Cash, cash equivalents and investments - Cash Equivalents and Investments (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2020 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	$ 32,881
Unrealized gains	72
Unrealized losses	(41)
Fair Value	32,912
U.S. treasuries
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	11,944
Unrealized gains	49
Unrealized losses	0
Fair Value	$ 11,993
U.S. treasuries | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contractual maturity	44 days
U.S. treasuries | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contractual maturity	170 days
Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contractual maturity	77 days
Amortized Cost	$ 1,567
Unrealized gains	3
Unrealized losses	(1)
Fair Value	1,569
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	19,370
Unrealized gains	20
Unrealized losses	(40)
Fair Value	$ 19,350
Corporate bonds | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contractual maturity	22 days
Corporate bonds | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contractual maturity	132 days