Stock-Based Compensation - Option Activity (Details) - Employee Stock Option - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Shares
Outstanding, beginning balance (in shares)	3,030
Number of shares, options exercised (in shares)	(275)
Expired and/or forfeited (in shares)	(808)
Outstanding, ending balance (in shares)	1,947
Options exercisable (in shares)	1,843
Weighted-Average Exercise Price
Outstanding, weighted average exercise, beginning balance (in dollars per share)	$ 2.09
Weighted-average exercise price, options exercised (in dollars per share)	1.18
Expired and/or forfeited, weighted average exercise price (in dollars per share)	2.02
Outstanding, weighted average exercise, ending balance (in dollars per share)	2.25
Options exercisable, weighted average option price per share (in dollars per share)	$ 2.31
Outstanding, weighted average remaining contractual life (years)	6 years 2 months 8 days
Options exercisable, weighted average remaining contractual life (years)	6 years 1 month 6 days
Outstanding, intrinsic value	$ 283	$ 1,372
Options exercisable, intrinsic value	$ 245