Consolidated Statements of Stockholders' Equity (USD $)	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	Common Stock Series C Preferred Stock	Common Stock Series D Preferred Stock	Common Stock Series E Preferred 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	Retained Earnings Series C Preferred Stock	Retained Earnings Series D Preferred Stock	Retained Earnings Series E Preferred Stock	Accumulated Other Comprehensive Income	Accumulated Other Comprehensive Income Series C Preferred Stock	Accumulated Other Comprehensive Income Series D Preferred Stock	Accumulated Other Comprehensive Income Series E Preferred Stock	Noncontrolling Interests	Noncontrolling Interests Series C Preferred Stock	Noncontrolling Interests Series D Preferred Stock	Noncontrolling Interests Series E Preferred Stock
Balances at Dec. 31, 2010	$ 1,528,774,000				$ 1,527,483,000				$ 92,000,000			$ 838,000				$ 1,429,750,000				$ 3,234,000				$ 1,661,000				$ 1,291,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	92,416,000				92,325,000															92,325,000								91,000
Dividends declared and paid:
Preferred stock dividends declared and paid		(6,785,000)				(6,785,000)															(6,785,000)
Common stock dividends declared and paid	(120,063,000)				(120,063,000)							5,000				13,652,000				(133,720,000)
Redemption of 3,680,000 shares of Series C Preferred Stock	0
Issuance of stock	447,863,000				447,863,000							173,000				447,690,000
Issuance of common stock - stock purchase program	79,794,000				79,794,000							32,000				79,762,000
Issuance of shares of restricted common stock	(56,000)				(56,000)							1,000				(57,000)
Stock issuance costs	(19,453,000)				(19,453,000)											(19,453,000)
Performance incentive plan
Performance incentive plan	(513,000)				(513,000)											(513,000)
Amortization of deferred compensation	7,394,000				7,394,000											7,394,000
Amortization of interest rate hedges	9,000				9,000																			9,000
Fair value treasury locks	(5,218,000)				(5,218,000)																			(5,218,000)
Unrealized loss – commercial mortgage residual interests	(246,000)				(246,000)																			(246,000)
Stock value adjustments	(36,000)				(36,000)																			(36,000)
Contributions from noncontrolling interests	41,000																											41,000
Distributions to noncontrolling interests	(45,000)																											(45,000)
Balances at Dec. 31, 2011	2,003,876,000				2,002,498,000				92,000,000			1,049,000				1,958,225,000				(44,946,000)				(3,830,000)				1,378,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	141,937,000				142,015,000															142,015,000								(78,000)
Dividends declared and paid:
Preferred stock dividends declared and paid		(1,979,000)	(15,449,000)			(1,979,000)	(15,449,000)														(1,979,000)	(15,449,000)
Common stock dividends declared and paid	(155,733,000)				(155,733,000)							4,000				11,758,000				(167,495,000)
Redemption of 3,680,000 shares of Series C Preferred Stock	(3,098,000)	(92,000,000)				(92,000,000)			(92,000,000)								3,098,000				(3,098,000)
Issuance of stock	833,000		277,645,000		833,000		277,645,000			287,500,000						833,000		(9,855,000)
Issuance of common stock - stock purchase program	44,412,000				44,412,000							17,000				44,395,000
Issuance of common stock - ATM equity program	129,092,000				129,092,000							43,000				129,049,000
Issuance of shares of restricted common stock	335,000				335,000							4,000				331,000
Equity component of convertible debt	(41,486,000)				(41,486,000)											(41,486,000)
Stock issuance costs	(2,265,000)				(2,265,000)											(2,265,000)
Performance incentive plan
Performance incentive plan	(451,000)				(451,000)											(451,000)
Amortization of deferred compensation	7,370,000				7,370,000											7,370,000
Amortization of interest rate hedges	231,000				231,000																			231,000
Fair value treasury locks	0
Unrealized loss – commercial mortgage residual interests	1,132,000				1,132,000																			1,132,000
Stock value adjustments	85,000				85,000																			85,000
Balances at Dec. 31, 2012	2,297,585,000				2,296,285,000					287,500,000		1,117,000				2,101,002,000				(90,952,000)				(2,382,000)				1,300,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	160,085,000				160,145,000															160,145,000								(60,000)
Dividends declared and paid:
Preferred stock dividends declared and paid	(8,876,000)		(19,047,000)		(8,876,000)		(19,047,000)													(8,876,000)		(19,047,000)
Common stock dividends declared and paid	(174,162,000)				(174,162,000)							4,000				14,941,000				(189,107,000)
Redemption of 3,680,000 shares of Series C Preferred Stock	0
Issuance of stock	744,000			277,644,000	744,000			277,644,000			287,500,000					744,000			(9,856,000)
Issuance of common stock - stock purchase program	10,461,000				10,461,000							3,000				10,458,000
Issuance of common stock - ATM equity program	242,418,000				242,418,000							70,000				242,348,000
Issuance of common stock - conversion of 2028 Notes	85,224,000				85,224,000							24,000				85,200,000
Issuance of shares of restricted common stock	(210,000)				(210,000)							3,000				(213,000)
Equity component of convertible debt	(93,450,000)				(93,450,000)											(93,450,000)
Stock issuance costs	(3,774,000)				(3,774,000)											(3,774,000)
Performance incentive plan
Amortization of deferred compensation	6,715,000				6,715,000											6,715,000
Amortization of interest rate hedges	438,000				438,000																			438,000
Fair value treasury locks	(3,141,000)				(3,141,000)																			(3,141,000)
Unrealized loss – commercial mortgage residual interests	(438,000)				(438,000)																			(438,000)
Stock value adjustments	69,000				69,000																			69,000
Noncontrolling interests																(949,000)								949,000
Balances at Dec. 31, 2013	$ 2,778,285,000				$ 2,777,045,000					$ 287,500,000	$ 287,500,000	$ 1,221,000				$ 2,353,166,000				$ (147,837,000)				$ (4,505,000)				$ 1,240,000