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	(38,796)	$ 0	0	(38,796)	0
Issuance of long-term incentive awards and dividend equivalents	0	0	(7,695)	8,646	(951)
Stock-based compensation expense	14,296	0	10,776	3,520	0
Other	1,545	0	1,176	369	0
Dividends paid	(24,740)	0	0	0	(24,740)
Unrealized gain (loss) on marketable securities, net of tax	63	0	0	0	63
Net income	104,845	0	0	0	104,845
Balance at Jun. 30, 2019	134,889	$ 555	41,009	(383,830)	477,155
Balance (shares) at Jun. 30, 2019		55,489
Balance at Mar. 31, 2019	119,194	$ 555	33,833	(376,097)	460,903
Balance (shares) at Mar. 31, 2019		55,489
Purchase of treasury stock, at cost	(9,759)	$ 0	0	(9,759)	0
Stock-based compensation expense	8,256	0	6,436	1,820	0
Other	946	0	740	206	0
Dividends paid	(12,354)	0	0	0	(12,354)
Unrealized gain (loss) on marketable securities, net of tax	50	0	0	0	50
Net income	28,556	0	0	0	28,556
Balance at Jun. 30, 2019	134,889	$ 555	41,009	(383,830)	477,155
Balance (shares) at Jun. 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	(61,230)	$ 0	0	(61,230)	0
Issuance of long-term 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