Investments - Narrative (Detail)	12 Months Ended
	Dec. 31, 2019 USD ($) security	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contractual maturities term (maximum)	36 months
Number of available-for-sale securities in unrealized loss position | security	91
Other-than-temporary impairments considered	$ 0
Unrealized gain recognized on sale of marketable equity securities			$ 10,700,000
Tax effect recognized on sale of marketable equity securities			$ 3,500,000
Debt and equity investments in privately-held companies included in other assets	22,400,000	$ 14,600,000
Marketable equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Proceeds from sale of marketable equity securities		40,000,000.0
Realized gain recognized on sale of marketable equity securities		19,300,000
Marketable securities	$ 0	$ 0