Fair value measurements - Investments (Details) $ in Thousands	Sep. 30, 2022 USD ($)
Fair value
Total investment securities	$ 151,583
Commercial paper
Fair value
Total investment securities	51,219
Corporate notes / bonds
Fair value
Total investment securities	38,703
Debt security
Fair value
Total investment securities	1,000
Money market funds
Fair value
Total investment securities	2,020
U.S. govt. agencies
Fair value
Total investment securities	33,944
U.S. treasuries
Fair value
Total investment securities	24,697
Recurring
Fair value
Total investment securities	151,583
Recurring | Commercial paper
Fair value
Total investment securities	51,219
Recurring | Corporate notes / bonds
Fair value
Total investment securities	38,703
Recurring | Debt security
Fair value
Total investment securities	1,000
Recurring | Money market funds
Fair value
Total investment securities	2,020
Recurring | U.S. govt. agencies
Fair value
Total investment securities	33,944
Recurring | U.S. treasuries
Fair value
Total investment securities	24,697
Recurring | Level 1
Fair value
Total investment securities	60,661
Recurring | Level 1 | Money market funds
Fair value
Total investment securities	2,020
Recurring | Level 1 | U.S. govt. agencies
Fair value
Total investment securities	33,944
Recurring | Level 1 | U.S. treasuries
Fair value
Total investment securities	24,697
Recurring | Level 2
Fair value
Total investment securities	89,922
Recurring | Level 2 | Commercial paper
Fair value
Total investment securities	51,219
Recurring | Level 2 | Corporate notes / bonds
Fair value
Total investment securities	38,703
Recurring | Level 3
Fair value
Total investment securities	1,000
Recurring | Level 3 | Debt security
Fair value
Total investment securities	$ 1,000