Condensed Consolidated Statement of Equity (USD $) In Thousands, except Share data	Total	Preferred Operating Partnership	Operating Partnership	Other Noncontrolling Interests	Common Stock	Paid-in Capital	Accumulated Other Comprehensive Deficit	Accumulated Deficit	Comprehensive Income
Balances at Dec. 31, 2010	$ 939,071	$ 29,733	$ 26,803	$ 1,134	$ 876	$ 1,148,820	$ (5,787)	$ (262,508)
Balances (in shares) at Dec. 31, 2010	87,587,322				87,587,322
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon the exercise of options	10,505				8	10,497
Issuance of common stock upon the exercise of options (in shares)					816,806
Restricted stock grants issued	2				2
Restricted stock grants issued (in shares)					220,630
Restricted stock grants cancelled (in shares)					(10,519)
Issuance of common stock, net of offering costs	112,532				53	112,479
Issuance of common stock, net of offering costs (in shares)					5,335,423
Compensation expense related to stock-based awards	2,711					2,711
Redemption of Operating Partnership units for common stock			(2,344)		3	2,341
Redemption of Operating Partnership units for common stock (in shares)					293,641
Redemption of Operating Partnership units for cash	(271)		(271)
Comprehensive income:
Net income (loss)	22,657	3,084	670	(7)				18,910	22,657
Change in fair value of interest rate swap	(674)	(7)	(18)				(649)		(674)
Total comprehensive income	21,983								21,983
Tax effect from vesting of restricted stock grants and stock option exercises	2,091					2,091
Distributions to Operating Partnership units held by noncontrolling interests	(4,092)	(3,152)	(940)
Distributions to other noncontrolling interests	(13)			(13)
Dividends paid on common stock at $0.28 per share	(25,575)							(25,575)
Balances at Jun. 30, 2011	$ 1,058,944	$ 29,658	$ 23,900	$ 1,114	$ 942	$ 1,278,939	$ (6,436)	$ (269,173)
Balances (in shares) at Jun. 30, 2011	94,243,303				94,243,303