Fair value measurements (Tables)

9 Months Ended

Sep. 30, 2019

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 September 30, 2019 and December 31, 2018 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)
September 30, 2019	(in thousands)
Money market funds included in cash and cash equivalents	$	81,711	$	81,711	$	—	$	—
Marketable securities:
U.S. Treasury notes		224,760		224,760		—		—
Equity securities		2,024		2,024		—		—
Total marketable securities	$	226,784	$	226,784	$	—	$	—
Warrants to purchase equity securities		648		—		648		—
Total	$	309,143	$	308,495	$	648	$	—
December 31, 2018
Money market funds included in cash and cash equivalents	$	46,173	$	46,173	$	—	$	—
Marketable securities:
U.S. Treasury notes		108,947		108,947		—		—
Equity securities		628		628		—		—
Total marketable securities	$	109,575	$	109,575	$	—	$	—
Warrants to purchase equity securities		234		—		234		—
Total	$	155,982	$	155,748	$	234	$	—

Schedule of fair value assumptions

The assumptions utilized to value the warrants to purchase equity securities as of September 30, 2019 and December 31, 2018 are as follows:

	As of September 30,		As of December 31,
	2019		2018
Risk-free interest rate	1.6	%	2.5	%
Expected dividend yield	—	%	—	%
Expected term (in years)	1.9		2.7
Expected volatility	70.1	%	112.7	%