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, 2018	$ 77,676	$ 555	$ 36,752	$ (357,569)	$ 397,938
Balance (shares) at Dec. 31, 2018		55,489
Purchase of treasury stock, at cost	(153,668)	$ 0	0	(153,668)	0
Issuance of long-term incentive awards and dividend equivalents	0	0	(7,695)	8,646	(951)
Stock-based compensation expense	20,813	0	15,656	5,157	0
Other	2,205	0	1,688	517	0
Dividends paid	(36,777)	0	0	0	(36,777)
Unrealized gain (loss) on marketable securities, net of tax	35	0	0	0	35
Net income	130,704	0	0	0	130,704
Balance at Sep. 30, 2019	40,988	$ 555	46,401	(496,917)	490,949
Balance (shares) at Sep. 30, 2019		55,489
Balance at Jun. 30, 2019	134,889	$ 555	41,009	(383,830)	477,155
Balance (shares) at Jun. 30, 2019		55,489
Purchase of treasury stock, at cost	(114,872)	$ 0	0	(114,872)	0
Stock-based compensation expense	6,517	0	4,880	1,637	0
Other	660	0	512	148	0
Dividends paid	(12,037)	0	0	0	(12,037)
Unrealized gain (loss) on marketable securities, net of tax	(28)	0	0	0	(28)
Net income	25,859	0	0	0	25,859
Balance at Sep. 30, 2019	40,988	$ 555	46,401	(496,917)	490,949
Balance (shares) at Sep. 30, 2019		55,489
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 long-term 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