Consolidated Statement of Changes in Equity (USD $) In Thousands, except Per Share data, unless otherwise specified	Total	Parent Company [Member]	Partnership Interest [Member]	Preferred Stock Parent Company [Member]	Common Stock Parent Company [Member]	Treasury Stock Parent Company [Member]	Additional Paid In Capital Parent Company [Member]	Accumulated Other Comprehensive Loss	Accumulated Other Comprehensive Loss Parent Company [Member]	Accumulated Other Comprehensive Loss Partnership Interest [Member]	Partners Capital Total [Member] Partnership Interest [Member]	Distributions in Excess of Net Income Parent Company [Member]	Preferred Units Partnership Interest [Member]	General Partner Preferred and Common Units Partnership Interest [Member]	Limited Partners [Member] Partnership Interest [Member]	Total Stockholders' Equity [Member] Parent Company [Member]	Noncontrolling Interests Preferred Units [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]	Preferred Units [Member] Accumulated Other Comprehensive Loss Partnership Interest [Member]	Preferred Units [Member] Partners Capital Total [Member] Partnership Interest [Member]	Preferred Units [Member] Preferred Units Partnership Interest [Member]	Preferred Units [Member] General Partner Preferred and Common Units Partnership Interest [Member]	Preferred Units [Member] Limited Partners [Member] Partnership Interest [Member]	Preferred Units [Member] Noncontrolling Interests in Limited Partners Interest in Consolidated Partnerships [Member] Partnership Interest [Member]	Preferred Stock Parent Company [Member]	Preferred Stock Common Stock Parent Company [Member]	Preferred Stock Treasury Stock Parent Company [Member]	Preferred Stock Additional Paid In Capital Parent Company [Member]	Preferred Stock Accumulated Other Comprehensive Loss Parent Company [Member]	Preferred Stock Distributions in Excess of Net Income Parent Company [Member]	Preferred Stock Total Stockholders' Equity [Member] Parent Company [Member]	Preferred Stock Noncontrolling Interests Preferred Units [Member] Parent Company [Member]	Preferred Stock Noncontrolling Interest Exchangeable Operating Partnership Units [Member] Parent Company [Member]	Preferred Stock Noncontrolling Interests in Limited Partners Interest in Consolidated Partnerships [Member] Parent Company [Member]	Preferred Stock Total Noncontrolling Interests [Member] Parent Company [Member]	Common Stock Parent Company [Member]	Common Stock Preferred Stock Parent Company [Member]	Common Stock Parent Company [Member]	Common Stock Treasury Stock Parent Company [Member]	Common Stock Additional Paid In Capital Parent Company [Member]	Common Stock Accumulated Other Comprehensive Loss Parent Company [Member]	Common Stock Distributions in Excess of Net Income Parent Company [Member]	Common Stock Total Stockholders' Equity [Member] Parent Company [Member]	Common Stock Noncontrolling Interests Preferred Units [Member] Parent Company [Member]	Common Stock Noncontrolling Interest Exchangeable Operating Partnership Units [Member] Parent Company [Member]	Common Stock Noncontrolling Interests in Limited Partners Interest in Consolidated Partnerships [Member] Parent Company [Member]	Common Stock Total Noncontrolling Interests [Member] Parent Company [Member]	Noncontrolling Interest Exchangeable Operating Partnership Units [Member] Total Noncontrolling Interests [Member] Parent Company [Member]	Noncontrolling Interests Preferred Units [Member] Parent Company [Member]
Beginning balance at Dec. 31, 2011		$ (1,869,654)	$ (1,869,654)	$ (275,000)	$ (899)	$ 15,197	$ (2,281,817)		$ 71,429		$ (1,856,550)	$ 662,735		$ (1,879,784)		$ (1,808,355)	$ (49,158)	$ 963	$ (13,104)		$ (61,299)
Common stock/unit per share	$ 1.85
