Fair value measurements (Details) - Recurring - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair value measurements
Assets measured at fair value	$ 120,769	$ 98,343
Money market funds, included in cash and cash equivalents
Fair value measurements
Money market funds	120,424	97,998
Money market funds, included in restricted cash
Fair value measurements
Money market funds	179	179
Money market funds, included in other assets
Fair value measurements
Money market funds	166	166
Level 1
Fair value measurements
Assets measured at fair value	120,769	98,343
Level 1 | Money market funds, included in cash and cash equivalents
Fair value measurements
Money market funds	120,424	97,998
Level 1 | Money market funds, included in restricted cash
Fair value measurements
Money market funds	179	179
Level 1 | Money market funds, included in other assets
Fair value measurements
Money market funds	$ 166	$ 166