Noncontrolling Interests (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Noncontrolling Interests in the Operating Partnership [Roll Forward]
Beginning noncontrolling interests in the Operating Partnership	$ 110,655	$ 120,838
Adjustment of noncontrolling interests in the Operating Partnership to fair value	14,366	13,081
Conversion of Common Units to Common Stock	(63)	(186)
Net income attributable to noncontrolling interests in the Operating Partnership	827	507
Distributions to noncontrolling interests in the Operating Partnership	(1,584)	(1,610)
Total noncontrolling interests in the Operating Partnership	124,201	132,630
Net Income Available for Common Stockholders and Transfers From Noncontrolling Interests in the Operating Partnership [Abstract]
Net income available for common stockholders	16,694	10,136
Increase in additional paid in capital from conversion of Common Units to Common Stock	63	186
Change from net income available for common stockholders and transfers from noncontrolling interests	$ 16,757	$ 10,322
Noncontrolling Interests in Consolidated Affiliates [Abstract]
Consolidated joint venture, partner's interest (in hundredths)	50.00%