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Cash and Cash Equivalents, Short-term Investments and Restricted Cash - Amortized Cost, Gross Unrealized Gains and Losses, and Estimated Fair Market Value of Cash and Cash Equivalents and Available-for-Sale Investments (Detail) - USD ($)
$ in Thousands
Jun. 30, 2021
Dec. 31, 2020
Cash and Cash Equivalents, at Carrying Value [Abstract]    
Cash and cash equivalents $ 3,713,156 $ 1,703,130
Short-term investments:    
Gross Unrealized Gains 147 122
Gross Unrealized Losses 0 (59)
Restricted cash 141,024 75,805
Cash, cash equivalents, short-term investments, and restricted cash, amortized cost 4,734,908 3,996,980
Cash, cash equivalents, short-term investments, and restricted cash, estimated fair market value 4,735,055 3,997,043
U.S. government agency securities    
Short-term investments:    
Amortized Cost 829,791  
Gross Unrealized Gains 134  
Gross Unrealized Losses 0  
Estimated Fair Market Value 829,925 1,037,577
Treasury bills    
Short-term investments:    
Amortized Cost 44,975 1,163,748
Gross Unrealized Gains 13 65
Gross Unrealized Losses 0 0
Estimated Fair Market Value 44,988 1,163,813
U.S. government agency securities    
Short-term investments:    
Amortized Cost   1,037,572
Gross Unrealized Gains   57
Gross Unrealized Losses   (52)
Estimated Fair Market Value   1,037,577
Municipal securities    
Short-term investments:    
Amortized Cost 5,962 16,226
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 (6)
Estimated Fair Market Value 5,962 16,220
Certificates of deposit    
Short-term investments:    
Amortized Cost   498
Gross Unrealized Gains   0
Gross Unrealized Losses   0
Estimated Fair Market Value   498
Cash    
Cash and Cash Equivalents, at Carrying Value [Abstract]    
Cash and cash equivalents 218,514 213,518
Money market funds    
Cash and Cash Equivalents, at Carrying Value [Abstract]    
Cash and cash equivalents $ 3,494,642 1,486,384
Municipal securities    
Cash and Cash Equivalents, at Carrying Value [Abstract]    
Cash and cash equivalents, at cost   3,229
Cash and cash equivalents, gross unrealized losses   (1)
Cash and cash equivalents   $ 3,228