Summary of Company Cash, Cash Equivalents and Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents, Amortized cost	$ 1,502,639	$ 835,044
Cash and cash equivalents, Gross unrealized gains	9	36
Cash and cash equivalents	1,502,648	835,080	$ 370,829
Cash, cash equivalents and investments, Amortized cost	1,938,549	1,124,679
Cash, cash equivalents and investments, Gross unrealized gains	22	71
Cash, cash equivalents and investments, Gross unrealized losses		(2)
Cash, cash equivalents and investments, Fair market value	1,938,571	1,124,748
Available for sale debt securities current, Amortized cost	435,910	289,635
Available for sale debt securities current, Gross unrealized gains	13	35
Available for sale debt securities current, Gross unrealized losses		(2)
Available for sale debt securities current, Fair market value	435,923	289,668
Cash and Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents, Amortized cost	900,590	315,589
Cash and cash equivalents	900,590	315,589
Government and Government Agency Bonds [Member]
Cash and Cash Equivalents [Line Items]
Available for sale debt securities, Amortized cost	1,037,959	809,090
Available for sale debt securities, Gross unrealized gains	22	71
Available for sale debt securities, Gross unrealized losses		(2)
Available for sale debt securities, Fair market value	$ 1,037,981	$ 809,159

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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