Consolidated Statements of Changes In Equity - USD ($) $ in Thousands	Total	Common Stock	Paid-in Capital	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, 2012	$ 924,302	$ 832	$ 1,012,514	$ 136,144	$ (287,652)	$ 65,054	$ (2,590)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of Common OP Units to Common Stock	0	0	280	0	0	(280)	0
Issuance of Common Stock through exercise of options	248	1	247	0	0	0	0
Issuance of Common Stock through employee stock purchase plan	720	1	719	0	0	0	0
Compensation expenses related to stock options and restricted stock	5,952	0	5,952	0	0	0	0
Repurchase of Common Stock or Common OP Units	(1,121)	0	(1,121)	0	0	0	0
Adjustment for Common OP Unitholders in the Operating Partnership	0	0	6,730	0	0	(6,730)	0
Adjustment for fair market value of swap	(1,663)	0	0	0	0	0	(1,663)
Release of common shares from escrow	(3,412)	0	(3,412)	0	0	0	0
Net income	125,905	0	0	9,280	106,919	9,706	0
Distributions	(100,194)	0	0	(9,280)	(83,350)	(7,564)	0
Issuance of OP units	9,686	0	0	0	0	9,686	0
Other	(544)	0	(544)	0	0	0	0
Balance at Dec. 31, 2013	963,205	834	1,021,365	136,144	(264,083)	69,872	(927)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of Common OP Units to Common Stock	0	4	4,091	0	0	(4,095)	0
Issuance of Common Stock through employee stock purchase plan	1,328	1	1,327	0	0	0	0
Compensation expenses related to stock options and restricted stock	7,568	0	7,568	0	0	0	0
Repurchase of Common Stock or Common OP Units	(1,870)	0	(1,870)	0	0	0	0
Adjustment for Common OP Unitholders in the Operating Partnership	0	0	(727)	0	0	727	0
Adjustment for fair market value of swap	(546)	0	0	0	0	0	(546)
Release of common shares from escrow	(1,934)	(1)	(1,933)	0	0	0	0
Net income	138,468	0	0	9,274	118,731	10,463	0
Distributions	(127,689)	0	0	(9,274)	(108,857)	(9,558)	0
Other	(595)	0	(220)	0	0	(375)	0
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 Common OP Units to Common Stock	0	0	225	0	0	(225)	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	1,083	0	1,083	0	0	0	0
Compensation expenses related to stock options and restricted stock	8,582	0	8,582	0	0	0	0
Repurchase of Common Stock or Common OP Units	(3,201)	0	(3,201)	0	0	0	0
Adjustment for Common OP Unitholders in the Operating Partnership	0	0	(496)	0	0	496	0
Adjustment for fair market value of swap	172	0	0	0	0	0	172
Net income	150,512	0	0	9,226	130,145	11,141	0
Distributions	(146,465)	0	0	(9,226)	(126,416)	(10,823)	0
Other	(491)	3	(468)	0	(26)	0	0
Balance at Dec. 31, 2015	$ 992,691	$ 843	$ 1,039,140	$ 136,144	$ (250,506)	$ 67,623	$ (553)