Warrants (Tables)

6 Months Ended

Jun. 30, 2018

Equity [Abstract]

Summary of Assumptions using Black- Scholes Option Pricing Model to estimate fair value

The fair value of the 2016 Placement Warrants of $6.8 million and $9.9 million at June 30, 2018 and December 31, 2017, respectively, was estimated using the Black-Scholes option pricing model and the following weighted-average assumptions:

	June 30, 2018		December 31, 2017
2016 Placement Warrant:
Expected term (in years)		5.2		5.7
Expected volatility	59.8%		62.1%
Risk-free interest rate	2.7%		2.2%
Expected dividend yield	0%		0%

The fair value of the 2017 Placement Warrants of $8.6 million and $12.5 million at June 30, 2018 and December 31, 2017, respectively, was estimated using the Black-Scholes option pricing model and the following weighted-average assumptions:

	June 30, 2018		December 31, 2017
2017 Placement Warrant:
Expected term (in years)		5.6		6.1
Expected volatility	60.0%		62.3%
Risk-free interest rate	2.8%		2.3%
Expected dividend yield	0%		0%