Noncontrolling Interests (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Noncontrolling Interests in the Operating Partnership
Beginning noncontrolling interests in the Operating Partnership			$ 120,838	$ 129,769
Adjustments of noncontrolling interests in the Operating Partnership to fair value			(10,177)	(1,480)
Conversion of Common Units to Common Stock			(1,344)	(2,958)
Net income attributable to noncontrolling interests in the Operating Partnership	366	366	1,496	2,819
Distributions to noncontrolling interests in the Operating Partnership			(4,818)	(4,857)
Total noncontrolling interests in the Operating Partnership	105,995	123,293	105,995	123,293
Net Income Available for Common Stockholders and Transfers From Noncontrolling Interests in the Operating Partnership.
Net income available for common stockholders	7,002	6,878	27,250	52,773
Increase in additional paid in capital from conversion of Common Units to Common Stock	709	0	1,344	2,957
Change in equity from net income available for common stockholders and conversion of Common Units to Common Stock	$ 7,711	$ 6,878	$ 28,594	$ 55,730
Consolidated joint venture, partner's interest (in hundredths)	50.00%		50.00%