Summary of Significant Accounting Policies - Net Income (Loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator
Net income (loss)	$ 111,724	$ (25,607)	$ (22,838)	$ (33,194)	$ 90,982	$ (29,155)	$ (16,485)	$ (29,436)	$ 30,085	$ 15,906	$ (843)
Denominator for basic net income (loss) per share
Weighted-average common shares outstanding (in shares)									33,113	34,097	36,761
Dilutive effect of stock options and restricted awards (in shares)									993	1,093	0
Weighted-average diluted shares outstanding (in shares)									34,106	35,190	36,761
Basic (in dollars per share)	$ 3.45	$ (0.78)	$ (0.68)	$ (0.98)	$ 2.70	$ (0.86)	$ (0.48)	$ (0.85)	$ 0.91	$ 0.47	$ (0.02)
Diluted (in dollars per share)	$ 3.37	$ (0.78)	$ (0.68)	$ (0.98)	$ 2.63	$ (0.86)	$ (0.48)	$ (0.85)	$ 0.88	$ 0.45	$ (0.02)
Anti-dilutive stock options and restricted stock units (in shares)									1,363	549	4,185