2,589,520	135,362	1,162	2,316,290	86,436	18,848	2,558,098	31,422
Ending Balance (in shares) at Dec. 31, 2012		5,600,000	116,195,500
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	143,106					141,620	141,620	1,486
Other comprehensive income (loss)	(245,945)				(243,429)		(243,429)	(2,516)
Proceeds from issuance of common stock, net of offering costs (in shares)			19,020,106
Proceeds from issuance of common stock, net of offering costs	396,470		190	396,280			396,470
(Cost) proceeds from issuance of preferred stock, net of offering costs	(6)	(6)					(6)
Repurchase of shares of common stock (in shares)			(10,720,003)
Repurchase of shares of common stock	(160,526)		(107)	(160,419)			(160,526)
Stocks awards			14,643
Common stock dividends	(305,574)					(305,574)	(305,574)
Common unit dividends	(3,276)							(3,276)
Preferred stock dividends	(10,851)					(10,851)	(10,851)
Amortization of equity-based compensation (shares)
Amortization of equity-based compensation	317			313			313	4
Ending Balance at Dec. 31, 2013	$ 2,403,235	$ 135,356	$ 1,245	$ 2,552,464	$ (156,993)	$ (155,957)	$ 2,376,115	$ 27,120
Ending Balance (in shares) at Dec. 31, 2013		5,600,000	124,510,246