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	31,143	0	0	0	0	0	28,985	28,985	1,862	121	175	2,158	31,143	0	175	1,862	28,985	121	30,968
Amortization of loss on derivative instruments	(1,756)	0	0	0	0	(1,752)	0	(1,752)	0	(4)	0	(4)	(1,756)	(1,752)	0	0	0	(4)	(1,756)
Change In Fair Value Of Derivative Instruments Net Of Settlement	(25,789)	0	0	0	0	(25,729)	0	(25,729)	0	(60)	0	(60)	(25,789)	(25,729)	0	0	0	(60)	(25,789)
Total comprehensive income	7,110							5,008				2,102	7,110						6,935
Deferred compensation plan, net	(111)	0	0	(314)	203	0	0	(111)	0	0	0	0	111	0	0	0	111	0	111
Restricted stock issued, net of amortization	3,426	0	0	0	3,426	0	0	3,426	0	0	0	0
Common stock redeemed for taxes withheld for stock based compensation, net	(1,404)	0	0	0	(1,404)	0	0	(1,404)	0	0	0	0
Common stock issued for dividend reinvestment plan	1,314	0	1	0	1,313	0	0	1,314	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	128	0	0	0	0	0	0	0	0	0	128	128	128	0	128	0	0	0	0
Distributions to partners	(1,212)	0	0	0	0	0	0	0	0	0	(1,212)	(1,212)	(77,076)	0	(1,212)	0	(75,574)	(290)	(75,864)
Preferred unit distributions													(11,700)	0	0	(1,862)	(9,838)	0	(11,700)
Restricted stock issued by Parent Company, net of amortization													3,426	0	0	0	3,426	0	3,426
Common units issued as a result of common stock issued by Parent Company, net of repurchases													(90)	0	0	0	(90)	0	(90)
Common units exchanged for common stock of Parent Company													0	0	0	0	7,311	(7,311)	0
Cash dividends declared:
Preferred stock/unit	(11,700)	0	0	0	0	0	(9,838)	(9,838)	(1,862)	0	0	(1,862)
Common stock/unit ($.925 per share)	(75,864)	0	0	0	0	0	(75,574)	(75,574)	0	(290)	0	(290)
Ending Balance at Jun. 30, 2010	1,852,293	275,000	819	(16,823)	2,035,729	(73,950)	(428,264)	1,792,511	49,158	(215)	10,839	59,782	1,852,293	(73,950)	10,839	49,158	1,866,461	(215)	1,841,454
Beginning balance at Mar. 31, 2010
Comprehensive Income:
Net income	13,704												13,704
Preferred unit distributions													(5,850)
Ending Balance at Jun. 30, 2010	1,852,293												1,852,293
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	27,067	0	0	0	0	0	24,884	24,884	1,862	50	271	2,183	27,067	0	271	1,862	24,884	50	26,796
Amortization of loss on derivative instruments	(4,733)	0	0	0	0	(4,723)	0	(4,723)	0	(10)	0	(10)	4,733	4,723	0	0	0	10	4,733
Total comprehensive income	31,800							29,607				2,193	31,800						31,529
Deferred compensation plan, net	1,905	0	0	1,190	715	0	0	1,905	0	0	0	0	(1,905)	0	0	0	(1,905)	0	(1,905)
Restricted stock issued, net of amortization	5,391	0	0	0	5,391	0	0	5,391	0	0	0	0
Common stock redeemed for taxes withheld for stock based compensation, net	(1,824)	0	0	0	(1,824)	0	0	(1,824)	0	0	0	0
Common stock issued for dividend reinvestment plan	562	0	0	0	562	0	0	562	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	2,509	0	0	0	0	0	0	0	0	0	2,509	2,509	2,509	0	2,509	0	0	0	0
Distributions to partners	(810)	0	0	0	0	0	0	0	0	0	(810)	(810)	(79,720)	0	(810)	0	(78,750)	(160)	(78,910)
Preferred unit distributions													(11,700)	0	0	(1,862)	(9,838)	0	(11,700)
Restricted stock issued by Parent Company, net of amortization													5,391	0	0	0	5,391	0	5,391
Common units issued as a result of common stock issued by Parent Company, net of repurchases													214,107	0	0	0	214,107	0	214,107
Cash dividends declared:
Preferred stock/unit	(11,700)	0	0	0	0	0	(9,838)	(9,838)	(1,862)	0	0	(1,862)
Common stock/unit ($.925 per share)	(78,910)	0	0	0	0	0	(78,750)	(78,750)	0	(160)	0	(160)
Ending Balance at Jun. 30, 2011	1,908,694	275,000	899	(14,985)	2,259,745	(76,162)	(596,898)	1,847,599	49,158	(862)	12,799	61,095	1,908,694	(76,162)	12,799	49,158	1,923,761	(862)	1,895,895
Beginning balance at Mar. 31, 2011
Comprehensive Income:
Net income	18,937												18,937
Preferred unit distributions													(5,850)
Ending Balance at Jun. 30, 2011	$ 1,908,694												$ 1,908,694