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, net of tax				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 restricted common shares (in shares)	69
Issuance of restricted common shares		(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	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					24,523
Foreign currency translation adjustments					(276)
Change in pension obligation, net of tax					114
Balance (in shares) at Jun. 30, 2020	33,433
Balance at Jun. 30, 2020	$ 33	562,839	(117,428)	(420)	445,024
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, net of tax				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 (in shares)	232
Issuance of restricted common shares		(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
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, net of tax				20	20
Exercise of stock options (in shares)	268
Exercise of stock options		2,512			2,512
Issuance of restricted common shares (in shares)	81
Issuance of restricted common shares		(2,354)			(2,354)
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					35,386
Foreign currency translation adjustments					(820)
Change in pension obligation, net of tax					54
Balance (in shares) at Jun. 30, 2021	33,657
Balance at Jun. 30, 2021	$ 34	561,680	(70,281)	2,669	494,102
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, net of tax				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 restricted common shares (in shares)	214
Issuance of restricted common shares		(4,141)			(4,141)
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