Description of Business and Summary of Significant Accounting Policies - Computation of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, 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
Earnings Per Share [Abstract]
Net income (loss)	$ (184)	$ (7,596)	$ (6,995)	$ 13,880	$ 12,108	$ 7,996	$ 10,474	$ 10,286	$ (895)	$ 40,864	$ 33,883
Weighted average shares outstanding, basic (in shares)									48,807	48,388	48,198
Basic income (loss) per share (in dollars per share)	$ 0.00	$ (0.16)	$ (0.14)	$ 0.29	$ 0.24	$ 0.17	$ 0.22	$ 0.21	$ (0.02)	$ 0.84	$ 0.70
Effect of stock options outstanding:
Weighted average shares outstanding, basic (in shares)									48,807	48,388	48,198
Assumed exercise, at the strike price at the beginning of year (in shares)									0	1,302	1,410
Assumed repurchase of shares under treasury stock method (in shares)									0	(666)	(888)
Diluted weighted average shares (in shares)									48,807	49,024	48,720
Diluted income (loss) per share (in dollars per share)	$ 0.00	$ (0.16)	$ (0.14)	$ 0.28	$ 0.24	$ 0.17	$ 0.21	$ 0.21	$ (0.02)	$ 0.83	$ 0.70