Fair Value Measurements Rollforward (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Issues	$ 2,176,000
Change in fair value of warrant liability	(387,000)	$ 78,000
Balance at March 31, 2018	2,608,000
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in fair value of warrant liability	(387,000)
Balance at March 31, 2018	$ 2,608,000