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, 2014	$ 204,096,000	$ 617,000	$ 137,460,000	$ (148,465,000)	$ 3,000	$ 214,481,000
Balance (shares) at Dec. 31, 2014		61,517
Purchase of treasury stock, at cost	(67,113,000)	$ 0	0	(67,113,000)	0	0
Exercise of stock options	(374,000)	0	(3,000)	(377,000)	0	0
Income tax benefit from stock-based compensation, net	2,216,000	0	2,216,000	0	0	0
Stock-based compensation expense	13,345,000	0	4,239,000	9,053,000	0	53,000
Other	1,303,000	0	480,000	823,000	0	0
Dividends paid	(21,153,000)	0	0	0	0	(21,153,000)
Unrealized gain (loss) on marketable securities, net of tax	(3,000)	0	0	0	(3,000)	0
Net income	39,390,000	0	0	0	0	39,390,000
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