Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill and Intangible Asset Impairment		$ 469,000
Fair Value, Measurements, Recurring [Member]
Liabilities:
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net	$ 0	0	$ 0
Other Than Temporary Impairment Losses Investments Portion Recognized In Earnings Net, non current	0	$ 0	$ 0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Money market instruments	3,557,000
Corporate bonds	0
Treasury bills	0
Asset-backed securities	0
Sovereign bonds	0
Agency bonds	0
Municipal bonds	0
Economic hedge forward contracts
Liabilities:
Economic hedge forward contracts	0
Contingent consideration liabilities	0
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Money market instruments	0
Corporate bonds	300,437,000
Treasury bills	231,237,000
Asset-backed securities	132,038,000
Sovereign bonds	14,417,000
Agency bonds	5,921,000
Municipal bonds	5,337,000
Economic hedge forward contracts	1,000
Liabilities:
Economic hedge forward contracts	106,000
Contingent consideration liabilities	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Liabilities:
Contingent consideration liabilities	$ 2,544,000