CONSOLIDATED STATEMENTS OF EQUITY - USD ($) $ in Thousands	Total	Series D Preferred Stock	Series E Preferred Stock	Series F Preferred Stock	Total Stockholders’ Equity	Total Stockholders’ Equity Series D Preferred Stock	Total Stockholders’ Equity Series E Preferred Stock	Total Stockholders’ Equity Series F Preferred Stock	Preferred Stock Series D Preferred Stock	Preferred Stock Series E Preferred Stock	Preferred Stock Series F Preferred Stock	Common Stock	Capital in Excess of Par Value	Capital in Excess of Par Value Series F Preferred Stock	Retained Earnings (Loss)	Retained Earnings (Loss) Series D Preferred Stock	Retained Earnings (Loss) Series E Preferred Stock	Retained Earnings (Loss) Series F Preferred Stock	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interests
Balances at at Dec. 31, 2013	$ 2,778,285				$ 2,777,045				$ 287,500	$ 287,500	$ 0	$ 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		$ (19,047)	$ (16,387)			$ (19,047)	$ (16,387)									$ (19,047)	$ (16,387)
Common stock dividends declared and paid	(192,711)				(192,711)							3	11,443		(204,157)				0	0
Issuance of common stock:
Issuance of stock	209,240											55	209,185
Issuance of common stock - stock purchase plan	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)
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 loss – 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				287,500	287,500	0	1,322	2,711,678		(196,827)				(8,658)	577
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	197,961				197,836										197,836					125
Dividends declared and paid:
Preferred stock dividends declared and paid		(19,047)	(16,387)			(19,047)	(16,387)									(19,047)	(16,387)
Common stock dividends declared and paid	(221,811)				(221,811)							2	6,886		(228,699)
Issuance of common stock:
Issuance of stock	991				991								991
Issuance of common stock - stock purchase plan	455				455								455
Issuance of common stock - ATM equity program	325,084				325,084							86	324,998
Issuance of shares of restricted common stock	(309)				(309)							2	(311)
Stock issuance costs	(4,178)				(4,178)								(4,178)
Amortization of deferred compensation	8,679				8,679								8,679
Amortization of interest rate hedges	1,902				1,902														1,902
Fair value forward starting swaps	(13,369)				(13,369)														(13,369)
Unrealized loss – commercial mortgage residual interests	(585)				(585)														(585)
Realized gain – commercial mortgage residual interests	246				246														246
Valuation adjustments – available-for-sale securities	112				112														112
Contributions from noncontrolling interests	334																			334
Distributions to noncontrolling interests	(362)																			(362)
Sale of noncontrolling interests	(415)																			(415)
Balances at at Dec. 31, 2015	3,342,393				3,342,134				287,500	287,500	0	1,412	3,049,198		(263,124)				(20,352)	259
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	239,506				239,500										239,500					6
Dividends declared and paid:
Preferred stock dividends declared and paid		$ (19,047)	$ (16,387)	$ (3,189)		$ (19,047)	$ (16,387)	$ (3,189)								$ (19,047)	$ (16,387)	$ (3,189)
Common stock dividends declared and paid	(249,056)				(249,056)							2	7,949		(257,007)
Issuance of common stock:
Issuance of stock	1,148			$ 334,103	1,148						345,000	0	1,148	$ (10,897)
Issuance of common stock - stock purchase plan	389				389								389
Issuance of common stock - ATM equity program	269,962				269,962							57	269,905
Issuance of shares of restricted common stock	(262)				(262)							2	(264)
Stock issuance costs	(4,266)				(4,266)								(4,266)
Amortization of deferred compensation	9,609				9,609								9,609
Amortization of interest rate hedges	2,802				2,802														2,802
Fair value forward starting swaps	13,345				13,345														13,345
Unrealized loss – commercial mortgage residual interests	(182)				(182)														(182)
Realized gain – commercial mortgage residual interests	(4,272)				(4,272)														(4,272)
Valuation adjustments – available-for-sale securities	468				468														468
Distributions to noncontrolling interests	(136)																			(136)
Balances at at Dec. 31, 2016	$ 3,916,928				$ 3,916,799				$ 287,500	$ 287,500	$ 345,000	$ 1,473	$ 3,322,771		$ (319,254)				$ (8,191)	$ 129