Consolidated Statement of Changes in Shareholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common stock	Additional Paid-in Capital	(Accumulated deficit) retained earnings	Accumulated other comprehensive loss	Treasury Stock
Common shares outstanding (in shares) at Dec. 31, 2014		195,743,154				0
Stockholders' Equity (Deficit) at Dec. 31, 2014	$ (87,297)	$ 1,957	$ 57,683	$ (146,937)	$ 0	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive loss	(31)				(31)
Exercise of stock options (in shares)		396,010
Exercise of stock options	2,251	$ 5	2,246
Income tax benefit from exercise of stock options	1,536		1,536
Issuance of restricted stock (in shares)		46,750
Issuance of restricted stock	935		935
Issuance of common stock (in shares)		30,682
Issuance of common stock	614		614
Stock-based compensation expense	1,885		1,885
Net income	89,388			89,388
Common shares outstanding (in shares) at Dec. 31, 2015		196,216,596				0
Stockholders' Equity (Deficit) at Dec. 31, 2015	9,281	$ 1,962	64,899	(57,549)	(31)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive loss	292				292
Exercise of stock options (in shares)		275,543
Exercise of stock options	1,915	$ 3	1,912
Issuance of restricted stock (in shares)		31,871
Issuance of restricted stock	814		814
Stock-based compensation expense	3,795		3,795
Net income	$ 130,241			130,241
Common shares outstanding (in shares) at Dec. 31, 2016	196,524,010	196,524,010				0
Stockholders' Equity (Deficit) at Dec. 31, 2016	$ 146,338	$ 1,965	71,420	72,692	261	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive loss	$ (435)				(435)
Exercise of stock options (in shares)	1,055,624	1,055,624
Exercise of stock options	$ 6,021	$ 11	6,010
Issuance of restricted stock (in shares)		35,430
Issuance of restricted stock	815		815
Repurchases of common stock (in shares)						2,092,774
Repurchases of common stock	(50,000)					$ (50,000)
Stock-based compensation expense	2,868		2,868
Net income	$ 193,529			193,529
Common shares outstanding (in shares) at Dec. 31, 2017	195,522,290	197,615,064.000				2,092,774
Stockholders' Equity (Deficit) at Dec. 31, 2017	$ 299,136	$ 1,976	$ 81,113	$ 266,221	$ (174)	$ (50,000)