Stockholders' Equity - Computation of basic and diluted earnings (loss) per common share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2014
Weighted average Common Shares outstanding
Weighted average Common Shares outstanding	105,306,479	100,384,606	103,970,376	99,928,738
Nonvested shares	(1,318,730)	(1,111,579)	(1,260,457)	(1,109,723)
Weighted average Common Shares—Basic	103,987,749	99,273,027	102,709,919	98,819,015
Dilutive effect of restricted stock	691,064	580,989	646,341	599,042
Dilutive effect of employee stock purchase plan	90,732	91,186	114,274	136,038
Weighted average Common Shares outstanding—Diluted	104,769,545	99,945,202	103,470,534	99,554,095
Net Income (Loss)
Income from continuing operations	$ 12,157	$ 17,586	$ 21,320	$ 22,635
Discontinued operations	(12)	330	(20)	663
NET INCOME	$ 12,145	$ 17,916	$ 21,300	$ 23,298	$ 23,298
Basic Earnings (Loss) Per Common Share
Income from continuing operations (in dollars per share)	$ 0.12	$ 0.18	$ 0.21	$ 0.23
Discontinued operations (in dollars per share)	0.00	0.00	0.00	0.01
Net income (in dollars per share)	0.12	0.18	0.21	0.24
Diluted Earnings (Loss) Per Common Share
Income from continuing operations (in dollars per share)	0.12	0.18	0.21	0.23
Discontinued operations (in dollars per share)	0.00	0.00	0.00	0.00
Net income (in dollars per share)	$ 0.12	$ 0.18	$ 0.21	$ 0.23