Consolidated Statement of Equity and Comprehensive Income (Loss) (USD $) In Thousands	Parent Company [Member]	Parent Company [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 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] Total Noncontrolling Interests [Member]	Partnership Interest [Member]	Partnership Interest [Member] Accumulated Other Comprehensive Income (Loss) [Member]	Partnership Interest [Member] Noncontrolling Interests in Limited Partners' Interest in Consolidated Partnerships [Member]	Partnership Interest [Member] Preferred Units, Class [Domain]	Partnership Interest [Member] General Partner [Member]	Partnership Interest [Member] Limited Partners' Capital Account, Class [Domain]	Partnership Interest [Member] Partners Capital Total [Member]
Beginning balance at Dec. 31, 2009	$ 1,930,606	$ 275,000	$ 815	$ (16,509)	$ 2,024,883	$ (49,973)	$ (371,837)	$ 1,862,379	$ 49,158	$ 7,321	$ 11,748	$ 68,227	$ 1,930,606	$ (49,973)	$ 11,748	$ 49,158	$ 1,912,352	$ 7,321	$ 1,918,858
Comprehensive Income:
Net income	45,017	0	0	0	0	0	41,797	41,797	2,794	155	271	3,220	45,017	0	271	2,794	41,797	155	44,746
Amortization of loss on derivative instruments	(3,209)	0	0	0	0	(3,202)	0	(3,202)	0	(7)	0	(7)	(3,209)	(3,202)	0	0	0	(7)	(3,209)
Change In Fair Value Of Derivative Instruments Net Of Settlement	(36,556)	0	0	0	0	(36,472)	0	(36,472)	0	(84)	0	(84)	(36,556)	(36,472)	0	0	0	(84)	(36,556)
Total comprehensive income	11,670							8,527				3,143	11,670						11,399
Deferred compensation plan, net	122	0	0	506	(384)	0	0	122	0	0	0	0	(122)	0	0	0	(122)	0	(122)
Restricted stock issued, net of amortization	5,138	0	0	0	5,138	0	0	5,138	0	0	0	0
Common stock redeemed for taxes withheld for stock based compensation, net	(1,338)	0	0	0	(1,338)	0	0	(1,338)	0	0	0	0
Common stock issued for dividend reinvestment plan	1,594	0	1	0	1,593	0	0	1,594	0	0	0	0
Common stock issued for partnership units exchanged	7,311												7,311
Common stock issued for stock offerings, net of issuance costs	0	0	3	0	7,308	0	0	7,311	0	(7,311)	0	(7,311)
Contributions from partners	161	0	0	0	0	0	0	0	0	0	161	161	161	0	161	0	0	0	0
Distributions to partners	(1,363)	0	0	0	0	0	0	0	0	0	(1,363)	(1,363)	(114,769)	0	(1,363)	0	(113,033)	(373)	(113,406)
Preferred unit distributions													(17,550)	0	0	(2,794)	(14,756)	0	(17,550)
Restricted stock issued by Parent Company, net of amortization													5,138	0	0	0	5,138	0	5,138
Common units issued as a result of common stock issued by Parent Company, net of repurchases													256	0	0	0	256	0	256
Common units exchanged for common stock of Parent Company													0	0	0	0	7,311	(7,311)	0
Cash dividends declared:
Preferred stock/unit	(17,550)	0	0	0	0	0	(14,756)	(14,756)	(2,794)	0	0	(2,794)
Common stock/unit ($1.3875 per share)	(113,406)	0	0	0	0	0	(113,033)	(113,033)	0	(373)	0	(373)
Ending Balance at Sep. 30, 2010	1,815,634	275,000	819	(16,003)	2,037,200	(83,243)	(457,829)	1,755,944	49,158	(285)	10,817	59,690	1,815,634	(83,243)	10,817	49,158	1,839,187	(285)	1,804,817
Beginning balance at Jun. 30, 2010
Comprehensive Income:
Net income	13,873												13,873
Preferred unit distributions													(5,850)
Ending Balance at Sep. 30, 2010	1,815,634												1,815,634
Beginning balance at Dec. 31, 2010	1,744,402	275,000	819	(16,175)	2,039,612	(80,885)	(533,194)	1,685,177	49,158	(762)	10,829	59,225	1,744,402	(80,885)	10,829	49,158	1,766,062	(762)	1,733,573
Comprehensive Income:
Net income	41,608	0	0	0	0	0	38,312	38,312	2,794	77	425	3,296	41,608	0	425	2,794	38,312	77	41,183
Amortization of loss on derivative instruments	(7,099)	0	0	0	0	(7,085)	0	(7,085)	0	(14)	0	(14)	7,099	7,085	0	0	0	14	7,099
Total comprehensive income	48,707							45,397				3,310	48,707						48,282
Deferred compensation plan, net	17,843	0	0	1,147	16,696	0	0	17,843	0	0	0	0	(17,843)	0	0	0	(17,843)	0	(17,843)
Restricted stock issued, net of amortization	8,087	0	0	0	8,087	0	0	8,087	0	0	0	0
Common stock redeemed for taxes withheld for stock based compensation, net	(1,752)	0	0	0	(1,752)	0	0	(1,752)				0
Common stock issued for dividend reinvestment plan	821	0	0	0	821	0	0	821	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	2,646	0	0	0	0	0	0	0	0	0	2,646	2,646	2,646	0	2,646	0	0	0	0
Distributions to partners	(865)	0	0	0	0	0	0	0	0	0	(865)	(865)	(121,099)	0	(865)	0	(119,988)	(246)	(120,234)
Preferred unit distributions													(17,550)	0	0	(2,794)	(14,756)	0	(17,550)
Restricted stock issued by Parent Company, net of amortization													8,087	0	0	0	8,087	0	8,087
Common units issued as a result of common stock issued by Parent Company, net of repurchases													214,438	0	0	0	214,438	0	214,438
Cash dividends declared:
Preferred stock/unit	(17,550)	0	0	0	0	0	(14,756)	(14,756)	(2,794)	0	0	(2,794)
Common stock/unit ($1.3875 per share)	(120,234)	0	0	0	0	0	(119,988)	(119,988)	0	(246)	0	(246)
Ending Balance at Sep. 30, 2011	1,897,474	275,000	899	(15,028)	2,278,753	(73,800)	(629,626)	1,836,198	49,158	(917)	13,035	61,276	1,897,474	(73,800)	13,035	49,158	1,909,998	(917)	1,884,439
Beginning balance at Jun. 30, 2011
Comprehensive Income:
Net income	14,541												14,541
Preferred unit distributions													(5,850)
Ending Balance at Sep. 30, 2011	$ 1,897,474												$ 1,897,474