CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Income [Member]	Retained Earnings [Member]
Beginning Balance (in shares) at Dec. 31, 2015		28,653
Beginning Balance at Dec. 31, 2015	$ 442,590	$ 28	$ 145,366	$ (1,851)	$ 299,047
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		8,479
Repurchase of common stock (in shares)		(146)
Repurchase of common stock	(6,435)		(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
Stock-based compensation expense related to employee stock options and awards	19,599		19,599
Stock-based compensation expense related to employee stock purchases	1,286		1,286
Payment of dividends to stockholders	(15,054)				(15,054)
Unrealized actuarial gain (loss) on pension benefits	(352)			(352)
Unrealized gain (loss) on marketable securities,	(123)			(123)
Translation adjustment	(384)			(384)
Net income (loss)	48,898				48,898
Ending Balance (in shares) at Dec. 31, 2016		29,250
Ending Balance at Dec. 31, 2016	503,084	$ 28	172,875	(2,710)	332,891
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect of New Accounting Principle in Period of Adoption | ASU 2016-09	7,542				7,542
Issuance of common stock under employee stock option and stock award plans (in shares)		569
Issuance of common stock under employee stock option and stock award plans		$ 1
Issuance of common stock under employee stock option and stock award plans	5,087		5,086
Repurchase of common stock (in shares)		(129)
Repurchase of common stock	(9,188)		(9,188)
Issuance of common stock under employee stock purchase plan (in shares)		92
Issuance of common stock under employee stock purchase plan	4,934		4,934
Stock-based compensation expense related to employee stock options and awards	23,337		23,337
Stock-based compensation expense related to employee stock purchases	1,340		1,340
Payment of dividends to stockholders	(16,634)				(16,634)
Unrealized actuarial gain (loss) on pension benefits	699			699
Unrealized gain (loss) on marketable securities,	(207)			(207)
Translation adjustment	79			79
Net income (loss)	27,609				27,609
Ending Balance (in shares) at Dec. 31, 2017		29,782
Ending Balance at Dec. 31, 2017	547,682	$ 29	198,384	(2,139)	351,408
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock option and stock award plans (in shares)		591
Issuance of common stock under employee stock option and stock award plans	4,010		4,010
Repurchase of common stock (in shares)		(1,572)
Repurchase of common stock	(103,154)	$ (1)	(103,153)
Issuance of common stock under employee stock purchase plan (in shares)		88
Issuance of common stock under employee stock purchase plan	5,343		5,343
Stock-based compensation expense related to employee stock options and awards	20,027		20,027
Stock-based compensation expense related to employee stock purchases	1,553		1,553
Payment of dividends to stockholders	(18,823)				(18,823)
Unrealized actuarial gain (loss) on pension benefits	525			525
Unrealized gain (loss) on marketable securities,	161			161
Translation adjustment	(236)			(236)
Net income (loss)	69,984				69,984
Ending Balance (in shares) at Dec. 31, 2018		28,889
Ending Balance at Dec. 31, 2018	$ 527,072	$ 28	$ 126,164	$ (1,689)	$ 402,569