Consolidated Statement of Changes in Equity - USD ($) $ in Thousands	Total	Parent Company [Member]	Partnership Interest [Member]	Other Comprehensive Income (Loss) [Member] Parent Company [Member]	Preferred Stock [Member] Parent Company [Member]	Common Stock [Member] Parent Company [Member]	Treasury Stock [Member] Parent Company [Member]	Additional Paid-in Capital [Member] Parent Company [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Other Comprehensive Income (Loss) [Member] Parent Company [Member]	Distributions in Excess of Net Income [Member] Parent Company [Member]	Total Stockholders' Equity [Member] Parent Company [Member]	Noncontrolling Interest Exchangeable Operating Partnership Units [Member] Parent Company [Member]	Noncontrolling Interests in Limited Partners' Interest in Consolidated Partnerships [Member] Parent Company [Member]	Noncontrolling Interest [Member] Parent Company [Member]	Preferred Stock [Member] Parent Company [Member]	Preferred Stock [Member] Preferred Stock [Member] Parent Company [Member]	Preferred Stock [Member] Common Stock [Member] Parent Company [Member]	Preferred Stock [Member] Treasury Stock [Member] Parent Company [Member]	Preferred Stock [Member] Additional Paid-in Capital [Member] Parent Company [Member]	Preferred Stock [Member] Accumulated Other Comprehensive Income (Loss) [Member] Parent Company [Member]	Preferred Stock [Member] Distributions in Excess of Net Income [Member] Parent Company [Member]	Preferred Stock [Member] Total Stockholders' Equity [Member] Parent Company [Member]	Preferred Stock [Member] Noncontrolling Interest Exchangeable Operating Partnership Units [Member] Parent Company [Member]	Preferred Stock [Member] Noncontrolling Interests in Limited Partners' Interest in Consolidated Partnerships [Member] Parent Company [Member]	Preferred Stock [Member] Noncontrolling Interest [Member] Parent Company [Member]	Common Stock [Member] Parent Company [Member]	Common Stock [Member] Preferred Stock [Member] Parent Company [Member]	Common Stock [Member] Common Stock [Member] Parent Company [Member]	Common Stock [Member] Treasury Stock [Member] Parent Company [Member]	Common Stock [Member] Additional Paid-in Capital [Member] Parent Company [Member]	Common Stock [Member] Accumulated Other Comprehensive Income (Loss) [Member] Parent Company [Member]	Common Stock [Member] Distributions in Excess of Net Income [Member] Parent Company [Member]	Common Stock [Member] Total Stockholders' Equity [Member] Parent Company [Member]	Common Stock [Member] Noncontrolling Interest Exchangeable Operating Partnership Units [Member] Parent Company [Member]	Common Stock [Member] Noncontrolling Interests in Limited Partners' Interest in Consolidated Partnerships [Member] Parent Company [Member]	Common Stock [Member] Noncontrolling Interest [Member] Parent Company [Member]	Partners Capital Total [Member]	Noncontrolling Interest [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Limited Partner [Member]	General Partner [Member]
Beginning balance at Dec. 31, 2016	$ 2,624,502	$ 2,624,502			$ 325,000	$ 1,045	$ (17,062)	$ 3,294,923		$ (18,346)	$ (994,259)	$ 2,591,301	$ (1,967)	$ 35,168	$ 33,201																							$ 2,589,334	$ 35,168	$ (18,346)	$ (1,967)	$ 2,609,647
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss) Attributable to Parent		(21,367)	$ (21,386)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	(20,715)	(20,715)	(20,715)		0	0	0	0		0		(21,367)	(19)	671	652																							(21,386)	671	0	(19)	(21,367)
Current period other comprehensive income, net	2,620	2,618	2,618	$ 2,620	0	0	0	0	$ 2,554	2,555	0	2,555	2	63																								2,557		2,555	2	0
Other comprehensive income attributable to noncontrolling interests		65	63												65																								63
Adjustments to Additional Paid in Capital, Share-based Compensation, Other Long-term Incentive Plans, Requisite Service Period Recognition		1			0	0	(411)	412		0	0	1	0	0	0
