Consolidated Statements of Changes In Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock	Additional Paid-in Capital	Cumulative Series C Six Point Seven Five Percent Redeemable Perpetual Preferred Stock [Member]	Distributions in Excess of Accumulated Earnings	Non-controlling interests - Common OP Units	Accumulated Other Comprehensive Loss
Beginning Balance at Dec. 31, 2012	$ 924,302	$ 416	$ 1,012,930	$ 136,144	$ (287,652)	$ 65,054	$ (2,590)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock through exercise of options	246	0	246	0	0	0	0
Issuance of common stock through employee stock purchase plan	170	0	170	0	0	0	0
Compensation expenses related to stock options and restricted stock	1,135	0	1,135	0	0	0	0
Adjustment for fair market value of swap	442	0	0	0	0	0	442
Net income available to Common Shares	40,468	0	0	2,311	35,024	3,133	0
Distributions	(25,012)	0	0	(2,311)	(20,837)	(1,864)	0
Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs	(277)	0	(277)	0	0	0	0
Ending Balance at Mar. 31, 2013	$ 941,474	$ 416	$ 1,014,204	$ 136,144	$ (273,465)	$ 66,323	$ (2,148)