Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock	Additional Paid-in Capital	Treasury Stock	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Total
Balance at Dec. 31, 2012	$ 108	$ 504,643	$ (1,218)	$ (322,477)	$ 5,020	$ 186,076
Balance (in shares) at Dec. 31, 2012	108,293
Increase (Decrease) in Stockholders' Equity
Net income (loss)				(17,144)		(17,144)
Foreign currency translation adjustments					695	695
Change in pension obligation					24	24
Exercise of stock options	$ 2	1,667				1,669
Exercise of stock options (in shares)	1,511
Issuance of shares under Employee Stock Purchase Plan		436				436
Issuance of shares under Employee Stock Purchase Plan (in shares)	206
Issuance of restricted common shares		(26)				(26)
Issuance of restricted common shares (in shares)	215
Stock-based compensation expense		4,272				4,272
Balance at Dec. 31, 2013	$ 110	510,992	(1,218)	(339,621)	5,739	176,002
Balance (in shares) at Dec. 31, 2013	110,225
Increase (Decrease) in Stockholders' Equity
Net income (loss)				(11,266)		(11,266)
Foreign currency translation adjustments					(4,150)	(4,150)
Change in pension obligation					(313)	(313)
Exercise of stock options	$ 3	2,892				2,895
Exercise of stock options (in shares)	2,418
Issuance of shares under Employee Stock Purchase Plan		446				446
Issuance of shares under Employee Stock Purchase Plan (in shares)	199
Issuance of restricted common shares		(7)				(7)
Issuance of restricted common shares (in shares)	7
Stock-based compensation expense		4,745				4,745
Balance at Dec. 31, 2014	$ 113	519,068	(1,218)	(350,887)	1,276	168,352
Balance (in shares) at Dec. 31, 2014	112,849
Increase (Decrease) in Stockholders' Equity
Net income (loss)				14,678		14,678
Foreign currency translation adjustments					(2,664)	(2,664)
Change in pension obligation					(43)	(43)
Exercise of stock options	$ 3	3,918				3,921
Exercise of stock options (in shares)	3,036
Issuance of shares under Employee Stock Purchase Plan		441				441
Issuance of shares under Employee Stock Purchase Plan (in shares)	188
Issuance of restricted common shares		(7)				(7)
Issuance of restricted common shares (in shares)	28
Stock-based compensation expense		5,582				5,582
Balance at Dec. 31, 2015	$ 116	$ 529,002	$ (1,218)	$ (336,209)	$ (1,431)	$ 190,260
Balance (in shares) at Dec. 31, 2015	116,101