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, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Weighted average Common Shares outstanding
Weighted average Common Shares outstanding	100,440,463	97,651,673	100,101,187	96,677,774
Nonvested shares	(1,103,379)	(1,793,639)	(1,107,585)	(1,832,242)
Weighted average Common Shares—Basic	99,337,084	95,858,034	98,993,602	94,845,532
Dilutive effect of restricted stock	595,930	1,369,047	597,713	1,346,032
Dilutive effect of employee stock purchase plan	63,541	101,963	102,355	118,854
Weighted average Common Shares outstanding—Diluted	99,996,555	97,329,044	99,693,670	96,310,418
Net Income (Loss)
Income from continuing operations	$ 16,848	$ 8,437	$ 39,482	$ 24,920
Noncontrolling interests’ share in net income		(162)		(313)
Income from continuing operations attributable to common stockholders	16,848	8,275	39,482	24,607
Discontinued operations	10,632	(4,284)	11,296	(10,793)
NET INCOME ATTRIBUTABLE TO COMMON STOCKHOLDERS	$ 27,480	$ 3,991	$ 50,778	$ 13,814
Basic Earnings (Loss) Per Common Share
Income from continuing operations (in dollars per share)	$ 0.17	$ 0.09	$ 0.40	$ 0.26
Discontinued operations (in dollars per share)	0.11	(0.05)	0.11	(0.11)
Net income attributable to common stockholders (in dollars per share)	0.28	0.04	0.51	0.15
Diluted Earnings (Loss) Per Common Share
Income from continuing operations (in dollars per share)	0.17	0.09	0.40	0.26
Discontinued operations (in dollars per share)	0.10	(0.05)	0.11	(0.12)
Net income attributable to common stockholders (in dollars per share)	$ 0.27	$ 0.04	$ 0.51	$ 0.14