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	(91,216)	$ 0	0	91,216	0
Issuance of equity-based incentive awards and dividend equivalents	0	0	(7,088)	7,898	(810)
Stock-based compensation expense	38,110	0	32,893	5,217	0
Other	2,217	0	652	1,565	0
Dividends paid	(46,522)	0	0	0	(46,522)
Unrealized gain (loss) on marketable securities, net of tax	19	0	0	0	19
Net income	133,952	0	0	0	133,952
Balance at Sep. 30, 2020	40,639	$ 555	74,598	(620,638)	586,124
Balance (shares) at Sep. 30, 2020		55,489
Balance at Jun. 30, 2020	44,638	$ 555	54,783	(592,313)	581,613
Balance (shares) at Jun. 30, 2020		55,489
Purchase of treasury stock, at cost	(29,986)	$ 0	0	29,986	0
Stock-based compensation expense	20,864	0	19,552	1,312	0
Other	612	0	263	349	0
Dividends paid	(15,448)	0	0	0	(15,448)
Unrealized gain (loss) on marketable securities, net of tax	(50)	0	0	0	(50)
Net income	20,009	0	0	0	20,009
Balance at Sep. 30, 2020	40,639	$ 555	74,598	(620,638)	586,124
Balance (shares) at Sep. 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	(49,770)	$ 0	0	49,770	0
Issuance of equity-based incentive awards and dividend equivalents	0	0	(25,112)	26,449	(1,337)
Stock-based compensation expense	35,965	0	33,266	2,699	0
Stock Issued During Period, Value, Stock Options Exercised	(240)	0	(329)	(569)	0
Other	2,278	0	1,234	1,044	0
Dividends paid	(50,198)	0	0	0	(50,198)
Unrealized gain (loss) on marketable securities, net of tax	(13)	0	0	0	(13)
Net income	114,372	0	0	0	114,372
Balance at Sep. 30, 2021	97,006	$ 555	104,587	(645,993)	637,857
Balance (shares) at Sep. 30, 2021		55,489
Balance at Jun. 30, 2021	87,262	$ 555	94,396	(635,627)	627,938
Balance (shares) at Jun. 30, 2021		55,489
Purchase of treasury stock, at cost	(11,234)	$ 0	0	11,234	0
Issuance of equity-based incentive awards and dividend equivalents	0	0	(27)	28	(1)
Stock-based compensation expense	10,362	0	9,827	535	0
Other	696	0	391	305	0
Dividends paid	(17,369)	0	0	0	(17,369)
Unrealized gain (loss) on marketable securities, net of tax	(7)	0	0	0	(7)
Net income	27,296	0	0	0	27,296
Balance at Sep. 30, 2021	$ 97,006	$ 555	$ 104,587	$ (645,993)	$ 637,857
Balance (shares) at Sep. 30, 2021		55,489