Consolidated Statements of Stockholders' Equity - 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, 2017	$ 91	$ 466,349	$ (1,304,694)	$ (66,318)	$ 1,609,168	$ 704,596
Balance at beginning of period (ASC 606 [Member]) at Dec. 31, 2017							$ 0	$ 0	$ 0	$ 0	$ (13,042)	$ (13,042)
Balance at beginning of period (ASU 2018-02 [Member]) at Dec. 31, 2017							0	0	0	0	(1,681)	(1,681)
Stockholders' Equity [Roll Forward]
Net income	0	0	0	0	121,887	121,887
Other comprehensive income, net of tax	0	0	0	(13,616)	0	(13,616)
Repurchase of Class A common stock (Note 8)	0	0	(69,565)	0	0	(69,565)
Exercise of employee stock options/vesting of stock awards	0	2,804	7,973	0	0	10,777
Stock-based compensation	0	26,609	0	0	0	26,609
Business Acquisition	0	80,064	19,794	0	0	99,858
Equity component of convertible note settlement (net)	0	(23,262)	19,887	0	0	(3,375)
Cash dividends	0	0	0	0	(80,581)	(80,581)
Balance at end of period at Dec. 31, 2018	91	552,564	(1,326,605)	(79,934)	1,635,751	781,867
Balance at end 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	173,553	173,553
Other comprehensive income, net of tax	0	0	0	(5,358)	0	(5,358)
Repurchase of Class A common stock (Note 8)	0	0	(825)	0	0	(825)
Exercise of employee stock options/vesting of stock awards	0	(4,929)	2,604	0	0	(2,325)
Stock-based compensation	0	9,909	0	0	0	9,909
Cash dividends	0	0	0	0	(82,189)	(82,189)
Balance at end 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	191,355	191,355
Other comprehensive income, net of tax	0	0	0	20,524	0	20,524
Repurchase of Class A common stock (Note 8)	0	0	(144,334)	0	0	(144,334)
Exercise of employee stock options/vesting of stock awards	0	(1,803)	7,567	0	0	5,764
Stock-based compensation	0	24,060	0	0	0	24,060
Cash dividends	0	0	0	0	(78,387)	(78,387)
Balance at end of period at Dec. 31, 2020	$ 91	$ 579,801	$ (1,461,593)	$ (64,768)	$ 1,840,740	$ 894,271