Stock-Based Compensation - Stock Options Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Outstanding stock options
Number of Shares
Outstanding at beginning of period (in shares)	3,374,541
Granted (in shares)	0
Exercised (in shares)	0
Forfeited (in shares)	(194,936)
Outstanding at end of period (in shares)	3,179,605		3,374,541
Options vested or expected to vest at end of period (in shares)	3,179,605
Options exercisable at end of period (in shares)	1,617,860
Weighted Average Exercise Price
Outstanding at beginning of period (in dollars per share)	$ 6.53
Granted (in dollars per share)	0.00
Exercised (in dollars per share)	0.00
Forfeited (in dollars per share)	6.94
Outstanding at end of period (in dollars per share)	6.51		$ 6.53
Options vested or expected to vest at end of period (in dollars per share)	6.51
Options exercisable at end of period (in dollars per share)	$ 6.46
Weighted Average Contractual Term
Outstanding	7 years 8 months 27 days		7 years 7 months 2 days
Options vested or expected to vest at end of period	7 years 8 months 27 days
Options exercisable at end of period	7 years 1 month 13 days
Aggregate Intrinsic Value
Outstanding	$ 93		$ 0
Options vested or expected to vest at end of period	93
Options exercisable at end of period	$ 9
Weighted average grant-date fair value per share of stock options granted (in dollars per share)		$ 4.82
Aggregate intrinsic value of stock options exercised		$ 100
Non Employee Stock Options
Number of Shares
Granted (in shares)	0	0