Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2019

Fair Value Measurements

Assumptions used to calculate common stock warrants

	Three months ended
	March 31, 2019	March 31, 2018
Risk-free interest rate	2.51%	1.64% - 2.28%
Volatility	74.93%	18.40% - 81.95%
Expected average term	0.53	0.01 - 1.53

Schedule of activity in the common stock warrant liability

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

	Three months ended
	March 31, 2019		March 31, 2018
Beginning of period	$	105	$	4,391
Change in fair value of common stock warrants		2,126		(1,258)
End of period	$	2,231	$	3,133

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

	Three months ended
	March 31, 2019	March 31, 2018
Risk-free interest rate	2.32% - 2.33%	2.72% - 2.73%
Volatility	85.00%	85.00%
Expected average term	8.01-  8.30	9.01 - 9.30

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 March 2019 - second tranche		2.05		1.94
As of March 2018 - second tranche		1.57		1.71