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, 2016	29,518
Balance at Dec. 31, 2016	$ 30	$ 535,408	$ (331,704)	$ (2,279)	$ 201,455
Increase (Decrease) in Stockholders' Equity
Net income			126,959		126,959
Foreign currency translation adjustments				4,347	4,347
Change in pension obligation				108	108
Exercise of stock options (in shares)	2,358
Exercise of stock options	$ 2	15,512			15,514
Issuance of shares under Employee Stock Purchase Plan (in shares)	34
Issuance of shares under Employee Stock Purchase Plan		845			845
Issuance of restricted common shares (in shares)	138
Issuance of restricted common shares		(1,164)			(1,164)
Stock-based compensation expense		5,546			5,546
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
Foreign currency translation adjustments				(1,794)	(1,794)
Change in pension obligation				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
Adjustment to Retained Earnings upon ASC 606 Adoption			1,600		1,600
Net income			17,034		17,034
Foreign currency translation adjustments				(444)	(444)
Change in pension obligation				(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