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, 2013				30,022
Beginning 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
Adjustment to Additional Paid in Capital, Income Tax Effect from Share-based Compensation, Net	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
Adjustment to Additional Paid in Capital, Income Tax Effect from Share-based Compensation, Net	(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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock option and stock award plans (in shares)				615
Issuance of common stock under employee stock option and stock award plans	8,479			$ 0	8,479
Repurchase of common stock (in shares)				(146)
Repurchase of common stock	(6,435)			$ 0	(6,435)
Issuance of common stock under employee stock purchase plan (in shares)				128
Issuance of common stock under employee stock purchase plan	4,580				4,580
Adjustment to Additional Paid in Capital, Income Tax Effect from Share-based Compensation, Net	0
Stock-based compensation expense		$ 19,599	$ 1,286			$ 19,599	$ 1,286
Payment of dividends to stockholders	(15,054)								(15,054)
Unrealized actuarial loss on pension benefits, net of tax	(352)							(352)
Unrealized gain (loss) on marketable securities,	(123)							(123)
Translation adjustment	(384)							(384)
Net income	47,890								47,890
Ending Balance (in shares) at Dec. 31, 2016				29,250
Ending Balance at Dec. 31, 2016	$ 488,105			$ 28	$ 172,875			$ (2,710)	$ 317,912