Summary of Significant Accounting Policies - Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerator:
Basic net income (loss)	$ 647	$ 117,361	$ 3,086	$ 118,152
Effect of diluted securities		1,200		2,400
Diluted net income (loss)	$ 647	$ 118,561	$ 3,086	$ 120,552
Denominator:
Basic weighted average shares outstanding (in shares)	22,487	22,403	22,479	22,396
Effect of diluted securities (in shares)	313	4,245	306	4,219
Diluted weighted average shares outstanding (in shares)	22,800	26,648	22,785	26,615
Basic earnings per share (in dollars per share)	$ 0.03	$ 5.24	$ 0.14	$ 5.28
Diluted earnings per share (in dollars per share)	$ 0.03	$ 4.45	$ 0.14	$ 4.53