Consolidated Statements of Changes In Equity - 6 months ended Jun. 30, 2015 - USD ($) $ in Thousands	Total	Common Stock	Paid-in Capital	Cumulative Series Eight Point Zero Three Four Percent Redeemable Perpetual Preferred Stock [Member]	6.75% Series C Cumulative Redeemable Perpetual Preferred Stock	Distributions in Excess of Accumulated Earnings	Non- controlling interests – Common OP Units	Accumulated Other Comprehensive Loss
Balance at Dec. 31, 2014	$ 979,027	$ 838	$ 1,029,601		$ 136,144	$ (254,209)	$ 67,034	$ (381)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of OP Units to common stock	0	0	95		0	0	(95)	0
Issuance of common stock through exercise of options	3,816	2	3,814		0	0	0	0
Issuance of common stock through employee stock purchase plan	509	0	509		0	0	0	0
Compensation expenses related to restricted stock	3,960	0	3,960		0	0	0	0
Stock Repurchased During Period, Value		0	(73)	$ 0	0	0	0	(73)
Adjustment for Common OP Unitholders in the Operating Partnership	0	0	(316)		0	0	316	0
Adjustment for fair market value of swap	(653)	0	0		0	0	0	(653)
Net income	68,639	0	0		4,613	58,972	5,054	0
Distributions	(73,223)	0	0		(4,613)	(63,194)	(5,416)	0
Adjustments to Additional Paid in Capital, Other		(3)				26
Other	(323)		(300)		0		0	0
Balance at Jun. 30, 2015	$ 981,679	$ 843	$ 1,037,290		$ 136,144	$ (258,457)	$ 66,893	$ (1,034)