Financial Instruments and Fair Value Measurements

3 Months Ended

Mar. 31, 2019

Fair Value Disclosures [Abstract]

Financial Instruments and Fair Value Measurements

3. Financial Instruments and Fair Value Measurements

The following tables summarize the Company’s financial assets and liabilities measured at fair value on a recurring basis by level within the fair value hierarchy:

	March 31, 2019
	Level 1		Level 2		Level 3		Total
	(in thousands)
Assets:
Money market funds	$	111,801	$	—	$	—	$	111,801
Total assets	$	111,801	$	—	$	—	$	111,801

	December 31, 2018
	Level 1		Level 2		Level 3		Total
	(in thousands)
Assets:
Money market funds	$	21,680	$	—	$	—	$	21,680
Total assets	$	21,680	$	—	$	—	$	21,680
Liabilities:
Convertible preferred stock warrant liability	$	—	$	—	$	313	$	313
Total liabilities	$	—	$	—	$	313	$	313

There were no transfers between Levels 1, 2 or 3 for the periods presented.

The change in the fair value of the warrant liability for the three months ended March 31, 2019 is summarized below (in thousands):

Balance at December 31, 2018	$	313
Change in fair value of warrant liability		609
Net exercise of warrants		(133	)
Conversion of Series A preferred stock warrants to common    stock warrants upon the closing of the IPO		(789	)
Balance at March 31, 2019	$	—

The change in the fair value of the warrant liability for the three months ended March 31, 2018 is summarized below (in thousands):

Balance at December 31, 2017	$	577
Exercise of warrants		(211	)
Expiration of warrants, included in change in fair value of   warrant liability		(87	)
Change in fair value of warrant liability		46
Balance at March 31, 2018	$	325

The valuation of the Company’s convertible preferred stock warrant liability contains unobservable inputs that reflect the Company’s own assumptions for which there is little, if any, market activity for at the measurement date. Accordingly, the Company’s convertible preferred stock warrant liability is measured at fair value on a recurring basis using unobservable inputs and are classified as Level 3 inputs, and any change in fair value is recognized as change in fair value of warrant liability in the condensed consolidated statements of operations and comprehensive loss.

The fair value of the warrants was determined using the Black-Scholes option pricing model and the following assumptions:

	Three Months Ended March 31,
	2019		2018
Expected term (in years)		5.28	6.21
Expected volatility	43.9%		42.8%
Risk-free interest rate	2.49%		2.62%
Expected dividend yield	0%		0%