Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2019

Fair Value Disclosures [Abstract]

Summary of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis

The following table sets forth the fair value of financial assets and liabilities that were measured at fair value on a recurring basis (in thousands):

	June 30, 2019
	Level 1		Level 2		Level 3		Total
	(unaudited)
Financial assets
Money market funds	$	35,695	$	—	$	—	$	35,695
Commercial paper		—		88,161		—		88,161
U.S. government debt and agency securities		—		273,713		—		273,713
Corporate bonds		—		22,661		—		22,661
Total financial assets	$	35,695	$	384,535	$	—	$	420,230
Financial liabilities
Convertible preferred stock warrant liability	$	—	$	—	$	2,602	$	2,602
Total financial liabilities	$	—	$	—	$	2,602	$	2,602

	December 31, 2018
	Level 1		Level 2		Level 3		Total
Financial assets
Money market funds	$	45,998	$	—	$	—	$	45,998
Commercial paper		—		16,887		—		16,887
U.S. government debt and agency securities		—		85,623		—		85,623
Corporate bonds		—		7,478		—		7,478
Total financial assets	$	45,998	$	109,988	$	—	$	155,986
Financial liabilities
Convertible preferred stock warrant liability	$	—	$	—	$	336	$	336
Total financial liabilities	$	—	$	—	$	336	$	336

Summary of Fair Value of Convertible Preferred Stock Warrant Liability Estimated Using Black-Scholes Option Pricing Model

The fair value of the convertible preferred stock warrant liability is estimated using the Black-Scholes option-pricing model. Certain inputs were utilized in the option-pricing model as follows:

	June 30, 2019			December 31, 2018
	(unaudited)
Fair value estimate	$	48.30		$	8.27
Expected term (in years)		1.81			2.31
Risk-free interest rate		1.8	%		2.5	%
Expected volatility		61.1	%		55.3	%
Expected dividend yield		—			—