Consolidated Statement of Changes in Equity - USD ($) shares in Thousands, $ in Thousands	Parent Company [Member]	Partnership Interest [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]	Accumulated Other Comprehensive Income (Loss) [Member] Partnership Interest [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 Interests in Limited Partners' Interest in Consolidated Partnerships [Member] Partnership Interest [Member]	Total Noncontrolling Interests [Member] Parent Company [Member]	General Partner Preferred and Common Units [Member] Partnership Interest [Member]	Limited Partners [Member] Partnership Interest [Member]	Total Partners' Capital [Member] Partnership Interest [Member]	Preferred Units [Member] Accumulated Other Comprehensive Income (Loss) [Member] Partnership Interest [Member]	Preferred Units [Member] Noncontrolling Interests in Limited Partners' Interest in Consolidated Partnerships [Member] Partnership Interest [Member]	Preferred Units [Member] General Partner Preferred and Common Units [Member] Partnership Interest [Member]	Preferred Units [Member] Limited Partners [Member] Partnership Interest [Member]	Preferred Units [Member] Total Partners' Capital [Member] Partnership Interest [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] Total Noncontrolling Interests [Member] Parent Company [Member]
Beginning balance at Dec. 31, 2014	$ 1,936,482	$ 1,936,482	$ 325,000	$ 941	$ (19,382)	$ 2,540,153		$ (57,748)	$ (57,748)	$ (882,372)	$ 1,906,592	$ (1,914)	$ 31,804	$ 31,804	$ 29,890	$ 1,964,340	$ (1,914)	$ 1,904,678
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	69,271	69,271	0	0	0	0		0	0		68,184	110	977	977	1,087	68,184	110	68,294
Net Income (Loss) Attributable to Parent	68,184	68,294
Current period other comprehensive income, net	8,964	8,964	0	0	0	0	$ 8,949	8,949	8,949	0	8,949	15	0			0	15	8,964
Other comprehensive (loss) income attributable to noncontrolling interests	15	0
Adjustments to Additional Paid in Capital, Share-based Compensation, Other Long-term Incentive Plans, Requisite Service Period Recognition	0		0	0	(8)	8		0		0	0	0	0		0
Restricted stock issued, net of amortization	7,004	7,004	0	3	0	7,001		0	0	0	7,004	0	0	0	0	7,004	0	7,004
Common stock redeemed for taxes withheld for stock based compensation, net																								$ 9,793	$ 0	$ 1	$ 0	$ 9,792	$ 0	$ 0	$ 9,793	$ 0	$ 0	$ 0
Common stock issued for dividend reinvestment plan	683	683																							0	0	0	683	0	0	683	0	0	0
Common stock issued for stock offerings, net of issuance costs			0	0	0	955		0		0	955	0	0		0
Contributions from partners	256	256	0	0	0	0		0	0	0	0	0	256	256	256	0	0	0
Distributions to partners	(1,965)	(93,424)	0	0	0	0		0	0	0	0	0	(1,965)	(1,965)	(1,965)	(91,308)	(151)	(91,459)
Cash dividends declared: preferred stock/unit	10,531	10,531	0	0	0	0		0		10,531	10,531	0	0		0				$ 0	$ 0	$ 10,531	$ 0	$ 10,531
Preferred Stock Dividends, Income Statement Impact	10,531
Cash dividends declared - common stock/unit	91,459		0	0	0	0		0		91,308	91,308	151	0		151
Ending Balance at Jun. 30, 2015	1,909,867	$ 1,909,867	325,000	943	(19,390)	2,539,008		(48,799)	$ (48,799)	(916,027)	1,880,735	(1,940)	31,072	$ 31,072	29,132	$ 1,929,534	$ (1,940)	$ 1,878,795
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Partners' Capital Account, Units, Redeemed		8,155							0					0		8,155	0	8,155
Beginning balance at Dec. 31, 2015	2,082,620	$ 2,082,620	325,000	972	(19,658)	2,742,508		(58,693)	$ (58,693)	(936,020)	2,054,109	(1,975)	30,486	$ 30,486	28,511	$ 2,112,802	$ (1,975)	$ 2,052,134
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	94,221	94,221	0	0	0	0		0	0		93,218	150	853	853	1,003	93,218	150	93,368
Net Income (Loss) Attributable to Parent	93,218	93,368
Current period other comprehensive income, net	(21,642)	(21,642)	0	0	0	0	$ (21,345)	(21,345)	(21,345)	0	(21,345)	(34)	(263)			0	(34)	(21,379)
Other comprehensive (loss) income attributable to noncontrolling interests	(297)	(263)
Adjustments to Additional Paid in Capital, Share-based Compensation, Other Long-term Incentive Plans, Requisite Service Period Recognition	0		0	0	2,815	(2,815)		0		0	0	0	0		0
Restricted stock issued, net of amortization	6,804	6,804	0	2	0	6,802		0	0	0	6,804	0	0	0	0	6,804	0	6,804
Common stock redeemed for taxes withheld for stock based compensation, net																								7,876	0	0	0	7,876	0	0	7,876	0	0	0
Common stock issued for dividend reinvestment plan	547	547																							0	0	0	547	0	0	547	0	0	0
Common stock issued for stock offerings, net of issuance costs																								$ 149,788	$ 0	$ 21	$ 0	$ 149,767	$ 0	$ 0	$ 149,788	$ 0	$ 0	$ 0
Contributions from partners	8,600	8,600	0	0	0	0		0	0	0	0	0	8,600	8,600	8,600	0	0	0
Distributions to partners	(2,744)	(100,506)	0	0	0	(350)		0	0	0	(350)	0	(2,394)	(2,394)	(2,394)	97,958	(154)	(98,112)
Common units redeemed as a result of common stock redeemed by Parent Company, net of issuances		142,459							0					0		142,459	0	142,459
Cash dividends declared: preferred stock/unit	10,531	10,531	0	0	0	0		0			10,531	0	0		0				$ 0	$ 0	$ 10,531	$ 0	$ 10,531
Preferred Stock Dividends, Income Statement Impact	10,531
Cash dividends declared - common stock/unit	97,762		0	0	0	0		0		97,608	97,608	154	0		154
Ending Balance at Jun. 30, 2016	$ 2,202,025	$ 2,202,025	$ 325,000	$ 995	$ (16,843)	$ 2,888,583		$ (80,038)	$ (80,038)	$ (950,941)	$ 2,166,756	$ (2,013)	$ 37,282	$ 37,282	$ 35,269	$ 2,246,794	$ (2,013)	$ 2,164,743