Fair Value Measurement - Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Assets:
Investments	$ 234,178	$ 150,359
Total	466,078	422,709
Deposits held with banks
Assets:
Cash and cash equivalents:	214,702	130,807
Short-term highly liquid investments
Assets:
Cash and cash equivalents:	17,198	141,543
Level 1
Assets:
Investments	206,724	69,746
Total	438,624	342,096
Level 1 | Deposits held with banks
Assets:
Cash and cash equivalents:	214,702	130,807
Level 1 | Short-term highly liquid investments
Assets:
Cash and cash equivalents:	17,198	141,543
Level 2
Assets:
Investments	27,454	80,613
Total	27,454	80,613
Level 2 | Deposits held with banks
Assets:
Cash and cash equivalents:	0	0
Level 2 | Short-term highly liquid investments
Assets:
Cash and cash equivalents:	0	0
Level 3
Assets:
Investments		0
Total	0	0
Level 3 | Deposits held with banks
Assets:
Cash and cash equivalents:	0	0
Level 3 | Short-term highly liquid investments
Assets:
Cash and cash equivalents:	$ 0	$ 0