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, 2017	32,048
Balance at Dec. 31, 2017	$ 32	$ 556,147	$ (204,745)	$ 2,176	$ 353,610
Increase (Decrease) in Stockholders' Equity
Net income			45,885		45,885
Adjustment to Retained Earnings upon ASC 606 Adoption			1,600		1,600
Foreign currency translation adjustments				(1,794)	(1,794)
Change in pension obligation, net of tax				66	66
Exercise of stock options (in shares)	273
Exercise of stock options	$ 1	1,733			1,734
Issuance of shares under Employee Stock Purchase Plan (in shares)	55
Issuance of shares under Employee Stock Purchase Plan		1,025			1,025
Issuance of restricted common shares (in shares)	182
Issuance of restricted common shares		(1,419)			(1,419)
Stock-based compensation expense		7,630			7,630
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			17,034		17,034
Foreign currency translation adjustments				(444)	(444)
Change in pension obligation, net of tax				(262)	(262)
Exercise of stock options (in shares)	775
Exercise of stock options	$ 1	5,104			5,105
Issuance of shares under Employee Stock Purchase Plan (in shares)	54
Issuance of shares under Employee Stock Purchase Plan		1,016			1,016
Issuance of restricted common shares (in shares)	250
Issuance of restricted common shares		(1,633)			(1,633)
Stock-based compensation expense		8,018			8,018
Repurchase of common stock (in shares)	(1,052)
Repurchase of common stock	$ (1)	(17,743)			(17,744)
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			49,982		49,982
Foreign currency translation adjustments				3,427	3,427
Change in pension obligation, net of tax				266	266
Exercise of stock options (in shares)	1,001
Exercise of stock options	$ 1	8,418			8,419
Issuance of shares under Employee Stock Purchase Plan (in shares)	41
Issuance of shares under Employee Stock Purchase Plan		1,011			1,011
Issuance of restricted common shares (in shares)	364
Issuance of restricted common shares		(3,915)			(3,915)
Stock-based compensation expense		10,485			10,485
Repurchase of common stock (in shares)	(358)
Repurchase of common stock		(5,775)	(1,725)		(7,500)
Balance (in shares) at Dec. 31, 2020	33,633
Balance at Dec. 31, 2020	$ 34	$ 570,102	$ (91,969)	$ 3,435	$ 481,602