Consolidated Statement of Changes in Equity (USD $) In Thousands, unless otherwise specified	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] 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	25,056	25,056	0	0	0	0		0	0		24,655	42	359	359	401		24,655	42	24,697
Net Income (Loss) Attributable to Parent	24,655	24,697
Current period other comprehensive income, net	(11,281)	(11,281)	0	0	0	0	(11,281)	(11,195)	(11,195)	0	(11,195)	(20)	(66)				0	(20)	(11,215)
Other comprehensive loss attributable to noncontrolling interests	(86)	(66)
Adjustments to Additional Paid in Capital, Share-based Compensation, Other Long-term Incentive Plans, Requisite Service Period Recognition	0		0	0	(1,625)	1,625		0		0	0	0	0		0
Restricted stock issued, net of amortization	2,915	2,915	0	0	0	2,915		0	0	0	2,915	0	0	0	0		2,915	0	2,915
Common stock redeemed for taxes withheld for stock based compensation, net																				3,164	0	0	0	3,164	0	0	3,164	0	0	0
Common stock issued for dividend reinvestment plan	313	313																			0	0	0	313	0	0	313	0	0	0
Preferred unit distributions		(5,266)							0					0			(5,266)	0	(5,266)
Contributions from partners	15,443	15,443	0	0	0	0		0	0	0	0	0	15,443	15,443	15,443		0	0	0
Distributions to partners	(426)	(43,764)	0	0	0	0		0	0	0	0	0	(426)	(426)	(426)		(43,260)	(78)	(43,338)
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		(2,851)							0					0			(2,851)	0	(2,851)
Redemption of partnership units	300		0	0	0	0		0		0	0	300	0		300
Cash dividends declared: preferred stock/unit	5,266		0	0	0	0		0		5,266	5,266	0	0		0
Preferred Stock Dividends, Income Statement Impact	5,266
Cash dividends declared - common stock/unit	43,338		0	0	0	0		0		43,260	43,260	78	0		78
Ending Balance at Mar. 31, 2014	1,841,086	1,841,086	325,000	923	(18,351)	2,428,166		(28,599)	(28,599)	(898,787)	1,808,352	(1,782)	34,516	34,516	32,734		1,836,951	(1,782)	1,806,570
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	30,992	30,992	0	0	0	0		0	0		30,440	49	503	503	552		30,440	49	30,489
Net Income (Loss) Attributable to Parent	30,440	30,489
Current period other comprehensive income, net	(11,633)	(11,633)	0	0	0	0	(11,633)	(11,529)	(11,529)	0	(11,529)	(18)	(86)				0	(18)	(11,547)
Other comprehensive loss attributable to noncontrolling interests	(104)	(86)
Adjustments to Additional Paid in Capital, Share-based Compensation, Other Long-term Incentive Plans, Requisite Service Period Recognition	0		0	0	(1,256)	1,256		0		0	0	0	0		0
Restricted stock issued, net of amortization	3,548	3,548	0	2	0	3,546		0	0	0	3,548	0	0	0	0		3,548	0	3,548
Common stock redeemed for taxes withheld for stock based compensation, net																				9,850	0	0	0	9,850	0	0	9,850	0	0	0
Common stock issued for dividend reinvestment plan	374	374																			0	0	0	374	0	0	374	0	0	0
Common stock issued for stock offerings, net of issuance costs																				(992)	0	0	0	992	0	0	992	0	0	0
Preferred unit distributions		(5,266)							0					0			(5,266)	0	(5,266)
Contributions from partners	13	13	0	0	0	0		0	0	0	0	0	13	13	13		0	0	0
Distributions to partners	(1,050)	(46,773)	0	0	0	0		0	0	0	0	0	(1,050)	(1,050)	(1,050)		(45,647)	(76)	(45,723)
Common units issued as a result of common stock issued by Parent Company, net of repurchases		(8,484)							0					0			(8,484)	0	(8,484)
Cash dividends declared: preferred stock/unit	5,266		0	0	0	0		0			5,266	0	0		0
Preferred Stock Dividends, Income Statement Impact	5,266
Cash dividends declared - common stock/unit	45,723		0	0	0	0		0		45,647	45,647	76	0		76
Ending Balance at Mar. 31, 2015	$ 1,898,879	$ 1,898,879	$ 325,000	$ 943	$ (20,638)	$ 2,536,471		$ (69,277)	$ (69,277)	$ (902,845)	$ 1,869,654	$ (1,959)	$ 31,184	$ 31,184	$ 29,225		$ 1,938,931	$ (1,959)	$ 1,867,695