Consolidated Statement of Changes in Equity - USD ($) $ 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]	Preferred Units [Member] Partnership Interest [Member]	General Partner Preferred and Common Units [Member] Partnership Interest [Member]	Limited Partners [Member] Partnership Interest [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, 2013	$ 1,861,134	$ 1,861,134	$ 325,000	$ 923	$ (16,726)	$ 2,426,477		$ (17,404)	$ (17,404)	$ (874,916)	$ 1,843,354	$ (1,426)	$ 19,206	$ 19,206	$ 17,780		$ 1,860,758	$ (1,426)	$ 1,841,928
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	56,217	56,217	0	0	0	0		0	0		55,403	95	719	719	814		55,403	95	55,498
Net Income (Loss) Attributable to Parent	55,403	55,498
Current period other comprehensive income, net	(19,202)	(19,202)	0	0	0	0	$ (19,202)	(19,008)	(19,008)	0	(19,008)	(34)	(160)				0	(34)	(19,042)
Other comprehensive income (loss) attributable to noncontrolling interests	(194)	(160)
Adjustments to Additional Paid in Capital, Share-based Compensation, Other Long-term Incentive Plans, Requisite Service Period Recognition	0		0	0	(2,226)	2,226		0		0	0	0	0		0
Restricted stock issued, net of amortization	5,831	5,831	0	0	0	5,831		0	0	0	5,831	0	0	0	0		5,831	0	5,831
Common stock redeemed for taxes withheld for stock based compensation, net																				$ 3,210	$ 0	$ 0	$ 0	$ 3,210	$ 0	$ 0	$ 3,210	$ 0	$ 0	$ 0
Common stock issued for dividend reinvestment plan	604	604																			0	0	0	604	0	0	604	0	0	0
Preferred unit distributions		(10,531)							0					0			(10,531)	0	(10,531)
Contributions from partners	15,551	15,551	0	0	0	0		0	0	0	0	0	15,551	15,551	15,551		0	0	0
Distributions to partners	(1,008)	(87,692)	0	0	0	0		0	0	0	0	0	(1,008)	(1,008)	(1,008)		(86,532)	(152)	(86,684)
Preferred Stock Redemption Premium		(300)							0					0		$ 0	(300)		(300)
Common units issued as a result of common stock issued by Parent Company, net of repurchases		(2,606)							0					0			(2,606)	0	(2,606)
Redemption of partnership units	300		0	0	0	0		0		0	0	300	0		300
Cash dividends declared: preferred stock/unit	10,531		0	0	0	0		0		10,531	10,531	0	0		0
Preferred Stock Dividends, Income Statement Impact	10,531
Cash dividends declared - common stock/unit	86,684		0	0	0	0		0		86,532	86,532	152	0		152
Ending Balance at Jun. 30, 2014	1,818,402	1,818,402	325,000	923	(18,952)	2,431,928		(36,412)	(36,412)	(916,576)	1,785,911	(1,817)	34,308	34,308	32,491		1,822,323	(1,817)	1,784,094
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	$ 8,964	8,949	8,949	0	8,949	15	0				0	15	8,964
Other comprehensive income (loss) 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																				$ (955)	$ 0	$ 0	$ 0	$ 955	$ 0	$ 0	$ 955	$ 0	$ 0	$ 0
Preferred unit distributions		(10,531)							0					0			(10,531)	0	(10,531)
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)
Common units issued as a result of common stock issued by Parent Company, net of repurchases		(8,155)							0					0			(8,155)	0	(8,155)
Cash dividends declared: preferred stock/unit	10,531		0	0	0	0		0			10,531	0	0		0
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