Stock Purchase Warrants (Details Textual) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended			3 Months Ended
	Nov. 18, 2016	Oct. 10, 2014	Oct. 25, 2012	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Equity, Class of Treasury Stock [Line Items]
Change in fair value of warrant liabilities				$ (5,090)	$ 498
Warrant liabilities				$ 9,731		$ 14,821
Warrant [Member]
Equity, Class of Treasury Stock [Line Items]
Issuance Of Warrants To Purchase Of Common Stock			635,855
Warrants Exercise Price Per Share			$ 1.60
Class of Warrant or Right, Outstanding				311,834
Stock Warrants [Member]
Equity, Class of Treasury Stock [Line Items]
Sale of Stock, Price Per Share		$ 1.47
Change in fair value of warrant liabilities		$ 7,400		$ 1,000
Proceeds from Issuance of Common Stock		$ 19,100
Sale of Stock, Number of Shares Issued in Transaction		14,059,616
Issuance Of Warrants To Purchase Of Common Stock		0.5			500,000
Share-Based Compensation Arrangement By Share-Based Payment Award, Options, Exercisable, Number		7,029,808
Share Based Compensation Arrangement By Share Based Payment Award Warrants Vested and Expected To Vest Outstanding Number		1.75
Warrant liabilities				1,100	$ 11,100
IPO [Member]
Equity, Class of Treasury Stock [Line Items]
Sale of Stock, Price Per Share	$ 1.00
Stock Issued During Period, Shares, New Issues	25,000,000
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	50,000,000
Warrants Not Settleable in Cash, Fair Value Disclosure	$ 15,700			8,600
Change in fair value of warrant liabilities				$ 4,100
IPO [Member] | Series A [Member]
Equity, Class of Treasury Stock [Line Items]
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 1.43
IPO [Member] | Series B [Member]
Equity, Class of Treasury Stock [Line Items]
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 1.72
Investment Warrants Expiration Date1	Dec. 31, 2017