Stockholders' Equity - Stock Options Outstanding Rollforward (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of Options
Outstanding at December 31 (in shares)	686	1,177	1,205
Granted (in shares)	682	75	120
Exercised (in shares)	(134)	(269)	(10)
Expired, canceled or forfeited (in shares)	(170)	(297)	(138)
Outstanding at December 31 (in shares)	1,064	686	1,177
Exercisable at December 31 (in shares)	307	379	687
Weighted Average Exercise Price
Outstanding at December 31 (in dollars per share)	$ 11.41	$ 11.60	$ 11.65
Granted (in dollars per share)	8.65	8.90	12.04
Exercised (in dollars per share)	9.24	9.06	8.64
Expired, canceled or forfeited (in dollars per share)	10.46	13.68	12.59
Outstanding at December 31 (in dollars per share)	10.06	11.41	11.60
Exercisable at December 31 (in dollars per share)	12.37	11.39	11.60
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price	$ 10.06	$ 11.42	$ 11.58
Stock options, Outstanding, Weighted Average Remaining Contractual Life	3 years 3 months 7 days	2 years 2 months 23 days	2 years 14 days
Stock options, Exercisable, Weighted Average Remaining Contractual Life	1 year 4 months 13 days	1 year 6 months	2 years
Stock options, Outstanding, Aggregate Intrinsic Value	$ 1,268	$ 681	$ 123
Stock options, Exercisable, Aggregate Intrinsic Value	$ 9	$ 382	$ 122
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number	1,064	674	1,154
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term	3 years 3 months 7 days	2 years 14 days	1 year 3 months
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value	$ 1,268	$ 662	$ 111