Stock Purchase Warrants (Details Textual) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended			3 Months Ended		6 Months Ended
	Nov. 18, 2016	Oct. 10, 2014	Oct. 25, 2012	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	Mar. 31, 2016
Equity, Class of Treasury Stock [Line Items]
Change in fair value of warrant liability				$ (2,159)	$ (3,513)	$ (7,249)	$ (3,015)
Warrant liabilities				$ 7,573		$ 7,573		$ 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		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 liability		$ 7,400		$ 200	$ 3,500	$ 1,100	$ 3,000
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
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				1,000		1,000			$ 7,600
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			6,600		6,600
Change in fair value of warrant liability				$ 2,000		$ 6,100
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