Fair value of financial instruments (Tables)

3 Months Ended

Mar. 31, 2020

Cash and Cash Equivalents [Abstract]

Schedule of Stockholders' Equity Note, Warrants or Rights

As of March 31, 2020, the Company had the following potentially issuable shares of common stock related to unexercised warrants outstanding:

	Shares	Exercise price		Expiration date	Classification
Hercules Warrant	41,177	$	6.80	Q2 2023	Equity
2018 Public Offering Warrants	3,616,944	$	9.60	Q1 2023	Liability
Private Placement Warrants	932,812	$	4.52	Q1 2024	Equity
Pre-Funded Warrants	531,250	$	0.08	Q1 2039	Equity
	5,122,183

Schedule of financial instruments measured at fair value on recurring basis

			Quoted prices in active markets		Significant other observable inputs		Significant unobservable inputs
	Total		(Level 1)		(Level 2)		(Level 3)
March 31, 2020
Assets:
Cash equivalents	$	25,985	$	25,985	$	—	$	—
Total assets	$	25,985	$	25,985	$	—	$	—
Liabilities:
Warrant liability	$	1,705	$	—	$	—	$	1,705
Total liabilities	$	1,705	$	—	$	—	$	1,705
December 31, 2019
Assets:
Cash equivalents	$	39,971	$	39,971	$	—	$	—
Total assets	$	39,971	$	39,971	$	—	$	—
Liabilities:
Warrant liability	$	2,486	$	—	$	—	$	2,486
Total liabilities	$	2,486	$	—	$	—	$	2,486

Fair Value Measurement Inputs and Valuation Techniques

The following table details the assumptions used in the Monte Carlo simulation models used to estimate the fair value of the Warrant Liability as of March 31, 2020 and December 31, 2019, respectively:

	March 31, 2020			December 31, 2019
Stock price	$	1.72		$	2.07
Volatility	50.0% - 124.5%			50.0% - 116.6%
Remaining term (years)	2.8			3.1
Expected dividend yield	—			—
Risk-free rate	0.3		%	1.6		%
Annual acquisition event probability	30.0		%	20.0		%

Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation

The following table reflects the change in the Company’s Level 3 warrant liability (in thousands):

	Warrant Liability
Balance at December 31, 2019	$	2,486
Change in fair value	(781		)
Balance at March 31, 2020	$	1,705