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, 2017	$ 66,321	$ 555	$ 25,337	$ (256,363)	$ 296,792
Balance (shares) at Dec. 31, 2017		55,489
Purchase of treasury stock, at cost	(16,236)	$ 0	0	(16,236)	0
Issuance of long-term incentive awards and dividend equivalents	0	0	(5,764)	6,619	(855)
Stock-based compensation expense	14,656	0	11,293	3,363	0
Other	1,611	0	1,181	430	0
Dividends paid	(25,170)	0	0	0	(25,170)
Unrealized gain (loss) on marketable securities, net of tax	(20)	0	0	0	(20)
Net income	110,758	0	0	0	110,758
Balance at Sep. 30, 2018	151,920	$ 555	32,047	(262,187)	381,505
Balance (shares) at Sep. 30, 2018		55,489
Balance at Jun. 30, 2018	117,860	$ 555	27,363	(263,764)	353,706
Balance (shares) at Jun. 30, 2018		55,489
Purchase of treasury stock, at cost	(9)	$ 0	0	(9)	0
Stock-based compensation expense	5,769	0	4,288	1,481	0
Other	501	0	396	105	0
Dividends paid	(8,384)	0	0	0	(8,384)
Unrealized gain (loss) on marketable securities, net of tax	(24)	0	0	0	(24)
Net income	36,207	0	0	0	36,207
Balance at Sep. 30, 2018	151,920	$ 555	32,047	(262,187)	381,505
Balance (shares) at Sep. 30, 2018		55,489
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