Restricted stock issued, net of amortization	3,733	3,733			0	2	0	3,731		0	0	3,733	0	0	0																							3,733	0	0	0	3,733
Common stock redeemed for taxes withheld for stock based compensation, net																											$ 18,220	$ 0	$ 1	$ 0	$ 18,219	$ 0	$ 0	$ 18,220	$ 0	$ 0	$ 0
Common stock issued under dividend reinvestment plan		301	301																								301	0	0	0	301	0	0	301	0	0	0
Common stock issued, net of issuance costs																											4,479,686	0	655	0	4,479,031	0	0	4,479,686	0	0	0
Contributions from partners	153	153			0	0	0	0		0	0	0	0	153	153																							0	153	0	0	0
Distributions to partners	(54,317)	(838)			0	0	0	0		0	0	0	0	(838)	(838)																							(53,479)	(838)	0	(79)	53,400
Cash dividends declared: preferred stock/unit	3,241	3,241			0	0	0	0		0	3,241	3,241	0	0	0																							3,241	0	0	0	3,241
Redemption of preferred stock	250,000															$ 250,000	$ 250,000	$ 0	$ 0	$ (8,615)	$ 0	$ 8,615	$ 250,000	$ 0	$ 0	$ 0												250,000	0	0	0	250,000
Preferred stock		(11,856)
Cash dividends declared - common stock/unit		53,479			0	0	0	0		0	53,400	53,400	79	0	79
Ending Balance at Mar. 31, 2017	6,764,502	6,764,503			75,000	1,701	(17,473)	7,768,794		(15,791)	(1,080,882)	6,731,349	(2,063)	35,217	33,154																							6,729,285	35,217	(15,791)	(2,063)	6,747,139
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	30,903	30,903			0	0	0	0	(14)	12	30,889	30,901	0	2	2																							30,901	2	12	0	30,889
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	6,763,957	6,763,957			0	1,714	(18,307)	7,873,104		(6,277)	(1,127,281)	6,722,953	10,907	30,097	41,004																							6,733,860	30,097	(6,277)	10,907	6,729,230
Beginning balance at Dec. 31, 2017	6,733,054	6,733,054			0	1,714	(18,307)	7,873,104		(6,289)	(1,158,170)	6,692,052	10,907	30,095	41,002																							6,702,959	30,095	(6,289)	10,907	6,698,341
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss) Attributable to Parent		52,660	52,771
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	53,465	53,465	53,465		0	0	0	0		0		52,660	111	694	805																							52,771	694	0	111	52,660
Current period other comprehensive income, net	11,524	11,524	11,524		0	0	0	0	$ 11,041	11,041	0	11,041	23	460																								11,064		11,041	23	0
Other comprehensive income attributable to noncontrolling interests		483	459																																				460
Adjustments to Additional Paid in Capital, Share-based Compensation, Other Long-term Incentive Plans, Requisite Service Period Recognition		(3)			0	0	(449)	446		0	0	(3)	0	0	0
Restricted stock issued, net of amortization	4,121	4,121			0	1	0	4,120		0	0	4,121	0	0	0																							4,121	0	0	0	4,121
Common stock redeemed for taxes withheld for stock based compensation, net																											6,643	0	0	0	6,643	0	0	6,643	0	0	0
Stock Repurchased and Retired During Period, Value																											(124,989)	0	(21)	0	(124,968)	0		(124,989)	0	0	0
Common stock issued under dividend reinvestment plan		358	$ 358																								358	0	0	0	358	0	0	358	0	0	0
Common stock issued, net of issuance costs																											$ 10	$ 0	$ 0	$ 0	$ 10	$ 0	$ 0	$ 10	$ 0	$ 0	$ 0
Distributions to partners	(96,419)	(1,018)			0	0	0	0		0	0	0	0	(1,018)	(1,018)																							(95,401)	(1,018)	0	(194)	(95,207)
Common units redeemed as a result of common stock redeemed by Parent Company, net of issuances	$ 6,275																																					6,275	0	0	0	6,275
Preferred stock		0
Cash dividends declared - common stock/unit		95,401			0	0	0	0		0	95,207	95,207	194	0	194
Ending Balance at Mar. 31, 2018		$ 6,605,381			$ 0	$ 1,694	$ (18,756)	$ 7,746,427		$ 4,764	$ (1,169,828)	$ 6,564,301	$ 10,847	$ 30,233	$ 41,080																							$ 6,575,148	$ 30,233	$ 4,764	$ 10,847	$ 6,559,537