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 D Preferred Stock	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
Beginning balance 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		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 of 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)
Ending balance 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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	265,371				264,973											264,973					398
Dividends declared and paid:
Preferred stock dividends declared and paid		(3,598)	(16,387)	(17,940)		(3,598)	(16,387)	(17,940)									(3,598)	(16,387)	(17,940)
Common stock dividends declared and paid	(268,293)				(268,293)							2	8,825			(277,120)
Redemption of 11,500,000 depositary shares of Series D preferred stock		$ (287,500)				$ (287,500)			(287,500)					$ 9,855			$ (9,855)
Issuance of common stock:
Issuance of stock	1,176				1,176							1	1,175
Issuance of common stock - stock purchase plan	563				563								563
Issuance of common stock - ATM equity program	247,604				247,604							58	247,546
Issuance of shares of restricted common stock	(231)				(231)							3	(234)
Stock issuance costs	(3,782)				(3,782)								(3,782)
Amortization of deferred compensation	12,630				12,630								12,630
Amortization of interest rate hedges	1,932				1,932															1,932
Fair value of forward starting swaps	(7,688)				(7,688)															(7,688)
Valuation adjustments – available-for-sale securities	209				209															209
Distributions to noncontrolling interests	(84)																				(84)
Noncontrolling interests	0				126								126								(126)
Ending balance at Dec. 31, 2017	3,840,910				3,840,593				0	287,500	345,000	1,537	3,599,475			(379,181)				(13,738)	317
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	292,485				292,447											292,447					38
Dividends declared and paid:
Preferred stock dividends declared and paid			$ (16,387)	$ (17,940)			$ (16,387)	$ (17,940)										$ (16,387)	$ (17,940)
Common stock dividends declared and paid	(290,201)				(290,201)							3	12,960			(303,164)
Issuance of common stock:
Issuance of stock	1,375				1,375								1,375
Issuance of common stock - stock purchase plan	426				426								426
Issuance of common stock - ATM equity program	332,018				332,018							74	331,944
Issuance of shares of restricted common stock	(89)				(89)							2	(91)
Stock issuance costs	(3,947)				(3,947)								(3,947)
Amortization of deferred compensation	7,913				7,913								7,913
Amortization of interest rate hedges	3,664				3,664															3,664
Fair value of forward starting swaps	4,080				4,080															4,080
Valuation adjustments – available-for-sale securities	298				298															298
Ending balance at Dec. 31, 2018	$ 4,154,605				$ 4,154,250				$ 0	$ 287,500	$ 345,000	$ 1,616	$ 3,950,055			$ (424,225)				$ (5,696)	$ 355