CONSOLIDATED STATEMENT OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]
Balance at Dec. 31, 2019	$ 4,079	$ 555	$ 48,141	$ (544,102)	$ 499,485
Balance (shares) at Dec. 31, 2019		55,489
Purchase of treasury stock, at cost	(61,230)	$ 0	0	61,230	0
Issuance of equity-based incentive awards and dividend equivalents	0	0	(7,088)	7,898	(810)
Stock-based compensation expense	17,246	0	13,341	3,905	0
Other	1,605	0	389	1,216	0
Dividends paid	(31,074)	0	0	0	(31,074)
Unrealized gain (loss) on marketable securities, net of tax	69	0	0	0	69
Net income	113,943	0	0	0	113,943
Balance at Jun. 30, 2020	44,638	$ 555	54,783	(592,313)	581,613
Balance (shares) at Jun. 30, 2020		55,489
Balance at Mar. 31, 2020	(3,310)	$ 555	46,327	(595,487)	545,295
Balance (shares) at Mar. 31, 2020		55,489
Purchase of treasury stock, at cost	(27)	$ 0	0	27	0
Stock-based compensation expense	10,694	0	8,448	2,246	0
Other	963	0	8	955	0
Dividends paid	(15,517)	0	0	0	(15,517)
Unrealized gain (loss) on marketable securities, net of tax	(16)	0	0	0	(16)
Net income	51,851	0	0	0	51,851
Balance at Jun. 30, 2020	44,638	$ 555	54,783	(592,313)	581,613
Balance (shares) at Jun. 30, 2020		55,489
Balance at Dec. 31, 2020	44,132	$ 555	95,528	(626,984)	575,033
Balance (shares) at Dec. 31, 2020		55,489
Purchase of treasury stock, at cost	(38,536)	$ 0	0	38,536	0
Issuance of equity-based incentive awards and dividend equivalents	0	0	(25,085)	26,421	(1,336)
Stock-based compensation expense	25,603	0	23,439	2,164	0
Stock Issued During Period, Value, Stock Options Exercised	(240)	0	(329)	(569)	0
Other	1,582	0	843	739	0
Dividends paid	(32,828)	0	0	0	(32,828)
Unrealized gain (loss) on marketable securities, net of tax	(7)	0	0	0	(7)
Net income	87,076	0	0	0	87,076
Balance at Jun. 30, 2021	87,262	$ 555	94,396	(635,627)	627,938
Balance (shares) at Jun. 30, 2021		55,489
Balance at Mar. 31, 2021	73,644	$ 555	81,329	(628,391)	620,151
Balance (shares) at Mar. 31, 2021		55,489
Purchase of treasury stock, at cost	(8,850)	$ 0	0	8,850	0
Stock-based compensation expense	13,781	0	12,588	1,193	0
Other	900	0	479	421	0
Dividends paid	(17,367)	0	0	0	(17,367)
Net income	25,154	0	0	0	25,154
Balance at Jun. 30, 2021	$ 87,262	$ 555	$ 94,396	$ (635,627)	$ 627,938
Balance (shares) at Jun. 30, 2021		55,489