CASH, CASH EQUIVALENTS, AND INVESTMENTS - Amortized Cost (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 1,557,815	$ 1,412,665	$ 458,058
Total cost basis	1,757,958	1,460,260
Unrealized Gains	0	48
Unrealized Losses	0	(6)
Total fair value	1,757,958	1,460,302
Cash and Cash Equivalents	1,557,815	1,412,665
Marketable Securities	200,143	47,637
Time deposit
Cash and Cash Equivalents [Line Items]
Cost Basis	300,000
Unrealized Gains	0
Unrealized Losses	0
Fair Value	300,000
Cash and Cash Equivalents	300,000
Marketable Securities	0
Mutual fund
Cash and Cash Equivalents [Line Items]
Cost Basis	200,143
Unrealized Gains	0
Unrealized Losses	0
Fair Value	200,143
Cash and Cash Equivalents	0
Marketable Securities	200,143
Commercial paper
Cash and Cash Equivalents [Line Items]
Cost Basis		81,037
Unrealized Gains		1
Unrealized Losses		0
Fair Value		81,038
Cash and Cash Equivalents		81,038
Corporate debt securities
Cash and Cash Equivalents [Line Items]
Cost Basis		29,891
Unrealized Gains		26
Unrealized Losses		(2)
Fair Value		29,915
Cash and Cash Equivalents		3,506
Marketable Securities		26,409
Asset-backed securities
Cash and Cash Equivalents [Line Items]
Cost Basis		12,518
Unrealized Gains		19
Unrealized Losses		(4)
Fair Value		12,533
Cash and Cash Equivalents		0
Marketable Securities		12,533
U.S. agency securities
Cash and Cash Equivalents [Line Items]
Cost Basis		6,993
Unrealized Gains		2
Unrealized Losses		0
Fair Value		6,995
Cash and Cash Equivalents		0
Marketable Securities		6,995
U.S. Treasury securities
Cash and Cash Equivalents [Line Items]
Cost Basis		1,700
Unrealized Gains		0
Unrealized Losses		0
Fair Value		1,700
Cash and Cash Equivalents		0
Marketable Securities		1,700
Cash
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	60,674	709,924
Money market funds
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 1,197,141	$ 618,197