Cash, cash equivalents and short-term investments - Summary of cost and estimated fair value of short-term investments (Details) $ in Thousands	Sep. 30, 2020 USD ($)
Amortized Cost
Due within one year	$ 29,750
Due between one and two years	28,791
Due between two and three years	10,709
Amortized Cost	69,250
Estimated Fair Value
Due within one year	30,096
Due between one and two years	29,479
Due between two and three years	10,930
Total	$ 70,505