CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]
Balance at Dec. 31, 2015	$ 172,455,000	$ 617,000	$ 144,392,000	$ (205,325,000)	$ 0	$ 232,771,000
Balance (shares) at Dec. 31, 2015		61,517
Purchase of treasury stock, at cost	(31,669,000)	$ 0	0	(31,669,000)	0	0
Repurchase of common stock	(144,263,000)	$ (62,000)	(144,201,000)	0	0	0
Repurchase of common stock (in shares)		(6,028)
Exercise of stock options	598,000	$ 0	(27,000)	625,000	0	0
Stock-based compensation expense	16,643,000	0	8,156,000	8,487,000	0	0
Other	1,372,000	0	642,000	730,000	0	0
Dividends paid	(20,599,000)	0	0	0	0	(20,599,000)
Unrealized gain (loss) on marketable securities, net of tax	(3,000)	0	0	0	(3,000)	0
Net income	65,991,000	0	0	0	0	65,991,000
Balance at Dec. 31, 2016	60,525,000	$ 555,000	8,962,000	(227,152,000)	(3,000)	278,163,000
Balance (shares) at Dec. 31, 2016		55,489
Purchase of treasury stock, at cost	(38,735,000)	$ 0	0	(38,735,000)	0	0
Stock-based compensation expense	24,345,000	0	15,508,000	8,837,000	0	0
Other	1,554,000	0	867,000	687,000	0	0
Dividends paid	(65,768,000)	0	0	0	0	(65,768,000)
Unrealized gain (loss) on marketable securities, net of tax	(2,000)	0	0	0	(2,000)	0
Net income	84,402,000	0	0	0	0	84,402,000
Balance at Dec. 31, 2017	66,321,000	$ 555,000	25,337,000	(256,363,000)	(5,000)	296,797,000
Balance (shares) at Dec. 31, 2017		55,489
Purchase of treasury stock, at cost	(113,327,000)	$ 0	0	(113,327,000)	0	0
Stock-based compensation expense	20,425,000	0	9,696,000	11,584,000	0	(855,000)
Other	2,256,000	0	1,719,000	537,000	0	0
Dividends paid	(33,408,000)	0	0	0	0	(33,408,000)
Unrealized gain (loss) on marketable securities, net of tax	(4,000)	0	0	0	(4,000)	0
Net income	135,413,000	0	0	0	0	135,413,000
Balance at Dec. 31, 2018	$ 77,676,000	$ 555,000	$ 36,752,000	$ (357,569,000)	$ (9,000)	$ 397,947,000
Balance (shares) at Dec. 31, 2018		55,489