Summary of Company Cash, Cash Equivalents and Short-term Investments (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents, Amortized cost	$ 1,697,275	$ 1,502,639
Cash and cash equivalents, Gross unrealized gains		9
Cash and cash equivalents	1,697,275	1,502,648	$ 1,639,959
Cash, cash equivalents and investments, Amortized cost	1,727,275	1,938,549
Cash, cash equivalents and investments, Gross unrealized gains		22
Cash, cash equivalents and investments, Fair value	1,727,275	1,938,571
Available for sale debt securities current, Amortized cost	30,000	435,910
Available for sale debt securities current, Gross unrealized gains		13
Available for sale debt securities current, Fair value	30,000	435,923
Cash and Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents, Amortized cost	1,697,275	900,590
Cash and cash equivalents	1,697,275	900,590
Government and Government Agency Bonds [Member]
Cash and Cash Equivalents [Line Items]
Available for sale debt securities, Amortized cost	30,000	1,037,959
Available for sale debt securities, Gross unrealized gains		22
Available for sale debt securities, Fair value	$ 30,000	$ 1,037,981