Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) - Fair Value, Measurements, Recurring - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Liabilities:
Other than temporary impairment loss	$ 0	$ 0	$ 0
Other than temporary impairment loss non-current	0	$ 0	$ 0
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Money market instruments	15,933,000
Treasury bills	0
Corporate bonds	0
Asset-backed securities	0
Sovereign bonds	0
Municipal bonds	0
Agency bonds	0
Certificate of deposit	0
Economic hedge forward contracts
Liabilities:
Economic hedge forward contracts	0
Contingent consideration liabilities	0
Significant Other Observable Inputs (Level 2)
Assets:
Money market instruments	0
Treasury bills	309,248,000
Corporate bonds	212,098,000
Asset-backed securities	113,083,000
Sovereign bonds	22,299,000
Municipal bonds	6,952,000
Agency bonds	5,914,000
Certificate of deposit	4,328,000
Economic hedge forward contracts	857,000
Liabilities:
Economic hedge forward contracts	23,000
Contingent consideration liabilities	0
Unobservable Inputs (Level 3)
Liabilities:
Contingent consideration liabilities	$ 1,153,000