CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Employee Stock Options and Awards [Member]	Employee Stock Purchases [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Additional Paid-In Capital [Member] Employee Stock Options and Awards [Member]	Additional Paid-In Capital [Member] Employee Stock Purchases [Member]	Accumulated Other Comprehensive Income [Member]	Retained Earnings [Member]
Beginning Balance (in shares) at Dec. 31, 2012				28,536
Beginning Balance at Dec. 31, 2012	$ 341,049			$ 28	$ 175,668			$ (293)	$ 165,646
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock option and stock award plans (in shares)				1,358
Issuance of common stock under employee stock option and stock award plans	26,269			$ 2	26,267
Issuance of common stock under employee stock purchase plan (in shares)				128
Issuance of common stock under employee stock purchase plan	3,971				3,971
Income tax benefits from employee stock plans	1,284				1,284
Stock-based compensation expense		$ 15,275	$ 1,195			$ 15,275	$ 1,195
Payment of dividends to stockholders	(9,446)								(9,446)
Unrealized actuarial loss on pension benefits, net of tax	(220)							(220)
Unrealized gain (loss) on marketable securities,	72							72
Translation adjustment	(29)							(29)
Net income	57,266								57,266
Ending Balance (in shares) at Dec. 31, 2013				30,022
Ending Balance at Dec. 31, 2013	436,686			$ 30	223,660			(470)	213,466
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock option and stock award plans (in shares)				697
Issuance of common stock under employee stock option and stock award plans	9,571			$ 0	9,571
Repurchase of common stock (in shares)				(1,603)
Repurchase of common stock	(80,761)			$ (1)	(80,760)
Issuance of common stock under employee stock purchase plan (in shares)				92
Issuance of common stock under employee stock purchase plan	4,284				4,284
Income tax benefits from employee stock plans	815				815
Stock-based compensation expense		12,983	1,385			12,983	1,385
Payment of dividends to stockholders	(13,165)								(13,165)
Unrealized actuarial loss on pension benefits, net of tax	(460)							(460)
Unrealized gain (loss) on marketable securities,	(127)							(127)
Translation adjustment	(79)							(79)
Net income	59,544								59,544
Ending Balance (in shares) at Dec. 31, 2014				29,208
Ending Balance at Dec. 31, 2014	430,676			$ 29	171,938			(1,136)	259,845
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock option and stock award plans (in shares)				578
Issuance of common stock under employee stock option and stock award plans	8,133			$ 0	8,133
Repurchase of common stock (in shares)				(1,250)
Repurchase of common stock	(53,731)			$ (1)	(53,730)
Issuance of common stock under employee stock purchase plan (in shares)				117
Issuance of common stock under employee stock purchase plan	4,447				4,447
Income tax shortfall from employee stock plans	(189)				(189)
Stock-based compensation expense		$ 13,562	$ 1,205			$ 13,562	$ 1,205
Payment of dividends to stockholders	(13,916)								(13,916)
Unrealized actuarial loss on pension benefits, net of tax	(344)							(344)
Unrealized gain (loss) on marketable securities,	(180)							(180)
Translation adjustment	(191)							(191)
Net income	39,147								39,147
Ending Balance (in shares) at Dec. 31, 2015				28,653
Ending Balance at Dec. 31, 2015	$ 428,619			$ 28	$ 145,366			$ (1,851)	$ 285,076