Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2019

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis

The following table summarizes the financial instruments measured at fair value on a recurring basis in the consolidated balance sheets (in thousands) at December 31, 2018:

			Quoted Prices		Significant		Significant
			in Active		Other		Other
			Markets for		Observable		Unobservable
			IdenticalItems		Inputs		Inputs
	Total		(Level 1)		(Level 2)		(Level 3)
Common stock warrant liability	$	105	$	—	$	—	$	105

Schedule of activity in the common stock warrant liability

The following table shows the activity in the common stock warrant liability (in thousands):

	2019		2018
Beginning of period	$	105	$	4,391
Change in fair value of common stock warrants		(79)		(4,286)
Issuance of common stock warrants		—		—
Exercise of common stock warrants		(26)		—
End of period	$	—	$	105

Assumptions used to calculate common stock warrants

The Company used the following assumptions for its liability-classified common stock warrants for the year ended December 31, 2018:

Risk-free interest rate	1.64% - 2.66%
Volatility	18.40% - 81.69%
Expected average term	0.01 - 1.53

Schedule of fair value of warrants

		Amazon Warrant Shares		Walmart Warrant Shares
Issuance date - first tranche	$	1.15	$	1.88
As of vesting date - second tranche, first installment		2.16		—
As of vesting date - second tranche, second installment		1.54		—
As of December 2019 - second tranche		1.05		1.00
As of December 2018 - second tranche		0.98		0.92

Equity Instruments

Assumptions used to calculate common stock warrants

	Year ended
	January 1, 2019	December 31, 2018
Risk-free interest rate	2.60%-2.63%	2.60% - 3.02%
Volatility	0.95	75.00% - 85.00%
Expected average term	8.26-8.55	8.26 - 9.30