Stockholders' Equity - Summary of the share activity under the 2015 Plan (Details) - 2015 Equity Incentive Plan - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Number of shares
Outstanding at the beginning	4,560
Granted	593
Exercised	(308)
Forfeited	(83)
Expired	(407)
Outstanding at the end	4,355	4,560
Expected to vest	4,355
Exercisable	3,274
Weighted Average Exercise Price
Outstanding at the beginning (in dollars per share)	$ 6.29
Granted (in dollars per share)	4.33
Exercised (in dollars per share)	1.02
Forfeited (in dollars per share)	6.48
Expired (in dollars per share)	7.38
Outstanding at the end (in dollars per share)	6.29	$ 6.29
Expected to vest (in dollars per share)	6.29
Exercisable (in dollars per share)	$ 6.18
Weighted Average Remaining Contractual Term
Weighted Average Remaining Term (in years)	4 years 10 days	3 years 25 days
Vested and expected to vest (in years)	4 years 10 days
Exercisable (in years)	2 years 4 months 17 days
Aggregate Intrinsic Value
Outstanding	$ 1,766	$ 2,670
Expected to vest	1,766
Exercisable	$ 1,261