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	(61,203)	$ 0	0	61,203	0
Shares Issued, Value, Share-based Payment Arrangement, before Forfeiture	0	0	(7,088)	7,898	(810)
Stock-based compensation expense	6,552	0	4,893	1,659	0
Other	642	0	381	261	0
Dividends paid	(15,557)	0	0	0	(15,557)
Unrealized gain (loss) on marketable securities, net of tax	85	0	0	0	85
Net income	62,092	0	0	0	62,092
Balance at Mar. 31, 2020	(3,310)	$ 555	46,327	(595,487)	545,295
Balance (shares) at Mar. 31, 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	(29,686)	$ 0	0	29,686	0
Shares Issued, Value, Share-based Payment Arrangement, before Forfeiture	0	0	(25,085)	26,421	(1,336)
Stock-based compensation expense	11,822	0	10,851	971	0
Stock Issued During Period, Value, Stock Options Exercised	(240)	0	(329)	(569)	0
Other	682	0	364	318	0
Dividends paid	(15,461)	0	0	0	(15,461)
Unrealized gain (loss) on marketable securities, net of tax	(7)	0	0	0	(7)
Net income	61,922	0	0	0	61,922
Balance at Mar. 31, 2021	$ 73,644	$ 555	$ 81,329	$ (628,391)	$ 620,151
Balance (shares) at Mar. 31, 2021		55,489