Stock-based Compensation - Options (Details) - Options - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Mar. 29, 2018
Number of options outstanding [Roll Forward]
Options outstanding, beginning of period (in shares)	2,666,000
Granted (in shares)	0	60,000
Exercised (in shares)	(22,000)
Options outstanding, end of period (in shares)	2,644,000		2,666,000
Options vested and unvested options expected to vest, net of forfeitures, end of period (in shares)	2,616,000
Options exercisable, end of period (in shares)	1,694,000
Weighted average exercise price [Roll Forward]
Options outstanding, beginning of period (in dollars per share)	$ 3.81
Exercised (in dollars per share)	2.94
Options outstanding, end of period (in dollars per share)	3.81		$ 3.81
Options vested and unvested options expected to vest, net of forfeitures (in dollars per share)	3.79
Options exercisable, end of period (in dollars per share)	$ 3.41
Weighted-average grant date fair value of stock options granted (in dollars per share)		$ 2.76
Weighted average Remaining Contractual Life [Abstract]
Options outstanding	6 years 7 months 28 days		6 years 10 months 13 days
Options vested and unvested options expected to vest, net of forfeitures, end of period	6 years 7 months 21 days
Option exercisable, end of period	5 years 9 months 22 days
Aggregate Intrinsic Value [Abstract]
Options outstanding, beginning of period	$ 13,149
Exercised	97
Options outstanding, end of period	9,409		$ 13,149
Options vested and expected to vest, end of period	9,352
Options exercisable, end of period	$ 6,523
Closing price (in dollars per share)				$ 7.25