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
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Weighted average Common Shares outstanding
Weighted average Common Shares outstanding	116,528,181	105,306,479	116,499,667	103,970,376
Nonvested shares	(1,807,082)	(1,318,730)	(1,801,448)	(1,260,457)
Weighted average Common Shares—Basic	114,721,099	103,987,749	114,698,219	102,709,919
Dilutive effect of restricted stock	861,037	691,064	796,283	646,341
Dilutive effect of employee stock purchase plan	92,228	90,732	102,327	114,274
Weighted average Common Shares outstanding—Diluted	115,674,364	104,769,545	115,596,829	103,470,534
Net Income
Income from continuing operations	$ 25,224	$ 12,157	$ 57,082	$ 21,320
Discontinued operations	0	(12)	(12)	(20)
NET INCOME	$ 25,224	$ 12,145	$ 57,070	$ 21,300
Basic Earnings (Loss) Per Common Share
Income from continuing operations (in dollars per share)	$ 0.22	$ 0.12	$ 0.50	$ 0.21
Discontinued operations (in dollars per share)	0.00	0.00	0.00	0.00
Net income (in dollars per share)	0.22	0.12	0.50	0.21
Diluted Earnings (Loss) Per Common Share
Income from continuing operations (in dollars per share)	0.22	0.12	0.49	0.21
Discontinued operations (in dollars per share)	0.00	0.00	0.00	0.00
Net income (in dollars per share)	$ 0.22	$ 0.12	$ 0.49	$ 0.21