Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Common Stock [Member] Class A [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Loss [Member]	Retained Earnings [Member]	Total
Balance at beginning of period at Dec. 31, 2019	$ 91	$ 557,544	$ (1,324,826)	$ (85,292)	$ 1,727,772	$ 875,289
Stockholders' Equity [Roll Forward]
Net income	0	0	0	0	19,730	19,730
Other comprehensive (loss) income, net of tax	0	0	0	(14,997)	0	(14,997)
Repurchase of Class A common stock (Note 6)	0	0	(60,886)	0	0	(60,886)
Exercise of employee stock options/vesting of stock awards	0	(3,083)	1,676	0	0	(1,407)
Stock-based compensation	0	3,455	0	0	0	3,455
Cash dividends	0	0	0	0	(20,686)	(20,686)
Balance at end of period at Mar. 31, 2020	91	557,916	(1,384,036)	(100,289)	1,726,816	800,498
Balance at beginning of period at Dec. 31, 2020	91	579,801	(1,461,593)	(64,768)	1,840,740	894,271
Stockholders' Equity [Roll Forward]
Net income	0	0	0	0	47,430	47,430
Other comprehensive (loss) income, net of tax	0	0	0	(6,858)	0	(6,858)
Repurchase of Class A common stock (Note 6)	0	0	(50,406)	0	0	(50,406)
Exercise of employee stock options/vesting of stock awards	0	(7,400)	6,923	0	0	(477)
Stock-based compensation	0	6,803	0	0	0	6,803
Cash dividends	0	0	0	0	(19,289)	(19,289)
Balance at end of period at Mar. 31, 2021	$ 91	$ 579,204	$ (1,505,076)	$ (71,626)	$ 1,868,881	$ 871,474