Stockholders' Equity and Employee Stock Option Plans Stock option outstanding by exercise price range (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Mar. 31, 2013
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options and SARS Outstanding, Weighted Average Remaining Contractual Term	7 years 7 months 21 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	$ 80
Options and SARS, Outstanding, Weighted Average Exercise Price	$ 11.28	$ 13.94	$ 24.72
Options and SARS, Outstanding, Number	425,722	505,872	285,536	550,540
Options, Vested and Expected to Vest, Outstanding, Number	418,607
Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term	7 years 7 months 21 days
Options, Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price	$ 11.35
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value	$ 78
Options, Exercisable, Number	345,103
Options, Exercisable, Weighted Average Remaining Contractual Term	7 years 5 months 5 days
Options, Exercisable, Weighted Average Exercise Price	$ 12.41
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value	$ 57
$4.51
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 4.51
Exercise Price Range, Number of Outstanding Options and SARS	20,000
Options and SARS Outstanding, Weighted Average Remaining Contractual Term	8 years 4 months 17 days
Exercise Price Range, Outstanding Options, Weighted Average Exercise Price	$ 4.51
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	$ 21
5.22
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 5.22
Exercise Price Range, Number of Outstanding Options and SARS	182,000
Options and SARS Outstanding, Weighted Average Remaining Contractual Term	8 years 8 months 27 days
Exercise Price Range, Outstanding Options, Weighted Average Exercise Price	$ 5.22
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	$ 58
5.45 - 9.10
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 5.45
Exercise Price Range, Upper Range Limit	$ 9.10
Exercise Price Range, Number of Outstanding Options and SARS	31,500
Options and SARS Outstanding, Weighted Average Remaining Contractual Term	8 years 9 months 22 days
Exercise Price Range, Outstanding Options, Weighted Average Exercise Price	$ 7.01
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	$ 1
9.11
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 9.11
Exercise Price Range, Number of Outstanding Options and SARS	73,000
Options and SARS Outstanding, Weighted Average Remaining Contractual Term	7 years 5 months 12 days
Exercise Price Range, Outstanding Options, Weighted Average Exercise Price	$ 9.11
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	$ 0
9.15 - 23.70
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 9.15
Exercise Price Range, Upper Range Limit	$ 23.70
Exercise Price Range, Number of Outstanding Options and SARS	81,590
Options and SARS Outstanding, Weighted Average Remaining Contractual Term	6 years 11 days
Exercise Price Range, Outstanding Options, Weighted Average Exercise Price	$ 21.29
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	$ 0
$24.20 - $32.50
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 24.20
Exercise Price Range, Upper Range Limit	$ 32.5
Exercise Price Range, Number of Outstanding Options and SARS	37,632
Options and SARS Outstanding, Weighted Average Remaining Contractual Term	4 years 9 months 7 days
Exercise Price Range, Outstanding Options, Weighted Average Exercise Price	$ 30.24
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	$ 0