Fair Value of Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2019

Fair Value of Financial Instruments

Summary of financial assets and liabilities subject to fair value measurements on a recurring basis

	December 31, 2019
	Level 1		Level 2		Level 3		Total
Assets
Money market funds	$	152,770	$	—	$	—	$	152,770
Certificates of deposit		1,950		—		—		1,950
Corporate debt securities		—		3,459		—		3,459
U.S. Treasury securities		20,052		—		—		20,052
	$	174,772	$	3,459	$	—	$	178,231
	December 31, 2018
	Level 1		Level 2		Level 3		Total
Assets
Money market funds	$	109,630	$	—	$	—	$	109,630
Total	$	109,630	$	—	$	—	$	109,630
Liabilities
Warrant liability	$	—	$	—	$	380	$	380
Total	$	—	$	—	$	380	$	380

Summary of fair value of the warrants were calculated using the Black-Scholes option pricing model

	December 31,
	2018
Exercise price (1)	$	14.46
Stock price (2)	$	13.20
Time to maturity (in years)		3.64
Volatility (3)		83.7	%
Risk-free interest rate (4)		2.50	%
Expected dividend	$	—

(1) Based upon terms provided in the warrant agreement.

(2) Based upon an independently prepared valuation as of December 31, 2018, adjusted for the one-for-six reverse stock split.  

(3) Based upon the historical daily volatility of a group of peer public company closing prices.

(4) Based upon interest rate for U.S. Treasury Bonds, as published by the U.S. Federal Reserve.