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	(4,000)	(3,185,000)	0	0	(3,189,000)	0
Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs	(99,000)	0	(99,000)	0	0	0	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock through employee stock purchase plan	529,000	0	529,000	0	0	0	0
Compensation expenses related to stock options and restricted stock	2,431,000	0	2,431,000	0	0	0	0
Stock Repurchased During Period, Value	(32,000)	0	(32,000)	0	0	0	0
Adjustment for fair market value of swap	927,000	0	0	0	0	0	927,000
Release Of Common Shares From Escrow	(1,934,000)	(1,000)	(1,933,000)	0	0	0	0
Adjustment For Common Unitholders In Operating Partnership	0	0	(50,000)	0	0	50,000	0
Net income available to Common Shares	73,930,000	0	0	4,638,000	63,582,000	5,710,000	0
Distributions	(63,811,000)	0	0	(4,638,000)	(54,315,000)	(4,858,000)	0
Ending Balance at Jun. 30, 2014	$ 975,146,000	$ 837,000	$ 1,025,396,000	$ 136,144,000	$ (254,816,000)	$ 67,585,000	$ 0