Stockholders' Equity - Other (Details) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021 USD ($) item $ / shares shares	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) item $ / shares shares	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) $ / shares shares	May 25, 2021 shares
Stockholders' Equity
Shares available for issuance	3,100		3,100
Stock option and restricted stock
Stock-based compensation
Stock-based compensation expense (in dollars) | $	$ 1,700	$ 1,300	$ 4,500	$ 4,000
Restricted Stock
Stock-based compensation
Unrecognized compensation cost related to unvested restricted stock (in dollars) | $	$ 4,800		$ 4,800
Weighted-average periods over which unrecognized compensation cost recognized			1 year 8 months 12 days
Number of shares
Unvested options	0		0
Number of shares
Outstanding at the beginning of the period (in shares)			499
Granted (in shares)			582
Vested (in shares)			(522)
Outstanding at the end of the period (in shares)	559		559		499
Weighted-average grant date fair value
Outstanding at the beginning of the period (in dollars per share) | $ / shares			$ 11.26
Granted (in dollars per share) | $ / shares			11.95
Vested (in dollars per share) | $ / shares			11.30
Outstanding at the end of the period (in dollars per share) | $ / shares	$ 11.95		$ 11.95		$ 11.26
Stock options
Stock-based compensation
Unrecognized compensation cost related to unvested stock options (in dollars) | $	$ 3,700		$ 3,700
Weighted-average periods over which unrecognized compensation cost recognized			2 years 6 months
Estimated forfeitures (as a percent)	1.50%		1.50%
Valuation assumptions
Dividend yield (as a percent)			0.00%
Number of shares
Outstanding at the beginning of the period (in shares)			3,935
Granted (in shares)			600
Exercised (in shares)			(50)
Forfeited (in shares)			(8)
Expired (in shares)			(40)
Outstanding at the end of the period (in shares)	4,437		4,437		3,935
Vested at the end of the period (in shares)	3,412		3,412
Exercisable at the end of the period (in shares)	3,412		3,412
Weighted-average exercise price
Outstanding at the beginning of the period (in dollars per share) | $ / shares			$ 11.69
Granted (in dollars per share) | $ / shares			12.02
Exercised (in dollars per share) | $ / shares			10.20
Forfeited (in dollars per share) | $ / shares			14.00
Expired (in dollars per share) | $ / shares			14.78
Outstanding at the end of the period (in dollars per share) | $ / shares	$ 11.67		11.67		$ 11.69
Vested at the end of the period (in dollars per share) | $ / shares	11.60		11.60
Exercisable at the end of the period (in dollars per share) | $ / shares	$ 11.60		$ 11.60
Weighted-average remaining contractual term
Outstanding			5 years		5 years 1 month 6 days
Granted			6 years
Vested at the end of the period			3 years 10 months 24 days
Exercisable at the end of the period			3 years 10 months 24 days
Aggregate intrinsic value
Outstanding at the beginning of the period (in dollars) | $			$ 291
Outstanding at the end of the period (in dollars) | $	$ 3,411		3,411		$ 291
Vested at the end of the period (in dollars) | $	3,047		3,047
Exercisable at the end of the period (in dollars) | $	$ 3,047		$ 3,047
Weighted-average grant date fair value of options granted (in dollars per share) | $ / shares			$ 4.72
Weighted average grant date fair value of options granted | $ / shares			$ 4.72
Number of options granted			600
Performance-based Stock Option
Number of shares
Unvested options	500		500
Performance-based Restricted Stock
Aggregate intrinsic value
Vesting period			3 years
Time Based Restricted Stock Awards and Stock Option
Stockholders' Equity
Number of equal annual installments for vesting of awards | item	3		3
Time Based Restricted Stock Awards and Stock Option | Black Scholes Pricing Model
Valuation assumptions
Weighted-average expected term (years)			6 years		6 years
Time Based Restricted Stock Awards and Stock Option | Minimum | Black Scholes Pricing Model
Valuation assumptions
Risk-free interest rate (as a percent)			0.94%		0.42%
Volatility (as a percent)			37.30%		44.20%
Time Based Restricted Stock Awards and Stock Option | Maximum | Black Scholes Pricing Model
Valuation assumptions
Risk-free interest rate (as a percent)			1.08%		0.50%
Volatility (as a percent)			40.60%		46.10%
Time-based Restricted Stock
Aggregate intrinsic value
Vesting period			3 years
Common Class A
Stockholders' Equity
Shares authorized for issuance						10,200