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
Net (loss) income for basic and diluted (loss) income per share	$ 5,716	$ (23,911)	$ (5,217)	$ (2,506)	$ 82,337	$ 2,710	$ (10,210)	$ 16,733	$ (25,918)	$ 91,570	$ 50,892
Shares of common stock and common stock equivalents:
Average common shares used in basic computation	32,607	32,725	33,189	33,106	33,433	33,859	34,076	34,268	32,906	33,907	35,349
Effect of dilutive securities (in shares)										908	1,016
Average common shares used in diluted computation	33,988	32,725	33,189	33,106	34,359	34,547	34,076	34,451	32,906	34,815	36,365
(Loss) income per share:
Basic (in dollars per share)	$ 0.18	$ (0.73)	$ (0.16)	$ (0.08)	$ 2.46	$ 0.08	$ (0.30)	$ 0.49	$ (0.79)	$ 2.70	$ 1.44
Diluted (in dollars per share)	$ 0.17	$ (0.73)	$ (0.16)	$ (0.08)	$ 2.40	$ 0.08	$ (0.30)	$ 0.47	$ (0.79)	$ 2.63	$ 1.40
Anti-dilutive equity awards not included in the detailed earnings per share computation
Equity awards not included in the diluted earnings per share computation									0	100