Redeemable Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended	6 Months Ended
	Apr. 05, 2017	Jan. 26, 2017	Dec. 31, 2016	Jun. 30, 2017
Redeemable preferred stock
Common Stock, par value (in dollars per share)			$ 0.01	$ 0.01
Payments for redemption of preferred stock				$ 3,700
Series C Redeemable Convertible Preferred Stock
Redeemable preferred stock
Redeemable stock issued, stated value (in dollars per share)		$ 0.01	$ 0.01	$ 0.01
Shares sold by shareholders (in shares)		2,620
Redeemable convertible Preferred Stock, shares outstanding			5,231	5,231
Series C Redeemable Convertible Preferred Stock | Air Liquide
Redeemable preferred stock
Redeemable convertible Preferred Stock, shares outstanding		2,611
Series C Redeemable Convertible Preferred Stock | FiveT Capital Holding AG
Redeemable preferred stock
Redeemable convertible Preferred Stock, shares outstanding		1,750
Series C Redeemable Convertible Preferred Stock | FiveMore Special Situations Fund Limited
Redeemable preferred stock
Redeemable convertible Preferred Stock, shares outstanding		870
Series D Redeemable Convertible Preferred Stock
Redeemable preferred stock
Shares issued (in shares)			18,500
Redeemable stock issued, stated value (in dollars per share)			$ 0.01	$ 0.01
Shares of common stock that can be purchased from warrants issued			7,381,500
Net proceeds from public offering			$ 15,600
Shares redeemed (in shares)				3,700
Payments for redemption of preferred stock				$ 3,700
Conversion price per share	$ 1.55
Shares issued upon conversion of redeemable stock (in shares)	9,548,393
Redeemable convertible Preferred Stock, shares outstanding	0		18,500	0