Condensed Consolidated Statements of Changes in Stockholders' Equity Statement - USD ($)	Total	Common Stock Common Stock, Class A	Common Stock Common Stock, Class B	Additional Paid-In Capital	Treasury Stock, at cost	Retained Earnings	Accumulated Other Comprehensive Loss
At beginning of period at Dec. 31, 2020		$ 275,000	$ 132,000	$ 545,717,000	$ (9,158,000)	$ 1,042,676,000	$ (230,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion Class B to Class A common stock		0	0
Stock-based compensation expense	$ 3,443,000	1,000		3,442,000
Stock option exercises		1,000		3,141,000
Payment consideration to tax authority on employees' behalf				(2,489,000)
Net income	32,328,000					32,328,000
Dividends						(15,396,000)
Translation adjustments, net of tax	(12,000)						(12,000)
At end of period at Mar. 31, 2021	1,600,428,000	277,000	132,000	549,811,000	(9,158,000)	1,059,608,000	(242,000)
At beginning of period at Dec. 31, 2021	1,675,420,000	279,000	132,000	566,573,000	(9,158,000)	1,117,867,000	(273,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion Class B to Class A common stock		116,000	(116,000)
Stock-based compensation expense	3,918,000	1,000		3,917,000
Stock option exercises		0		4,010,000
Payment consideration to tax authority on employees' behalf				(3,629,000)
Net income	31,341,000					31,341,000
Dividends						(16,751,000)
Translation adjustments, net of tax	(12,000)						(12,000)
At end of period at Mar. 31, 2022	$ 1,694,297,000	$ 396,000	$ 16,000	$ 570,871,000	$ (9,158,000)	$ 1,132,457,000	$ (285,000)