Consolidated Statements of Changes In Equity (USD $)	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, 2013	$ 963,205,000	$ 834,000	$ 1,021,365,000	$ 136,144,000	$ (264,083,000)	$ 69,872,000	$ (927,000)
Stock Issued During Period, Value, Conversion of Units	0	(1,000)	(501,000)	0	0	(502,000)	0
Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs	(51,000)	0	(51,000)	0	0	0	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock through employee stock purchase plan	311,000	0	311,000	0	0	0	0
Compensation expenses related to stock options and restricted stock	733,000	0	733,000	0	0	0	0
Adjustment for fair market value of swap	445,000	0	0	0	0	0	445,000
Release Of Common Shares From Escrow	(1,935,000)	(1,000)	(1,934,000)	0	0	0	0
Net income available to Common Shares	43,890,000	0	0	2,310,000	38,099,000	3,481,000	0
Distributions	(31,864,000)	0	0	(2,310,000)	(27,081,000)	(2,473,000)	0
Ending Balance at Mar. 31, 2014	$ 974,734,000	$ 834,000	$ 1,020,925,000	$ 136,144,000	$ (253,065,000)	$ 70,378,000	$ (482,000)