Summary of Significant Accounting Policies - Earnings Per Share (Details) - USD ($) shares in Thousands, $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator (for basic and diluted earnings per share)
Net income (loss)		$ 38,337	$ 12,522	$ 11,488	$ 4,888	$ (21,531)	$ (24,443)	$ (31,403)	$ (5,100)	$ 67,235	$ (82,477)	$ 10,529
Less income allocated to RSUs										(917)	0	(240)
Numerator for basic and diluted earnings per share										$ 66,318	$ (82,477)	$ 10,289
Denominator
Basic weighted-average shares outstanding		82,401	83,230	83,773	83,965	83,775	84,107	83,903	57,335	83,339	77,373	56,342
Effect of dilutive securities:
Stock options held by employees and directors										300	0	897
Diluted weighted-average shares outstanding		82,684	83,518	84,051	84,225	83,775	84,107	83,903	57,335	83,639	77,373	57,239
Anti-dilutive securities	[1]									0	1,907	0

[1] Amount outstanding at Balance Sheet date, before application of the treasury stock method and not weighted for period outstanding.