Marketable securities (Tables)

9 Months Ended

Sep. 30, 2019

Marketable securities

Schedule of reconciliation of marketable securities from cost basis to fair value

			Gross		Gross
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value
September 30, 2019
Commercial paper	$	14,871	$	—	$	—	$	14,871
Corporate bonds		11,984		26		—		12,010
U.S. Treasuries		26,923		2		—		26,925
	$	53,778	$	28	$	—	$	53,806

			Gross		Gross
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value
December 31, 2018
U.S. Treasuries	$	10,505	$	—	$	(8)	$	10,497
	$	10,505	$	—	$	(8)	$	10,497