Fair Value Measurements (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Fair value measurements by level for assets and liabilities measured at fair value on a recurring basis [Abstract]
Increase in fair value of warrant liabilities	$ 2,800
Recurring [Member]
Fair value measurements by level for assets and liabilities measured at fair value on a recurring basis [Abstract]
Cash equivalents	53,485	$ 56,276
Warrant liabilities	(6,567)	(3,789)
Level I [Member] | Recurring [Member]
Fair value measurements by level for assets and liabilities measured at fair value on a recurring basis [Abstract]
Cash equivalents	53,485	56,276
Warrant liabilities	0	0
Level II [Member] | Recurring [Member]
Fair value measurements by level for assets and liabilities measured at fair value on a recurring basis [Abstract]
Cash equivalents	0	0
Warrant liabilities	0	0
Level III [Member] | Recurring [Member]
Fair value measurements by level for assets and liabilities measured at fair value on a recurring basis [Abstract]
Cash equivalents	0	0
Warrant liabilities	$ (6,567)	$ (3,789)