Consolidated Statements of Stockholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Series C Preferred Stock	Series D Preferred Stock	Series E Preferred Stock	Total Stockholders’ Equity	Total Stockholders’ Equity Series C Preferred Stock	Total Stockholders’ Equity Series D Preferred Stock	Total Stockholders’ Equity Series E Preferred Stock	Preferred Stock Series C Preferred Stock	Preferred Stock Series D Preferred Stock	Preferred Stock Series E Preferred Stock	Common Stock	Capital in Excess of Par Value	Capital in Excess of Par Value Series C Preferred Stock	Capital in Excess of Par Value Series D Preferred Stock	Capital in Excess of Par Value Series E Preferred Stock	Retained Earnings (Loss)	Retained Earnings (Loss) Series C Preferred Stock	Retained Earnings (Loss) Series D Preferred Stock	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interests
Balances at at Dec. 31, 2011	$ 2,003,876				$ 2,002,498				$ 92,000	$ 0	$ 0	$ 1,049	$ 1,958,225				$ (44,946)			$ (3,830)	$ 1,378
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	141,937				142,015												142,015				(78)
Dividends declared and paid:
Preferred stock dividends declared and paid		(1,979)	(15,449)			(1,979)	(15,449)											(1,979)	(15,449)
Common stock dividends declared and paid	(155,733)				(155,733)							4	11,758				(167,495)
Redemption of 3,680,000 shares of Series C Preferred Stock	(3,098)	(92,000)				(92,000)			(92,000)					3,098				(3,098)
Issuance of stock	833		277,645		833		277,645			287,500			833		(9,855)
Issuance of common stock - stock purchase program	44,412				44,412							17	44,395
Issuance of common stock - ATM equity program	129,092				129,092							43	129,049
Issuance of shares of restricted common stock	335				335							4	331
Equity component of convertible debt	(41,486)				(41,486)								(41,486)
Stock issuance costs	(2,265)				(2,265)								(2,265)
Performance incentive plan
Performance incentive plan	(451)				(451)								(451)
Amortization of deferred compensation	7,370				7,370								7,370
Amortization of interest rate hedges	231				231															231
Fair value forward starting swaps	0
Unrealized gain – commercial mortgage residual interests	1,132				1,132															1,132
Valuation adjustments – available-for-sale securities	85				85															85
Balances at at Dec. 31, 2012	2,297,585				2,296,285				0	287,500	0	1,117	2,101,002				(90,952)			(2,382)	1,300
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	160,085				160,145												160,145				(60)
Dividends declared and paid:
Preferred stock dividends declared and paid	(8,876)		(19,047)		(8,876)		(19,047)										(8,876)		(19,047)
Common stock dividends declared and paid	(174,162)				(174,162)							4	14,941				(189,107)
Redemption of 3,680,000 shares of Series C Preferred Stock	0
Issuance of stock	744			277,644	744			277,644			287,500		744			(9,856)
Issuance of common stock - stock purchase program	10,461				10,461							3	10,458
Issuance of common stock - ATM equity program	242,418				242,418							70	242,348
Issuance of common stock - conversion of 2028 Notes	85,224				85,224							24	85,200
Issuance of shares of restricted common stock	(210)				(210)							3	(213)
Equity component of convertible debt	(93,450)				(93,450)								(93,450)
Stock issuance costs	(3,774)				(3,774)								(3,774)
Performance incentive plan
Amortization of deferred compensation	6,715				6,715								6,715
Amortization of interest rate hedges	438				438															438
Fair value forward starting swaps	(3,141)				(3,141)															(3,141)
Unrealized gain – commercial mortgage residual interests	(438)				(438)															(438)
Valuation adjustments – available-for-sale securities	69				69															69
Distributions to noncontrolling interests													(949)							949
Balances at at Dec. 31, 2013	2,778,285				2,777,045				0	287,500	287,500	1,221	2,353,166				(147,837)			(4,505)	1,240
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	191,170				190,601												190,601				569
Dividends declared and paid:
Preferred stock dividends declared and paid	(16,387)		(19,047)		(16,387)		(19,047)										(16,387)		(19,047)
Common stock dividends declared and paid	(192,711)				(192,711)							3	11,443				(204,157)
Redemption of 3,680,000 shares of Series C Preferred Stock	0
Issuance of stock	209,240				209,240							55	209,185
Issuance of common stock - stock purchase program	3,371				3,371							1	3,370
Issuance of common stock - ATM equity program	137,115				137,115							38	137,077
Issuance of shares of restricted common stock	(309)				(309)							4	(313)
Stock issuance costs	(10,683)				(10,683)								(10,683)
Performance incentive plan
Amortization of deferred compensation	8,433				8,433								8,433
Amortization of interest rate hedges	1,129				1,129															1,129
Fair value forward starting swaps	(6,312)				(6,312)															(6,312)
Unrealized gain – commercial mortgage residual interests	875				875															875
Realized gain – commercial mortgage residual interests	163				163															163
Valuation adjustments – available-for-sale securities	111				111															111
Realized gain – available-for-sale securities	(119)				(119)															(119)
Distributions to noncontrolling interests	(1,232)																				(1,232)
Balances at at Dec. 31, 2014	$ 3,083,092				$ 3,082,515				$ 0	$ 287,500	$ 287,500	$ 1,322	$ 2,711,678				$ (196,827)			$ (8,658)	$ 577