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	117,888	117,888
Other comprehensive (loss) income, net of tax	0	0	0	2,184	0	2,184
Repurchase of Class A common stock (Note 6)	0	0	(127,361)	0	0	(127,361)
Exercise of employee stock options/vesting of stock awards	0	(2,492)	5,813	0	0	3,321
Stock-based compensation	0	15,439	0	0	0	15,439
Cash dividends	0	0	0	0	(59,287)	(59,287)
Balance at end of period at Sep. 30, 2020	91	570,491	(1,446,374)	(83,108)	1,786,373	827,473
Balance at beginning of period at Jun. 30, 2020	91	563,115	(1,427,064)	(93,441)	1,749,311	792,012
Stockholders' Equity [Roll Forward]
Net income	0	0	0	0	56,307	56,307
Other comprehensive (loss) income, net of tax	0	0	0	10,333	0	10,333
Repurchase of Class A common stock (Note 6)	0	0	(19,994)	0	0	(19,994)
Exercise of employee stock options/vesting of stock awards	0	261	684	0	0	945
Stock-based compensation	0	7,115	0	0	0	7,115
Cash dividends	0	0	0	0	(19,245)	(19,245)
Balance at end of period at Sep. 30, 2020	91	570,491	(1,446,374)	(83,108)	1,786,373	827,473
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	156,497	156,497
Other comprehensive (loss) income, net of tax	0	0	0	(10,890)	0	(10,890)
Repurchase of Class A common stock (Note 6)	0	0	(70,415)	0	0	(70,415)
Exercise of employee stock options/vesting of stock awards	0	(5,599)	13,473	0	0	7,874
Stock-based compensation	0	16,476	0	0	0	16,476
Cash dividends	0	0	0	0	(57,336)	(57,336)
Balance at end of period at Sep. 30, 2021	91	590,678	(1,518,535)	(75,658)	1,939,901	936,477
Balance at beginning of period at Jun. 30, 2021	91	586,976	(1,509,867)	(68,553)	1,909,179	917,826
Stockholders' Equity [Roll Forward]
Net income	0	0	0	0	49,729	49,729
Other comprehensive (loss) income, net of tax	0	0	0	(7,105)	0	(7,105)
Repurchase of Class A common stock (Note 6)	0	0	(10,005)	0	0	(10,005)
Exercise of employee stock options/vesting of stock awards	0	609	1,337	0	0	1,946
Stock-based compensation	0	3,093	0	0	0	3,093
Cash dividends	0	0	0	0	(19,007)	(19,007)
Balance at end of period at Sep. 30, 2021	$ 91	$ 590,678	$ (1,518,535)	$ (75,658)	$ 1,939,901	$ 936,477