Stock-Based Compensation - Options (Details) - USD ($) $ / shares in Units, shares in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Aggregate Intrinsic Value [Abstract]
Closing price (in dollars per share)	$ 8.33		$ 8.33
Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation costs related to unvested stock options not yet recognized	$ 500,000		$ 500,000
Value of estimated forfeitures			$ 90,000
Weighted-average period of amortization			1 year 9 months 18 days
Number of Options Outstanding [Roll Forward]
Options outstanding, beginning of period (in shares)			1,885
Granted (in shares)	0	0	0	0
Exercised (in shares)			(482)
Options outstanding, end of period (in shares)	1,403		1,403		1,885
Options vested and unvested options expected to vest, net of forfeitures, end of period (in shares)	1,397		1,397
Options exercisable, end of period (in shares)	1,081		1,081
Weighted-average Exercise Price [Roll Forward]
Options outstanding, beginning of period (in dollars per share)			$ 4.42
Exercised (in dollars per share)			3.30
Options outstanding, end of period (in dollars per share)	$ 4.80		4.80		$ 4.42
Options vested and unvested options expected to vest, net of forfeitures (in dollars per share)	4.81		4.81
Options exercisable, end of period (in dollars per share)	$ 5.13		$ 5.13
Weighted average Remaining Contractual Life [Abstract]
Options outstanding			5 years 9 months 10 days		6 years 2 months 1 day
Options vested and unvested options expected to vest, net of forfeitures, end of period			5 years 9 months 7 days
Option exercisable, end of period			5 years 1 month 28 days
Aggregate Intrinsic Value [Abstract]
Options outstanding, beginning of period			$ 9,713,000
Options outstanding, end of period	$ 5,094,000		5,094,000		$ 9,713,000
Options vested and expected to vest, end of period	5,064,000		5,064,000
Options exercisable, end of period	$ 3,605,000		$ 3,605,000