Consolidated Statement of Equity and Comprehensive Income (Loss) (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] Parent Company [Member]	Accumulated Other Comprehensive Income (Loss) [Member] Partnership Interest [Member]	Accumulated Distributions in Excess of Net Income [Member] Parent Company [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, Class [Domain] Partnership Interest [Member]	General Partner [Member] Partnership Interest [Member]	Limited Partners [Member] Partnership Interest [Member]	Partners Capital Total [Member] Partnership Interest [Member]
Beginning balance at Dec. 31, 2008	$ 1,741,744	$ 1,741,744	$ 275,000	$ 756	$ (133,046)	$ 1,781,557	$ (90,689)	$ (90,689)	$ (157,255)	$ 1,676,323	$ 49,158	$ 8,283	$ 7,980	$ 7,980	$ 65,421	$ 49,158	$ 1,767,012	$ 8,283	$ 1,733,764
Comprehensive Income:
Net income	(29,036)	(29,036)	0	0	0	0	0	0	(32,997)	(32,997)	3,725	(216)	452	452	3,961	3,725	(32,997)	(216)	(29,488)
Amortization of loss on derivative instruments	(2,305)	(2,305)	0	0	0	0	(2,292)	(2,292)	0	(2,292)	0	(13)	0	0	(13)	0	0	(13)	(2,305)
Change In Fair Value Of Derivative Instruments Net Of Settlement	38,645	38,645	0	0	0	0	38,424	38,424	0	38,424	0	221		0	221	0	0	221	38,645
Total comprehensive income	11,914	11,914								7,719					4,195				11,462
Deferred compensation plan, net	(4,044)	(4,044)	0	0	5,123	(1,079)	0	0	0	(4,044)	0	0	0	0	0	0	(4,044)	0	(4,044)
Restricted stock issued, net of amortization	5,963		0	2	0	5,961	0		0	5,963	0	0	0		0
Common stock redeemed for taxes withheld for stock based compensation, net	343		0	0	0	343	0		0	343	0	0	0		0
Common stock issued for dividend reinvestment plan	3,223		0	1	0	3,222	0		0	3,223	0	0	0		0
Common stock issued for partnership units exchanged	0	0
Common stock issued for stock offerings, net of issuance costs			0	112	0	345,685	0		0		0	0	0
Treasury Stock, Retired, Cost Method, Amount	0		0	(56)	111,414	(111,358)	0		0	0	0	0	0		0
Contributions from partners	4,197	4,197	0	0	0	0	0	0	0	0	0	0	4,197	4,197	4,197	0	0	0	0
Distributions to partners	881	(163,770)	0	0	0	0	0	0	0	0	0	0	881	(881)	881	0	(161,909)	(980)	(162,889)
Preferred unit distributions		(23,400)						0						0		(3,725)	(19,675)	0	(23,400)
Restricted stock issued by Parent Company, net of amortization		5,963						0						0		0	5,963	0	5,963
Common units issued as a result of common stock issued by Parent Company, net of repurchases		349,915						0						0		0	349,915	0	349,915
Cash dividends declared:
Preferred stock/unit	23,400		0	0	0	0	0		19,675	19,675	3,725	0	0		3,725
Common stock/unit ($1.3875 per share)	162,889		0	0	0	0	0		161,909	161,909	0	980	0		980
Ending Balance at Dec. 31, 2009	1,930,607	1,930,607	275,000	815	(16,509)	2,024,883	(49,973)	(49,973)	(371,836)	1,862,380	49,158	7,321	11,748	11,748	68,227	49,158	1,912,353	7,321	1,918,859
Comprehensive Income:
Net income	13,001	13,001	0	0	0	0	0	0	8,816	8,816	3,725	84	376	376	4,185	3,725	8,816	84	12,625
Amortization of loss on derivative instruments	(5,575)	(5,575)	0	0	0	0	(5,563)	(5,563)	0	(5,563)	0	(12)	0	0	(12)	0	0	(12)	(5,575)
Change In Fair Value Of Derivative Instruments Net Of Settlement	(36,556)	(36,556)	0	0	0	0	(36,475)	(36,475)	0	(36,475)	0	(81)	0	0	(81)	0	0	(81)	(36,556)
Total comprehensive income	(17,980)	(17,980)								(22,096)					4,116				(18,356)
Deferred compensation plan, net	273	273	0	0	(334)	607	0	0	0	273	0	0	0	0	0	0	273	0	273
