Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Accounts receivable, allowance for doubtful accounts	$ 915	$ 919
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	50,000,000	50,000,000
Preferred stock, shares issued	0	0
Common Class A
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	25,992,774	25,457,709
Treasury stock, shares	6,001,151	5,710,416
Common Class B
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized	33,000,000	33,000,000
Common stock, shares issued	19,720,381	19,720,381