Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Class A common stock	Class B common stock	Class U common stock	Common Stock Class A common stock	Common Stock Class B common stock	Common Stock Class U common stock	Treasury Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Balance, Beginning at Dec. 31, 2020	$ 275,980				$ 6	$ 2	$ 1		$ 828,813	$ (551,786)	$ (1,056)
Balance, Beginning, Shares at Dec. 31, 2020					60,759,405	14,927,613	9,352,729
Issuance of common stock upon exercise of stock options or awards of restricted stock units	(9)								(9)
Issuance of common stock upon exercise of stock options or awards of restricted stock units, Shares					6,045
Stock-based compensation expense	1,071								1,071
Dividends paid	(2,126)								(2,126)
Change in fair value of marketable securities	(69)										(69)
Foreign currency translation gain (loss)	407										407
Net income (loss) attributable to common stockholders	5,429									5,429
Balance, Ending at Mar. 31, 2021	280,683				$ 6	$ 2	$ 1		827,749	(546,357)	(718)
Balance, Ending, Shares at Mar. 31, 2021					60,765,450	14,927,613	9,352,729
Balance, Beginning at Dec. 31, 2021	256,926				$ 6	$ 2	$ 1		780,388	(522,494)	(977)
Balance, Beginning, Shares at Dec. 31, 2021		63,116,896	14,127,613	9,352,729	63,116,896	14,127,613	9,352,729
Issuance of common stock upon exercise of stock options or awards of restricted stock units	218								218
Issuance of common stock upon exercise of stock options or awards of restricted stock units, Shares					66,000
Tax payments related to shares withheld for share-based compensation plans	(257)								(257)
Tax payments related to shares withheld for share-based compensation plans, shares					14,955
Stock-based compensation expense	2,573								2,573
Repurchase of Class A common stock	(7,142)	$ (7,100)							(7,142)
Repurchase of Class A common stock, shares		(1,100,000)			(1,114,470)			1,114,470
Retirement of treasury stock, shares								(1,114,470)
Dividends paid	(2,167)								(2,167)
Change in fair value of marketable securities	(283)										(283)
Net income (loss) attributable to common stockholders	1,887									1,887
Balance, Ending at Mar. 31, 2022	$ 251,755				$ 6	$ 2	$ 1		$ 773,613	$ (520,607)	$ (1,260)
Balance, Ending, Shares at Mar. 31, 2022		62,083,381	14,127,613	9,352,729	62,083,381	14,127,613	9,352,729