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			13,915		13,915
Foreign currency translation adjustments				1,021	1,021
Change in pension obligation				30	30
Exercise of stock options (in shares)	75
Exercise of stock options		446			446
Issuance of restricted common shares (in shares)	19
Issuance of restricted common shares		(227)			(227)
Stock-based compensation expense		1,132			1,132
Balance (in shares) at Mar. 31, 2018	32,142
Balance at Mar. 31, 2018	$ 32	557,498	(189,230)	3,227	371,527
Increase (Decrease) in Stockholders' Equity
Adjustment to Retained Earnings upon ASC 606 Adoption			1,600		1,600
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			6,062		6,062
Foreign currency translation adjustments				(495)	(495)
Change in pension obligation				30	30
Exercise of stock options (in shares)	288
Exercise of stock options		1,828			1,828
Issuance of restricted common shares (in shares)	35
Issuance of restricted common shares		(281)			(281)
Stock-based compensation expense		1,672			1,672
Balance (in shares) at Mar. 31, 2019	32,881
Balance at Mar. 31, 2019	$ 33	$ 568,335	$ (151,198)	$ (17)	$ 417,153