Restricted stock issued, net of amortization	7,236		0	0	0	7,236	0		0	7,236	0	0	0		0
Common stock redeemed for taxes withheld for stock based compensation, net	(1,374)		0	0	0	(1,374)	0		0	(1,374)	0	0	0		0
Common stock issued for dividend reinvestment plan	1,848		0	1	0	1,847	0		0	1,848	0	0	0		0
Common stock issued for partnership units exchanged	7,630	7,630
Common stock issued for stock offerings, net of issuance costs	0		0	3	0	7,627	0		0	7,630	0	(7,630)	0		(7,630)
Contributions from partners	161	161	0	0	0	0	0	0	0	0	0	0	161	161	161	0	0	0	0
Distributions to partners	1,456	(152,423)	0	0	0	0	0	0	0	0	0	0	1,456	(1,456)	1,456	0	(150,499)	(468)	(150,967)
Preferred unit distributions		(23,400)						0						0		(3,725)	(19,675)	0	(23,400)
Restricted stock issued by Parent Company, net of amortization		7,236						0						0		0	7,236	0	7,236
Common units issued as a result of common stock issued by Parent Company, net of repurchases		474						0						0		0	474	0	474
Common units exchanged for common stock of Parent Company		0						0						0		0	7,630	(7,630)	0
Cash dividends declared:
Preferred stock/unit	23,400		0	0	0	0	0		19,675	19,675	3,725	0	0		3,725
Common stock/unit ($1.3875 per share)	150,967		0	0	0	0	0		150,499	150,499	0	468	0		468
Ending Balance at Dec. 31, 2010	1,744,402	1,744,402	275,000	819	(16,175)	2,039,612	(80,885)	(80,885)	(533,194)	1,685,177	49,158	(762)	10,829	10,829	59,225	49,158	1,766,062	(762)	1,733,573
Comprehensive Income:
Net income	55,788	55,788	0	0	0	0	0	0	51,370	51,370	3,725	103	590	590	4,418	3,725	51,370	103	55,198
Amortization of loss on derivative instruments		9,467						9,447						0		0	0	20	9,467
Change In Fair Value Of Derivative Instruments Net Of Settlement	18		0	0	0	0	9		0	9	0	0	9		9
Total comprehensive income	65,273	65,273								60,826					4,447				64,674
Deferred compensation plan, net	(17,843)	(17,843)	0	0	978	16,865	0	0	0	(17,843)	0	0	0	0	0	0	(17,843)	0	(17,843)
Restricted stock issued, net of amortization	10,659		0	0	0	10,659	0		0	10,659	0	0	0		0
Common stock redeemed for taxes withheld for stock based compensation, net	(1,689)		0	0	0	(1,689)	0		0	(1,689)	0	0	0		0
Common stock issued for dividend reinvestment plan	1,081		0	0	0	1,081	0		0	1,081	0	0	0		0
Common stock issued for partnership units exchanged	0	0
Common stock issued for stock offerings, net of issuance costs	215,369		0	80	0	215,289	0		0	215,369	0	0	0		0
Contributions from partners	2,787	2,787	0	0	0	0	0	0	0	0	0	0	2,787	2,787	2,787	0	0	0	0
Distributions to partners	1,111	(162,671)	0	0	0	0	0	0	0	0	0	0	(1,111)	(1,111)	1,111	0	(161,236)	(324)	(161,560)
Preferred unit distributions		(23,400)						0						0		(3,725)	(19,675)	0	(23,400)
Restricted stock issued by Parent Company, net of amortization		10,659						0						0		0	10,659	0	10,659
Common units issued as a result of common stock issued by Parent Company, net of repurchases		214,761						0						0		0	214,761	0	214,761
Cash dividends declared:
Preferred stock/unit	23,400		0	0	0	0	0		(19,675)	19,675	(3,725)	0	0		3,725
Common stock/unit ($1.3875 per share)	161,560		0	0	0	0	0		(161,236)	161,236	0	(324)	0		324
Ending Balance at Dec. 31, 2011	$ 1,869,654	$ 1,869,654	$ 275,000	$ 899	$ (15,197)	$ 2,281,817	$ (71,429)	$ (71,429)	$ (662,735)	$ 1,808,355	$ 49,158	$ (963)	$ 13,104	$ 13,104	$ 61,299	$ 49,158	$ 1,879,784	$ (963)	$ 1,856,550