Convertible Notes - Convertible Promissory Notes Outstanding (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Sep. 30, 2016
Debt Instrument [Line Items]
Debt discount	$ (18,003)	$ (18,003)
Warrants Issued With September 2016 Convertible Notes
Debt Instrument [Line Items]
Debt discount	(9,598)	(9,598)		$ (9,600)
Compounded Bifurcated Derivatives
Debt Instrument [Line Items]
Debt discount	(1,267)	(1,267)		(1,300)
Beneficial Conversion Feature
Debt Instrument [Line Items]
Debt discount	(7,138)	(7,138)		(7,200)
Convertible Debt
Debt Instrument [Line Items]
Convertible promissory notes	18,003	18,003	$ 50
Debt discount				$ (18,100)
Convertible promissory notes, net	$ 0	$ 0