Redeemable Preferred Stock (Details)				1 Months Ended	12 Months Ended
	Dec. 22, 2016 $ / shares shares	Aug. 26, 2014 $ / shares shares	May 08, 2013 USD ($) item shares	Dec. 31, 2016 USD ($) item $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) shares	Dec. 31, 2013 shares	Dec. 31, 2015 $ / shares shares	May 16, 2013 shares
Redeemable preferred stock
Shares of common stock that can be purchased from warrants issued in an underwritten public offering (in shares)				3,120,000	3,120,000
Net proceeds from public offering | $				$ 11,900,000	$ 27,500,000	$ 165,700,000
Proceeds from Issuance of Warrants | $						$ 11,800,000
Weighted average exercise price of warrants (in dollars per share) | $ / shares				$ 1.50	$ 1.50
Common Stock
Redeemable preferred stock
Shares issued upon conversion of redeemable stock (in shares)						5,521,676
Series C Redeemable Convertible Preferred Stock
Redeemable preferred stock
Redeemable stock issued (in shares)				5,231	5,231			5,231	10,431
Redeemable stock issued, stated value (in dollars per share) | $ / shares				$ 0.01	$ 0.01			$ 0.01
Shares issued upon conversion of redeemable stock (in shares)							5,200
Redeemable convertible Preferred Stock, shares outstanding				5,231	5,231			5,231
Series C Redeemable Convertible Preferred Stock | Air Liquide
Redeemable preferred stock
Redeemable stock issued (in shares)			10,431	5,231	5,231
Number of directors entitled to designate on board under Securities Purchase Agreement | item			1
Dividend rate					8.00%
Aggregate purchase price of shares issued | $			$ 2,595,400
Conversion price per share | $ / shares		$ 0.2343
Shares issued upon conversion of redeemable stock (in shares)		(5,200)
Adjusted conversion price per share | $ / shares				$ 0.2343	$ 0.2343			$ 0.2343
Series C Redeemable Convertible Preferred Stock | Air Liquide | Common Stock
Redeemable preferred stock
Shares issued upon conversion of redeemable stock (in shares)		5,521,676
Series D Redeemable Convertible Preferred Stock
Redeemable preferred stock
Redeemable stock issued (in shares)	18,500			18,500	18,500			0
Redeemable stock issued, par value (in dollars per share) | $				$ 0.01	$ 0.01
Redeemable stock issued, stated value (in dollars per share) | $ / shares	$ 1,000			$ 0.01	$ 0.01			$ 0.01
Net proceeds from public offering | $				$ 15,600,000
Preferred stock, number of monthly redemption installments. | item				10
Preferred stock redemption, monthly installment amount | $				$ 1,900,000
Conversion discount, percent of market value	12.00%
Conversion price per share (in dollars per share) | $ / shares	$ 1.55
Shares issued upon conversion of redeemable stock (in shares)					0
Redeemable convertible Preferred Stock, shares outstanding				18,500	18,500
Underwriters agreement
Redeemable preferred stock
Shares of common stock that can be purchased from warrants issued in an underwritten public offering (in shares)				7,381,500	7,381,500