Summary of Company Cash, Cash Equivalents and Short-term Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents, Amortized cost	$ 1,481,836	$ 1,502,639
Cash and cash equivalents, Gross unrealized gains		9
Cash and cash equivalents	1,481,836	1,502,648	$ 1,764,212
Cash, cash equivalents and investments, Amortized cost	1,737,817	1,938,549
Cash, cash equivalents and investments, Gross unrealized gains	16	22
Cash, cash equivalents and investments, Fair value	1,737,833	1,938,571
Available for sale debt securities current, Amortized cost	255,981	435,910
Available for sale debt securities current, Gross unrealized gains	16	13
Available for sale debt securities current, Fair value	255,997	435,923
Cash and Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents, Amortized cost	1,378,804	900,590
Cash and cash equivalents	1,378,804	900,590
Government and Government Agency Bonds [Member]
Cash and Cash Equivalents [Line Items]
Available for sale debt securities, Amortized cost	359,013	1,037,959
Available for sale debt securities, Gross unrealized gains	16	22
Available for sale debt securities, Fair value	$ 359,029	$ 1,037,981

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

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Cash and cash equivalents 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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Amortized cost of 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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