Summary of Company Cash, Cash Equivalents and Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents, Amortized cost	$ 835,044	$ 370,827
Cash and cash equivalents, Gross unrealized gains	36	3
Cash and cash equivalents, Gross unrealized losses		(1)
Cash and cash equivalents	835,080	370,829	$ 599,691
Cash, cash equivalents and investments, Amortized cost	1,124,679	1,174,011
Cash, cash equivalents and investments, Gross unrealized gains	71	12
Cash, cash equivalents and investments, Gross unrealized losses	(2)	(111)
Cash, cash equivalents and investments, Fair market value	1,124,748	1,173,912
Available for sale debt securities current, Amortized cost	289,635	803,184
Available for sale debt securities current, Gross unrealized gains	35	9
Available for sale debt securities current, Gross unrealized losses	(2)	(110)
Available for sale debt securities current, Fair market value	289,668	803,083
Cash and Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents, Amortized cost	315,589	244,302
Cash and cash equivalents	315,589	244,302
Commercial Paper [Member]
Cash and Cash Equivalents [Line Items]
Available for sale debt securities, Amortized cost		125,907
Available for sale debt securities, Fair market value		125,907
Government and Government Agency Bonds [Member]
Cash and Cash Equivalents [Line Items]
Available for sale debt securities, Amortized cost	809,090	760,258
Available for sale debt securities, Gross unrealized gains	71	12
Available for sale debt securities, Gross unrealized losses	(2)	(35)
Available for sale debt securities, Fair market value	$ 809,159	760,235
Corporate Bonds [Member]
Cash and Cash Equivalents [Line Items]
Available for sale debt securities, Amortized cost		43,544
Available for sale debt securities, Gross unrealized losses		(76)
Available for sale debt securities, Fair market value		$ 43,468

Available for sale debt securities current accumulated gross unrealized gain before tax.

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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