Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Treasury Stock	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Total
Balance (in shares) at Dec. 31, 2015	29,026
Balance at Dec. 31, 2015	$ 29	$ 529,089	$ (1,218)	$ (342,705)	$ (1,431)	$ 183,764
Increase (Decrease) in Stockholders' Equity
Net income				11,001		11,001
Foreign currency translation adjustments					(847)	(847)
Change in pension obligation					(1)	(1)
Exercise of stock options (in shares)	392
Exercise of stock options	$ 1	2,237				2,238
Issuance of shares under Employee Stock Purchase Plan (in shares)	22
Issuance of shares under Employee Stock Purchase Plan		325				325
Issuance of restricted common shares (in shares)	108
Issuance of restricted common shares		(11)				(11)
Treasury shares returned to authorized (in shares)	(30)
Treasury shares returned to authorized		(1,218)	$ 1,218
Reverse stock split issuance costs		(145)				(145)
Stock-based compensation expense		5,131				5,131
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