Fair value measurements (Tables)

3 Months Ended

Mar. 31, 2020

Fair value measurements

Assets and liabilities measured at fair value on a recurring basis

Assets and liabilities measured at fair value on a recurring basis as of March 31, 2020 and December 31, 2019 are as follows:

			Quoted Prices		Significant
			in Active		Other		Significant
			Markets for		Observable		Unobservable
			Identical Assets		Inputs		Inputs
Assets	Total		(Level 1)		(Level 2)		(Level 3)
March 31, 2020	(in thousands)
Money market funds included in cash and cash equivalents	$	153,395	$	153,395	$	—	$	—
Marketable securities:
U.S. Treasury notes		85,704		85,704		—		—
Equity securities		1,432		1,432		—		—
Total marketable securities	$	87,136	$	87,136	$	—	$	—
Warrants to purchase equity securities		234		—		234		—
Total	$	240,765	$	240,531	$	234	$	—
December 31, 2019
Money market funds included in cash and cash equivalents	$	78,303	$	78,303	$	—	$	—
Marketable securities:
U.S. Treasury notes		195,491		195,491		—		—
Equity securities		1,920		1,920		—		—
Total marketable securities	$	197,411	$	197,411	$	—	$	—
Warrants to purchase equity securities		554		—		554		—
Total	$	276,268	$	275,714	$	554	$	—

Summary of fair value assumptions

	As of March 31,		As of December 31,
	2020		2019
Risk-free interest rate	0.2	%	1.6	%
Expected dividend yield	—	%	—	%
Expected term (in years)	1.4		1.7
Expected volatility	68.0	%	71.6	%