Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2016		53,667,631
Beginning balance at Dec. 31, 2016	$ 863,068	$ 537	$ 1,182,245	$ (319,714)
Increase (Decrease) in Stockholders' Equity
Common shares issued under share-based compensation plans, net of shares withheld for employee taxes (in shares)		49,657
Common shares issued under share-based compensation plans, net of shares withheld for employee taxes	50	$ 1	49
Repurchased of common stock (in shares)		(357,848)
Repurchases of common stock	(5,008)	$ (4)	(5,004)
Dividends on common stock	(15,940)			(15,940)
Share-based compensation	2,466		2,466
Net loss	(105,064)			(105,064)
Ending balance (in shares) at Jun. 30, 2017		53,359,440
Ending balance at Jun. 30, 2017	$ 739,572	$ 534	1,179,756	(440,718)
Beginning balance (in shares) at Dec. 31, 2017	53,447,950	53,447,950
Beginning balance at Dec. 31, 2017	$ 644,602	$ 534	1,181,327	(537,259)
Increase (Decrease) in Stockholders' Equity
Common shares issued under share-based compensation plans, net of shares withheld for employee taxes (in shares)		136,689
Common shares issued under share-based compensation plans, net of shares withheld for employee taxes	108	$ 2	106
Repurchased of common stock (in shares)		(22,836)
Repurchases of common stock	(240)	$ 0	(240)
Dividends on common stock	(16,213)			(16,213)
Share-based compensation	680		680
Net loss	$ (48,686)			(48,686)
Ending balance (in shares) at Jun. 30, 2018	53,561,803	53,561,803
Ending balance at Jun. 30, 2018	$ 580,251	$ 536	$ 1,181,873	$ (602,158)