Stockholders' Equity - Computation of basic and diluted earnings (loss) per common share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Weighted average Common Shares outstanding
Weighted average Common Shares outstanding	120,895,835	115,463,220	117,981,159	107,829,287
Nonvested shares	(1,797,686)	(1,311,074)	(1,800,180)	(1,277,453)
Weighted average Common Shares—Basic	119,098,149	114,152,146	116,180,979	106,551,834
Dilutive effect of nonvested share-based awards		788,265		697,219
Dilutive effect of employee stock purchase plan	83,242	111,625	96,260	116,794
Weighted average Common Shares outstanding—Diluted	119,181,391	115,052,036	116,277,239	107,365,847
Net Income
Income from continuing operations	$ 3,165	$ 11,857	$ 60,247	$ 33,177
Dividends paid on nonvested share-based awards	(538)		(1,609)
Income from continuing operations applicable to common stockholders	2,627	11,857	58,638	33,177
Discontinued operations	8	(23)	(4)	(43)
NET INCOME	$ 2,635	$ 11,834	$ 58,634	$ 33,134
Basic Earnings (Loss) Per Common Share
Income from continuing operations (in dollars per share)	$ 0.02	$ 0.10	$ 0.50	$ 0.31
Discontinued operations (in dollars per share)	0.00	0.00	0.00	0.00
Net income (in dollars per share)	0.02	0.10	0.50	0.31
Diluted Earnings (Loss) Per Common Share
Income from continuing operations (in dollars per share)	0.02	0.10	0.50	0.31
Discontinued operations (in dollars per share)	0.00	0.00	0.00	0.00
Net income (in dollars per share)	$ 0.02	$ 0.10	$ 0.50	$ 0.31