Stock Plans - Stock Options (Details) - USD ($) $ / shares in Units, shares in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Number of Options
Options outstanding at the beginning of the period (in shares)	4,423
Options granted (in shares)	2,209
Options exercised (in shares)	0
Options cancelled (in shares)	(1,917)
Options outstanding at the end of the period (in shares)	4,715	4,423
Vested and exercisable (in shares)	1,404
Weighted-Average Exercise Price
Balance at the beginning of the period (in dollars per share)	$ 9.60
Options granted (in dollars per share)	3.01
Options exercised (in dollars per share)	0
Options cancelled (in dollars per share)	9.55
Balance at the end of the period (in dollars per share)	6.53	$ 9.60
Vested and exercisable (in dollars per share)	$ 12.86
Weighted-Average Remaining Contractual Term (Years)
Outstanding	5 years 1 month 9 days
Vested and exercisable	3 years 4 months 9 days
Aggregate Intrinsic Value
Outstanding	$ 6,000
Vested and exercisable	0
Additional disclosures related to stock options
Total intrinsic value for stock options exercised	0	$ 0
Total intrinsic value for stock options exercisable	$ 0	$ 2,000