CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Retained Earnings	Total
Beginning Balance (in shares) at Dec. 31, 2018	57,778
Beginning balance at Dec. 31, 2018	$ 28	$ 126,164	$ (1,689)	$ 402,569	$ 527,072
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock option and stock award plans (in shares)	1,130
Issuance of common stock under employee stock option and stock award plans		4,359			4,359
Repurchase of common stock (in shares)	(242)
Repurchase of common stock		(7,302)			(7,302)
Issuance of common stock under employee stock purchase plan (in shares)	196
Issuance of common stock under employee stock purchase plan		5,549			5,549
Stock-based compensation expense related to employee stock options and awards		21,686			21,686
Stock-based compensation expense related to employee stock purchases		1,661			1,661
Payment of dividends to stockholders				(20,506)	(20,506)
Unrealized actuarial gain (loss) on pension benefits			(1,772)		(1,772)
Unrealized (loss) gain on marketable securities			849		849
Foreign currency translation adjustment			(518)		(518)
Net income				193,468	193,468
Ending Balance (in shares) at Dec. 31, 2019	58,862
Ending balance at Dec. 31, 2019	$ 28	152,117	(3,130)	575,531	724,546
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock option and stock award plans (in shares)	963
Issuance of common stock under employee stock option and stock award plans		4,608			4,608
Repurchase of common stock (in shares)	(63)
Repurchase of common stock		(2,636)			(2,636)
Issuance of common stock under employee stock purchase plan (in shares)	148
Issuance of common stock under employee stock purchase plan		5,919			5,919
Stock-based compensation expense related to employee stock options and awards		28,952			28,952
Stock-based compensation expense related to employee stock purchases		1,960			1,960
Payment of dividends to stockholders				(25,081)	(25,081)
Unrealized actuarial gain (loss) on pension benefits			843		843
Unrealized (loss) gain on marketable securities			307		307
Foreign currency translation adjustment			(183)		(183)
Net income				71,176	71,176
Ending Balance (in shares) at Dec. 31, 2020	59,910
Ending balance at Dec. 31, 2020	$ 28	190,920	(2,163)	621,626	810,411
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock option and stock award plans (in shares)	780
Issuance of common stock under employee stock option and stock award plans		1,644			1,644
Repurchase of common stock (in shares)	(878)
Repurchase of common stock	$ (1)	(73,937)			(73,938)
Issuance of common stock under employee stock purchase plan (in shares)	101
Issuance of common stock under employee stock purchase plan	$ 1	6,065			6,066
Stock-based compensation expense related to employee stock options and awards		35,647			35,647
Stock-based compensation expense related to employee stock purchases		1,962			1,962
Payment of dividends to stockholders				(32,599)	(32,599)
Unrealized actuarial gain (loss) on pension benefits			967		967
Unrealized (loss) gain on marketable securities			(2,055)		(2,055)
Foreign currency translation adjustment			(486)		(486)
Net income				164,413	164,413
Ending Balance (in shares) at Dec. 31, 2021	59,913
Ending balance at Dec. 31, 2021	$ 28	$ 162,301	$ (3,737)	$ 753,440	$ 912,032