Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share
Net income (loss) for basic and diluted income (loss) per share	$ (880)	$ 229	$ (3,035)	$ 4,377	$ (2,418)	$ (46,967)	$ 4,643	$ 5,302	$ 691	$ (39,440)	$ (25,918)
Shares of common stock and common stock equivalents:
Average common shares used in basic computation	33,003	33,002	33,035	32,890	32,855	33,105	33,125	32,949	33,003	33,009	32,906
Effect of dilutive securities (in shares)									1,404
Average common shares used in diluted computation	33,003	34,421	33,035	33,993	32,855	33,105	34,222	34,130	34,407	33,009	32,906
Income (loss) per share:
Basic (in dollars per share)	$ (0.03)	$ 0.01	$ (0.09)	$ 0.13	$ (0.07)	$ (1.42)	$ 0.14	$ 0.16	$ 0.02	$ (1.19)	$ (0.79)
Diluted (in dollars per share)	$ (0.03)	$ 0.01	$ (0.09)	$ 0.13	$ (0.07)	$ (1.42)	$ 0.14	$ 0.16	$ 0.02	$ (1.19)	$ (0.79)
Anti-dilutive equity awards not included in the detailed earnings per share computation
Equity awards not included in the diluted earnings per share computation									1,400	0	0