Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Total
Balance (in shares) at Dec. 31, 2019	32,585
Balance at Dec. 31, 2019	$ 33	$ 559,878	$ (140,226)	$ (258)	$ 419,427
Increase (Decrease) in Stockholders' Equity
Net income			11,221		11,221
Foreign currency translation adjustments				(1,112)	(1,112)
Change in pension obligation				57	57
Exercise of stock options (in shares)	540
Exercise of stock options	$ 1	4,498			4,499
Issuance of shares under Employee Stock Purchase Plan (in shares)	1
Issuance of shares under Employee Stock Purchase Plan		19			19
Issuance of common shares on restricted stock units, net of shares withheld		(1,162)			(1,162)
Issuance of common shares on restricted stock units, net of shares withheld (in shares)	69
Stock-based compensation expense		1,724			1,724
Repurchase of common stock (in shares)	(358)
Repurchase of common stock	$ (1)	(5,775)	(1,725)		(7,501)
Balance (in shares) at Mar. 31, 2020	32,837
Balance at Mar. 31, 2020	$ 33	559,182	(130,730)	(1,313)	427,172
Balance (in shares) at Dec. 31, 2019	32,585
Balance at Dec. 31, 2019	$ 33	559,878	(140,226)	(258)	419,427
Increase (Decrease) in Stockholders' Equity
Net income					35,308
Foreign currency translation adjustments					1,161
Change in pension obligation					175
Balance (in shares) at Sep. 30, 2020	33,491
Balance at Sep. 30, 2020	$ 33	566,195	(106,643)	1,078	460,663
Balance (in shares) at Mar. 31, 2020	32,837
Balance at Mar. 31, 2020	$ 33	559,182	(130,730)	(1,313)	427,172
Increase (Decrease) in Stockholders' Equity
Net income			13,302		13,302
Foreign currency translation adjustments				836	836
Change in pension obligation				57	57
Exercise of stock options (in shares)	343
Exercise of stock options		2,783			2,783
Issuance of shares under Employee Stock Purchase Plan (in shares)	21
Issuance of shares under Employee Stock Purchase Plan		490			490
Issuance of common shares on restricted stock units, net of shares withheld		(2,698)			(2,698)
Issuance of common shares on restricted stock units, net of shares withheld (in shares)	232
Stock-based compensation expense		3,082			3,082
Balance (in shares) at Jun. 30, 2020	33,433
Balance at Jun. 30, 2020	$ 33	$ 562,839	(117,428)	(420)	445,024
Increase (Decrease) in Stockholders' Equity
Net income			10,785		10,785
Foreign currency translation adjustments				1,437	1,437
Change in pension obligation				61	$ 61
Exercise of stock options (in shares)	53	458			458
Issuance of common shares on restricted stock units, net of shares withheld		$ (28)			$ (28)
Issuance of common shares on restricted stock units, net of shares withheld (in shares)	5
Stock-based compensation expense		2,926			2,926
Balance (in shares) at Sep. 30, 2020	33,491
Balance at Sep. 30, 2020	$ 33	566,195	(106,643)	1,078	460,663
Balance (in shares) at Dec. 31, 2020	33,633
Balance at Dec. 31, 2020	$ 34	570,102	(91,969)	3,435	481,602
Increase (Decrease) in Stockholders' Equity
Net income			16,480		16,480
Foreign currency translation adjustments				(1,372)	(1,372)
Change in pension obligation				20	20
Exercise of stock options (in shares)	268
Exercise of stock options		2,512			2,512
Issuance of common shares on restricted stock units, net of shares withheld		(2,354)			(2,354)
Issuance of common shares on restricted stock units, net of shares withheld (in shares)	81
Stock-based compensation expense		2,407			2,407
Repurchase of common stock (in shares)	(303)
Repurchase of common stock		(5,468)	(6,167)		(11,635)
Balance (in shares) at Mar. 31, 2021	33,679
Balance at Mar. 31, 2021	$ 34	567,199	(81,656)	2,083	487,660
Balance (in shares) at Dec. 31, 2020	33,633
Balance at Dec. 31, 2020	$ 34	570,102	(91,969)	3,435	481,602
Increase (Decrease) in Stockholders' Equity
Net income					62,901
Foreign currency translation adjustments					(1,769)
Change in pension obligation					84
Balance (in shares) at Sep. 30, 2021	33,406
Balance at Sep. 30, 2021	$ 33	559,913	(50,017)	1,750	511,679
Balance (in shares) at Mar. 31, 2021	33,679
Balance at Mar. 31, 2021	$ 34	567,199	(81,656)	2,083	487,660
Increase (Decrease) in Stockholders' Equity
Net income			18,906		18,906
Foreign currency translation adjustments				552	552
Change in pension obligation				34	34
Exercise of stock options (in shares)	72
Exercise of stock options		563			563
Issuance of shares under Employee Stock Purchase Plan (in shares)	15
Issuance of shares under Employee Stock Purchase Plan		509			509
Issuance of common shares on restricted stock units, net of shares withheld		(4,141)			(4,141)
Issuance of common shares on restricted stock units, net of shares withheld (in shares)	214
Stock-based compensation expense		3,377			3,377
Repurchase of common stock (in shares)	(323)
Repurchase of common stock		(5,827)	(7,531)		(13,358)
Balance (in shares) at Jun. 30, 2021	33,657
Balance at Jun. 30, 2021	$ 34	561,680	(70,281)	2,669	494,102
Increase (Decrease) in Stockholders' Equity
Net income			27,515		27,515
Foreign currency translation adjustments				(949)	(949)
Change in pension obligation				30	30
Exercise of stock options (in shares)	34
Exercise of stock options		344			344
Issuance of common shares on restricted stock units, net of shares withheld		(48)			(48)
Issuance of common shares on restricted stock units, net of shares withheld (in shares)	6
Stock-based compensation expense		3,186			3,186
Repurchase of common stock (in shares)	(291)
Repurchase of common stock	$ (1)	(5,249)	(7,251)		(12,501)
Balance (in shares) at Sep. 30, 2021	33,406
Balance at Sep. 30, 2021	$ 33	$ 559,913	$ (50,017)	$ 1,750	$ 511,679