Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) - Fair Value, Measurements, Recurring $ in Thousands	Dec. 31, 2020 USD ($)
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Money market instruments	$ 2,464
Corporate bonds	0
Treasury bills
Asset-backed securities	0
Agency bonds	0
Sovereign bonds	0
Municipal bonds	0
Economic hedge forward contracts	0
Liabilities:
Economic hedge forward contracts	0
Significant Other Observable Inputs (Level 2)
Assets:
Money market instruments	0
Corporate bonds	236,142
Treasury bills	131,861
Asset-backed securities	92,218
Agency bonds	19,006
Sovereign bonds	12,100
Municipal bonds	7,038
Economic hedge forward contracts	265
Liabilities:
Economic hedge forward contracts	38
Unobservable Inputs (Level 3)
Assets:
Money market instruments	0
Corporate bonds	0
Treasury bills
Asset-backed securities	0
Agency bonds	0
Sovereign bonds	0
Municipal bonds
Economic hedge forward contracts	0
Liabilities:
Economic hedge forward contracts	$ 0