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	Cumulative Effect Adjustment [Member] Common Stock [Member] Class A [Member]	Cumulative Effect Adjustment [Member] Additional Paid-in Capital [Member]	Cumulative Effect Adjustment [Member] Treasury Stock [Member]	Cumulative Effect Adjustment [Member] Accumulated Other Comprehensive Loss [Member]	Cumulative Effect Adjustment [Member] Retained Earnings [Member]	Cumulative Effect Adjustment [Member]
Balance at beginning of period at Dec. 31, 2018	$ 91	$ 552,564	$ (1,326,605)	$ (79,934)	$ 1,635,751	$ 781,867
Balance at beginning of period (ASC 842 [Member]) at Dec. 31, 2018							$ 0	$ 0	$ 0	$ 0	$ 657	$ 657
Stockholders' Equity [Roll Forward]
Net income	0	0	0	0	133,441	133,441
Other comprehensive (loss) income, net of tax	0	0	0	(15,027)	0	(15,027)
Repurchase of Class A common stock (Note 6)	0	0	(825)	0	0	(825)
Exercise of employee stock options/vesting of stock awards	0	(4,930)	2,604	0	0	(2,326)
Stock-based compensation	0	9,649	0	0	0	9,649
Cash dividends	0	0	0	0	(61,636)	(61,636)
Balance at end of period at Sep. 30, 2019	91	557,283	(1,324,826)	(94,961)	1,708,213	845,800
Balance at beginning of period at Jun. 30, 2019	91	556,294	(1,324,834)	(81,276)	1,684,675	834,950
Stockholders' Equity [Roll Forward]
Net income	0	0	0	0	44,090	44,090
Other comprehensive (loss) income, net of tax	0	0	0	(13,685)	0	(13,685)
Repurchase of Class A common stock (Note 6)	0	0	0	0	0	0
Exercise of employee stock options/vesting of stock awards	0	(26)	8	0	0	(18)
Stock-based compensation	0	1,015	0	0	0	1,015
Cash dividends	0	0	0	0	(20,552)	(20,552)
Balance at end of period at Sep. 30, 2019	91	557,283	(1,324,826)	(94,961)	1,708,213	845,800
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