Stock-Based Compensation - Options (Details) - Options - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Number of Options Outstanding [Roll Forward]
Options outstanding, beginning of period (in shares)			2,654,000
Granted (in shares)	0	0	0	0
Exercised (in shares)			(113,000)
Canceled and expired (in shares)			(18,000)
Options outstanding, end of period (in shares)	2,523,000		2,523,000		2,654,000
Options vested and unvested options expected to vest, net of forfeitures, end of period (in shares)	2,510,000		2,510,000
Options exercisable, end of period (in shares)	2,019,000		2,019,000
Weighted-average Exercise Price [Roll Forward]
Options outstanding, beginning of period (in dollars per share)			$ 4.09
Exercised (in dollars per share)			2.37
Canceled and expired (in dollars per share)			4.47
Options outstanding, end of period (in dollars per share)	$ 4.16		4.16		$ 4.09
Options vested and unvested options expected to vest, net of forfeitures (in dollars per share)	4.15		4.15
Options exercisable, end of period (in dollars per share)	$ 3.72		$ 3.72
Weighted average Remaining Contractual Life [Abstract]
Options outstanding			5 years 6 months 11 days		6 years 3 months 11 days
Options vested and unvested options expected to vest, net of forfeitures, end of period			5 years 6 months 7 days
Option exercisable, end of period			4 years 10 months 17 days
Aggregate Intrinsic Value [Abstract]
Options outstanding, beginning of period			$ 2,720
Options outstanding, end of period	$ 1,497		1,497		$ 2,720
Options vested and expected to vest, end of period	1,497		1,497
Options exercisable, end of period	$ 1,451		$ 1,451
Closing price (in dollars per share)	$ 3.56		$ 3.56