Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Non-Controlling Interest [Member]
Beginning Balances at Dec. 31, 2017	$ 187,900	$ 856	$ 682,809	$ (495,479)	$ (286)
Beginning Balances, shares at Dec. 31, 2017		85,598,534
Cumulative-effect adjustment | Topic 606 [Member]	1,117			1,117
Issuance of common stock upon exercise of stock options and in connection with restricted stock units, net of tax	10,584	$ 14	10,570
Issuance of common stock upon exercise of stock options and in connection with restricted stock units, net of tax, shares		1,442,674
Stock-based compensation	3,050		3,050
Net unrealized gain (loss) on marketable securities	(99)				(99)
Net loss	(20,187)			(20,187)
Ending Balances at Mar. 31, 2018	182,365	$ 870	696,429	(514,549)	(385)
Ending Balances, shares at Mar. 31, 2018		87,041,208
Beginning Balances at Dec. 31, 2018	367,257	$ 1,022	929,632	(562,696)	(1,440)	$ 739
Beginning Balances, shares at Dec. 31, 2018		102,187,471
Cumulative-effect adjustment | Topic 842 [Member]	897			897
Issuance of common stock upon exercise of stock options and in connection with restricted stock units, net of tax	216	$ 1	215
Issuance of common stock upon exercise of stock options and in connection with restricted stock units, net of tax, shares		141,281
Issuance costs related to public offering	(258)		(258)
Stock-based compensation	4,523		4,523
Foreign currency translation adjustment	(1,504)				(1,504)
Net unrealized gain (loss) on marketable securities	253				253
Net loss	(42,203)			(42,150)		(53)
Ending Balances at Mar. 31, 2019	$ 329,181	$ 1,023	$ 934,112	$ (603,949)	$ (2,691)	$ 686
Ending Balances, shares at Mar. 31, 2019		102,328,752