Stockholders' Equity - Service-Based Stock Options (Details) - Service Based Stock Options [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Stock-based compensation
Vesting period	3 years
Contractual term	10 years
Number of Shares
Outstanding at the beginning of the period (in shares)	8,142,831
Granted (in shares)	6,186,260
Exercised (in shares)	(1,219,976)
Forfeited or expired (in shares)	(1,295,444)
Outstanding at the end of the period (in shares)	11,813,671	8,142,831
Exercisable at the end of the period (in shares)	5,133,792
Vested and expected to vest at the end of the period (in shares)	11,813,671
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 5.38
Granted (in dollars per share)	8.32
Exercised (in dollars per share)	4.59
Forfeited or expired (in dollars per share)	8.68
Outstanding at the end of the period (in dollars per share)	6.64	$ 5.38
Exercisable at the end of the period (in dollars per share)	5.52
Vested and expected to vest at the end of the period (in dollars per share)	$ 6.64
Additional option disclosures
Outstanding at the end of the period, weighted average remaining contractual term	7 years 3 months 7 days
Exercisable at the end of the period, weighted average remaining contractual term	4 years 4 months 13 days
Vested and expected to vest at the end of the period, weighted average remaining contractual term	7 years 3 months 7 days
Outstanding at the end of the period, aggregate intrinsic value	$ 15,409
Exercisable at the end of the period, aggregate intrinsic value	12,329
Vested and expected to vest at the end of the period, aggregate intrinsic value	15,409
Total unrecognized compensation cost related to non-vested shares	$ 25,900
Unrecognized compensation cost, weighted-average period	2 years 3 months 18 days
Total fair value of shares vested	$ 1,800
Weighted-average assumption used for grants
Dividend yield	0.00%	0.00%	0.00%
Expected volatility, minimum	76.80%	65.80%	57.30%
Expected volatility, maximum	96.80%	83.90%	61.50%
Risk-free interest rate, minimum	0.58%	0.37%	2.11%
Risk-free interest rate, maximum	1.31%	1.21%	2.53%
Expected life		6 years	6 years
Stock-based compensation
Weighted-average grant date fair values of options granted (in dollars per share)	$ 5.90	$ 1.54	$ 1.28
Exercised during the period, aggregate intrinsic value	$ 10,100	$ 1,800	$ 100
Stock-based compensation expense	$ 9,900	$ 1,700	$ 2,200
Minimum
Weighted-average assumption used for grants
Expected life	5 years 7 months 6 days
Maximum
Weighted-average assumption used for grants
Expected life	5 years 9 months 18 days
Vesting over the first year
Stock-based compensation
Vesting percentage	34.00%
Vesting over the second year
Stock-based compensation
Vesting percentage	33.00%
Vesting over the third year
Stock-based compensation
Vesting percentage	33.00%