Consolidated Statement of Changes in Equity - USD ($) $ in Thousands	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]	General Partner Preferred and Common Units Partnership Interest [Member]	Limited Partners [Member] Partnership Interest [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]	Preferred Units [Member] Accumulated Other Comprehensive Loss Partnership Interest [Member]	Preferred Units [Member] Partners Capital Total [Member] 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]	Common Stock Parent Company [Member]	Common Stock Preferred Stock Parent Company [Member]	Common Stock 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 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]
Common stock/unit per share	$ 1.85
Net proceeds from common stock issuance		$ 99,753																								$ 99,753
Beginning balance at Dec. 31, 2012		(1,745,911)	$ (1,745,911)	$ (325,000)	$ (904)	$ 14,924	$ (2,312,310)		$ 57,715		$ (1,729,612)	$ 834,810	$ (1,788,480)		$ (1,730,765)	$ 1,153	$ (16,299)		$ (15,146)
Other comprehensive income:
Net income		151,285	151,285	0	0	0	0		0		150,080		149,804		149,804	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		(9,433)	(9,433)
Current period other comprehensive income, net		40,418	40,418	0	0	0	0	$ 40,418	40,311		40,386	0	0		40,311	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
Restricted stock issued, net of amortization		14,141		0	0	0	14,141		0	$ 0		0		$ 0	14,141	0	0	$ 0	0
Common stock redeemed for taxes withheld for stock based compensation, net				0	0	0										0										(2,887)				$ (2,887)	$ 0	$ 0	$ (2,887)		$ 0	$ 0
Stock Issued During Period, Value, Dividend Reinvestment Plan				0	0	0										0										1,075				1,075	0	0	1,075		0	0
Common stock issued for stock offerings, net of issuance costs				0	(19)	0										0														(99,734)	0	0	(99,753)		0	0
Common stock issued for partnership units exchanged		(302)	(302)																							0	$ 0	$ 0	$ 0	(302)	0	0	(302)	$ (302)	0	(302)
Contributions from partners		5,792	5,792	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	168,848	322	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	21,062	0	(21,062)	0	0	0	0
Preferred stock dividends		(21,062)
Common stock/unit		(169,170)		0	0	0	0		0			(168,848)			(168,848)	(322)	0		(322)
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	(1,860,758)	1,426	(1,843,354)	1,426	(19,206)	(19,206)	(17,780)
Cash dividends declared:
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)		(97,941)	0				0
Common units exchanged for common stock of the parent company			0							0	0		(302)	302				0
Common stock/unit per share	$ 1.88
Net proceeds from common stock issuance	$ 103,821	102,453
Net income		188,847	188,847	0	0	0	0		0		187,709		187,390		187,390	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		(9,353)	(9,353)
Current period other comprehensive income, net		(40,615)	(40,615)	0	0	0	0	(40,615)	(40,344)		(40,414)	0	0		(40,344)	(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
Restricted stock issued, net of amortization		12,161		0	0	0	12,161		0	0		0		0	12,161	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
Stock Issued During Period, Value, Dividend Reinvestment Plan																										1,184	0	0	0	1,184	0	0	1,184	0	0	0
Common stock issued for stock offerings, net of issuance costs																										(102,453)	0	(18)	0	(102,435)	0	0	(102,453)	0	0	0
Common stock issued for partnership units exchanged		(137)	(137)																							0	0	0	0	(137)	0	0	(137)	(137)	0	(137)
Partners' Capital Account, Redemptions		(300)		0	0	0	0		0			0			0	(300)	0		(300)	$ (300)	$ 0	$ (300)	$ 0	$ (300)	$ 0
Contributions from partners		16,204	16,204	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	175,188	300	(1,404)	0	(4,543)	4,543	(4,543)
Preferred stock/unit		(21,062)	(21,062)								21,062	21,062	21,062	0	(21,062)	0	0	0	0
Preferred stock dividends		(21,062)
Common stock/unit		(174,084)		$ 0	$ 0	$ 0	$ 0		$ 0			(173,784)			(173,784)	(300)	0																				$ (300)
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	(1,964,340)	1,914	(1,906,592)	1,914	(31,804)	(31,804)	(29,890)
Cash dividends declared:
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		100,144	0				0
Common units exchanged for common stock of the parent company			0							0	0		(137)	137				0
Common stock/unit per share	$ 1.94
Net proceeds from common stock issuance	$ 12,843	198,494
Net income		152,543	152,543	0	0	0	0		0		150,296		150,056		150,056	240	2,247
Net Income (Loss) Attributable to Parent		150,056	150,296
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax		(9,152)	(9,152)
Current period other comprehensive income, net		(980)	(980)	0	0	0	0	$ (980)	(945)		(947)	0	0		(945)	(2)	(33)
Other Comprehensive (Income) Loss, Net of Tax, Portion Attributable to Noncontrolling Interest		(35)	(33)
Deferred compensation plan		0		0	0	276	276		0			0			0	0	0		0
Restricted stock issued, net of amortization		13,869		0	0	0	13,869		0	0		0		0	13,869	0	0	0	0
Common stock redeemed for taxes withheld for stock based compensation, net																										(9,706)	0	0	0	(9,706)	0	0	(9,706)	0	0	0
Stock Issued During Period, Value, Dividend Reinvestment Plan																										1,250	0	0	0	1,250	0	0	1,250	0	0	0
Common stock issued for stock offerings, net of issuance costs																										$ (198,494)	$ 0	$ (31)	$ 0	$ (198,463)	$ 0	$ 0	$ (198,494)	$ 0	$ 0	$ 0
Common stock issued for partnership units exchanged		0	0
Contributions from partners		717	717	0	0	0	0		0		0	0	0		0	0	717		717
Distributions To Partners		(6,046)	188,987	0	0	0	(1,797)		0	0	184,738	0	184,439	299	(1,797)	0	(4,249)	4,249	(4,249)
Preferred stock/unit		(21,062)	(21,062)	0	0	0	0		0	0	21,062		21,062	0	(21,062)	0	0	0	0
Preferred stock dividends		(21,062)
Common stock/unit		(182,941)		0	0	0	0		0			(182,642)			(182,642)	(299)	0																				$ (299)
Ending Balance at Dec. 31, 2015		$ (2,082,620)	(2,082,620)	$ (325,000)	$ (972)	$ 19,658	$ (2,742,508)		$ 58,693	58,693	(2,052,134)	$ 936,020	(2,112,802)	1,975	$ (2,054,109)	$ 1,975	$ (30,486)	(30,486)	$ (28,511)
Cash dividends declared:
Restricted Stock Issued By Parent Company Net Of Amortization			13,869								13,869		13,869
Common unit issued as a result of common stock issued by Parent Company, net of purchases			$ 190,038							$ 0	$ 190,038		$ (190,038)	$ 0				$ 0