Net proceeds from common stock issuance																																								21,542
Other comprehensive income:
Net income		26,209	26,209	0	0	0	0		0		25,344			25,867		25,867	(629)	106	865
Net Income (Loss) Attributable to Parent		25,867	25,344
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax		(25)	(25)
Current period other comprehensive income, net		13,711	13,711	0	0	0	0	13,711	13,714		13,742	0		0		13,714	0	28	(31)
Other Comprehensive (Income) Loss, Net of Tax, Portion Attributable to Noncontrolling Interest		(3)	(31)
Deferred compensation plan		12	12	0	0	273	(261)		0		12	0		12		12	0	0	0		0
Restricted stock issued, net of amortization		11,526		0	0	0	11,526		0	0		0	0		0	11,526	0	0	0	0	0
Common stock redeemed for taxes withheld for stock based compensation, net				0	0	0											0	0																						(1,474)				(1,474)	0	0	(1,474)			0	0
Stock Redeemed or Called During Period, Value		(275,000)	275,000	(275,000)	0	0	(9,277)		0	0	275,000	(9,277)	0	275,000	0	(275,000)	0	0	0	0	0
Stock Issued During Period, Value, Dividend Reinvestment Plan				0	0	0											0	0																						988				988	0	0	988			0	0
Common stock issued for stock offerings, net of issuance costs		21,542	(313,900)	0	(5)	0				0	(313,900)		0	(313,900)	0		0	0		0									(325,000)	0	0	(11,100)	0	0	(313,900)	0	0	0	0					(21,537)	0	0	(21,542)			0	0
Common stock issued for partnership units exchanged		0	0
Net proceeds from issuance of preferred stock		313,900	313,900
Partners' Capital Account, Redemptions		(48,125)		0	0	0	0		0			0				0	(48,125)	0	0		(48,125)	(48,125)	0	(48,125)	(48,125)	0	0	0
Contributions from partners		3,362	3,362	0	0	0	0		0		0	0		0		0	0	0	3,362		3,362
Distributions To Partners		(1,001)	166,736	0	0	0	0		0	0	165,735	0	0	165,411	324	0	0	0	(1,001)	1,001	(1,001)
Cash dividends declared:
Preferred stock/unit		(23,658)	23,658	0	0	0	0		0	0	23,658		(404)	23,254	0	(23,254)	(404)	0	0	0	(404)
Preferred stock dividends		(32,531)
Common stock/unit		(165,735)		0	0	0	0		0			(165,411)				(165,411)	0	(324)	0		(324)
Restricted Stock Issued By Parent Company Net Of Amortization			11,526								11,526			11,526
Common unit issued as a result of common stock issued by Parent Company, net of purchases			(21,056)							0	(21,056)		0	(21,056)	0					0
Common units exchanged for common stock of the parent company			0							0	0		0	0	0					0
Ending Balance at Dec. 31, 2012		(1,745,911)	(1,745,911)	(325,000)	(904)	14,924	(2,312,310)		57,715	57,715	(1,729,612)	834,810	0	(1,788,480)	1,153	(1,730,765)	0	1,153	(16,299)	(16,299)	(15,146)
Common stock/unit per share	$ 1.85
Net proceeds from common stock issuance	101,342
Other comprehensive income:
Net income		151,285	151,285	0	0	0	0		0		150,080			149,804		149,804	0	276	1,205
Net Income (Loss) Attributable to Parent		149,804	150,080
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax		33	33
Current period other comprehensive income, net		40,418	40,418	0	0	0	0	40,418	40,311		40,386	0		0		40,311	0	75	32
Other Comprehensive (Income) Loss, Net of Tax, Portion Attributable to Noncontrolling Interest		107	32
Deferred compensation plan		0		0	0	(1,802)	1,802		0			0				0	0	0	0		0
Restricted stock issued, net of amortization		14,141		0	0	0	14,141		0	0		0	0		0	14,141	0	0	0	0	0
Common stock redeemed for taxes withheld for stock based compensation, net																																								(2,887)	0	0	0	(2,887)	0	0	(2,887)	0	0	0	0
Stock Issued During Period, Value, Dividend Reinvestment Plan																																								1,075	0	0	0	1,075	0	0	1,075	0	0	0	0
Common stock issued for stock offerings, net of issuance costs		99,753																																						(99,753)	0	(19)	0	(99,734)	0	0	(99,753)	0	0	0	0
