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, 2018	32,558
Balance at Dec. 31, 2018	$ 33	$ 565,116	$ (157,260)	$ 448	$ 408,337
Increase (Decrease) in Stockholders' Equity
Net income			6,062		6,062
Foreign currency translation adjustments				(495)	(495)
Change in pension obligation				30	30
Exercise of stock options (in shares)	288
Exercise of stock options		1,828			1,828
Issuance of restricted common shares, net of shares withheld (in shares)	35
Issuance of restricted common shares, net of shares withheld		(281)			(281)
Stock-based compensation expense		1,672			1,672
Balance (in shares) at Mar. 31, 2019	32,881
Balance at Mar. 31, 2019	$ 33	568,335	(151,198)	(17)	417,153
Balance (in shares) at Dec. 31, 2018	32,558
Balance at Dec. 31, 2018	$ 33	565,116	(157,260)	448	408,337
Increase (Decrease) in Stockholders' Equity
Net income					7,322
Foreign currency translation adjustments					(1,847)
Change in pension obligation					89
Balance (in shares) at Sep. 30, 2019	32,397
Balance at Sep. 30, 2019	$ 32	559,063	(149,938)	(1,310)	407,847
Balance (in shares) at Mar. 31, 2019	32,881
Balance at Mar. 31, 2019	$ 33	568,335	(151,198)	(17)	417,153
Increase (Decrease) in Stockholders' Equity
Net income			556		556
Foreign currency translation adjustments				(219)	(219)
Change in pension obligation				29	29
Exercise of stock options (in shares)	104
Exercise of stock options		567			567
Issuance of shares under Employee Stock Purchase Plan (in shares)	32
Issuance of shares under Employee Stock Purchase Plan		479			479
Issuance of restricted common shares, net of shares withheld (in shares)	165
Issuance of restricted common shares, net of shares withheld		(1,310)			(1,310)
Stock-based compensation expense		2,246			2,246
Repurchase of common stock (in shares)	(885)
Repurchase of common stock	$ (1)	(14,034)			(14,035)
Balance (in shares) at Jun. 30, 2019	32,297
Balance at Jun. 30, 2019	$ 32	556,283	(150,642)	(207)	405,466
Increase (Decrease) in Stockholders' Equity
Net income			704		704
Foreign currency translation adjustments				(1,132)	(1,132)
Change in pension obligation				29	29
Exercise of stock options (in shares)	97
Exercise of stock options		642			642
Issuance of restricted common shares, net of shares withheld (in shares)	3
Issuance of restricted common shares, net of shares withheld		(11)			(11)
Stock-based compensation expense		2,149			2,149
Balance (in shares) at Sep. 30, 2019	32,397
Balance at Sep. 30, 2019	$ 32	559,063	(149,938)	(1,310)	407,847
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)	1
Exercise of stock options	$ 540	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 restricted common shares, net of shares withheld (in shares)	69
Issuance of restricted common shares, net of shares withheld		(1,162)			(1,162)
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	33
Balance at Mar. 31, 2020	$ 32,837	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	33
Balance at Mar. 31, 2020	$ 32,837	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 restricted common shares, net of shares withheld (in shares)	232
Issuance of restricted common shares, net of shares withheld		(2,698)			(2,698)
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
Exercise of stock options		458			458
Issuance of restricted common shares, net of shares withheld (in shares)	5
Issuance of restricted common shares, net of shares withheld		(28)			(28)
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