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, 2020	Dec. 31, 2019
Cash and Cash Equivalents, at Carrying Value [Abstract]
Cash and cash equivalents	$ 2,045,474	$ 1,141,263
Short-term investments:
Gross Unrealized Gains	2,088	526
Gross Unrealized Losses	(10)	(120)
Restricted cash	33,620	89,646
Cash, cash equivalents, short-term investments, and restricted cash, amortized cost	3,568,183	2,511,492
Cash, cash equivalents, short-term investments, and restricted cash, estimated fair market value	3,570,261	2,511,898
U.S. government agency securities
Short-term investments:
Amortized Cost	463,806	861,862
Gross Unrealized Gains	1,909	365
Gross Unrealized Losses	0	(73)
Estimated Fair Market Value	465,715	862,154
Corporate notes and bonds
Short-term investments:
Amortized Cost	30,094	159,382
Gross Unrealized Gains	119	91
Gross Unrealized Losses	0	(42)
Estimated Fair Market Value	30,213	159,431
Commercial paper
Short-term investments:
Amortized Cost	14,972	150,267
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	14,972	150,267
Treasury bills
Short-term investments:
Amortized Cost	963,200	79,989
Gross Unrealized Gains	41	14
Gross Unrealized Losses	(10)	0
Estimated Fair Market Value	963,231	80,003
Municipal securities
Short-term investments:
Amortized Cost	16,519	27,836
Gross Unrealized Gains	19	56
Gross Unrealized Losses	0	(3)
Estimated Fair Market Value	16,538	27,889
Certificates of deposit
Short-term investments:
Amortized Cost	498	1,245
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	498	1,245
Cash
Cash and Cash Equivalents, at Carrying Value [Abstract]
Cash and cash equivalents	190,389	194,955
Money market funds
Cash and Cash Equivalents, at Carrying Value [Abstract]
Cash and cash equivalents	1,784,896	872,431
U.S. government agency securities
Cash and Cash Equivalents, at Carrying Value [Abstract]
Cash and cash equivalents, at cost		35,011
Cash and cash equivalents, gross unrealized losses		(2)
Cash and cash equivalents		35,009
Commercial paper
Cash and Cash Equivalents, at Carrying Value [Abstract]
Cash and cash equivalents		31,113
Treasury bills
Cash and Cash Equivalents, at Carrying Value [Abstract]
Cash and cash equivalents	$ 70,189	6,441
Corporate notes and bonds
Cash and Cash Equivalents, at Carrying Value [Abstract]
Cash and cash equivalents		1,065
Certificates of deposit
Cash and Cash Equivalents, at Carrying Value [Abstract]
Cash and cash equivalents		$ 249