Fair Value Measurements - Reconciliation of Embedded Derivative Measured at Fair Value (Details) - Embedded Derivative Financial Instruments - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of warrant liability and embedded derivative
Balance at beginning of period	$ 0	$ 0
Transfers in and/or out of Level 3	0	0
Initial valuation of bifurcated derivative liability	0	3,936,000
Extinguishment of bifurcated derivative liability	0	(3,936,000)
Balance at end of period	$ 0	$ 0