Common stock issued for partnership units exchanged		(302)	(302)																																					0	0	0	0	(302)	0	0	(302)	0	(302)	0	(302)
Net proceeds from issuance of preferred stock		0	0
Partners' Capital Account, Redemptions																						0	0	0	0	0	0	0
Contributions from partners		5,792	5,792	0	0	0	0		0		0	0		0		0	0	0	5,792		5,792
Distributions To Partners		(4,122)	173,292	0	0	0	0		0	0	169,170	0	0	168,848	322	0	0	0	(4,122)	4,122	(4,122)
Cash dividends declared:
Preferred stock/unit		(21,062)	21,062	0	0	0	0		0	0	21,062	21,062	0	21,062	0	(21,062)		0	0	0	0																																0
Preferred stock dividends		(21,062)
Common stock/unit		(169,170)		0	0	0	0		0			(168,848)				(168,848)	0	(322)	0																																	(322)
Restricted Stock Issued By Parent Company Net Of Amortization			14,141								14,141			14,141
Common unit issued as a result of common stock issued by Parent Company, net of purchases			97,941							0	97,941		0	97,941	0					0
Common units exchanged for common stock of the parent company			0							0	0		0	(302)	302					0
Ending Balance at Dec. 31, 2013		(1,861,134)	(1,861,134)	(325,000)	(923)	16,726	(2,426,477)		17,404	17,404	(1,841,928)	874,916	0	(1,860,758)	1,426	(1,843,354)	0	1,426	(19,206)	(19,206)	(17,780)
Common stock/unit per share	$ 1.88
Net proceeds from common stock issuance	103,821
Other comprehensive income:
Net income		188,847	188,847	0	0	0	0		0		187,709			187,390		187,390	0	319	1,138
Net Income (Loss) Attributable to Parent		187,390	187,709
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax		(606)	(606)
Current period other comprehensive income, net		(40,615)	(40,615)	0	0	0	0	(40,615)	(40,344)		(40,414)	0		0		(40,344)	0	(70)	(201)
Other Comprehensive (Income) Loss, Net of Tax, Portion Attributable to Noncontrolling Interest		(271)	(201)
Deferred compensation plan		0		0	0	2,656	2,656		0			0				0	0	0	0		0
Restricted stock issued, net of amortization		12,161		0	0	0	12,161		0	0		0	0		0	12,161	0	0	0	0	0
Common stock redeemed for taxes withheld for stock based compensation, net																																								(3,493)	0	0	0	(3,493)	0	0	(3,493)	0	0	0	0
Stock Issued During Period, Value, Dividend Reinvestment Plan																																								1,184	0	0	0	1,184	0	0	1,184	0	0	0	0
Common stock issued for stock offerings, net of issuance costs		102,453																																						(102,453)	0	(18)	0	(102,435)	0	0	(102,453)	0	0	0	0
Common stock issued for partnership units exchanged		(137)	(137)																																					0	0	0	0	(137)	0	0	(137)	0	(137)	0	(137)
Net proceeds from issuance of preferred stock		0	0
Partners' Capital Account, Redemptions		(300)		0	0	0	0		0			0				0	0	(300)	0		(300)	(300)	0	(300)	0	0	300	0
Contributions from partners		16,204	16,204	0	0	0	0		0		0	0		0		0	0	0	16,204		16,204
Distributions To Partners		(5,947)	180,031	0	0	0	(1,404)		0	0	175,488	0	0	175,188	300	(1,404)	0	0	(4,543)	4,543	(4,543)
Cash dividends declared:
Preferred stock/unit		(21,062)	21,062	0	0	0	0		0	0	21,062		0	21,062	0	(21,062)		0	0	0	0																																0
Preferred stock dividends		(21,062)
Common stock/unit		(174,084)		0	0	0	0		0			(173,784)				(173,784)	0	(300)	0																																	(300)
Restricted Stock Issued By Parent Company Net Of Amortization			12,161								12,161			12,161
Common unit issued as a result of common stock issued by Parent Company, net of purchases			100,144							0	100,144		0	(100,144)	0					0
Common units exchanged for common stock of the parent company			0							0	0		0	(137)	137					0
Ending Balance at Dec. 31, 2014		$ (1,936,482)	$ (1,936,482)	$ (325,000)	$ (941)	$ 19,382	$ (2,540,153)		$ 57,748	$ 57,748	$ (1,904,678)	$ 882,372	$ 0	$ (1,964,340)	$ 1,914	$ (1,906,592)	$ 0	$ 1,914	$ (31,804)	$ (31,804)	$ (29,890)