INVESTMENTS (Tables)

9 Months Ended

Sep. 30, 2021

INVESTMENTS

Summary of investments in available-for-sale

									Continuous		Continuous
			Gross		Gross				Unrealized		Unrealized
			Unrealized		Unrealized				Loss Position		Loss Position
	Amortized		Holding		Holding		Fair		less than 12		greater than 12
September 30, 2021	Cost		Gains		Losses		Value		Months		Months
Available-for-sale
Short-term:
Commercial paper	$	292,094	$	—	$	—	$	292,094	$	—	$	—
Certificates of deposit		47,616		—		—		47,616		—		—
U.S. government agency securities		70,202		10		2		70,210		2		—
U.S. treasuries		814,178		30		62		814,146		62		—
Long-term:
U.S. government agency securities		1,416		—		—		1,416		—		—
U.S. treasuries		26,840		1		2		26,839		2		—
Total	$	1,252,346	$	41	$	66	$	1,252,321	$	66	$	—

									Continuous		Continuous
			Gross		Gross				Unrealized		Unrealized
			Unrealized		Unrealized				Loss Position		Loss Position
	Amortized		Holding		Holding		Fair		less than 12		greater than 12
December 31, 2020	Cost		Gains		Losses		Value		Months		Months
Available-for-sale
Short-term:
Commercial paper	$	119,886	$	—	$	—	$	119,886	$	—	$	—
Certificates of deposit		20,387		—		—		20,387		—		—
Municipal securities		9,083		—		—		9,083		—		—
U.S. government agency securities		81,521		13		3		81,531		3		—
U.S. treasuries		650,386		150		69		650,467		69		—
Long-term:
U.S. government agency securities		10,350		1		—		10,351		—		—
U.S. treasuries		33,946		1		7		33,940		7		—
Total	$	925,559	$	165	$	79	$	925,645	$	79	$	—

Summary of the underlying contractual maturities of investments

	September 30, 2021				December 31, 2020
	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Less than 1 year:
Commercial paper	$	292,094	$	292,094	$	119,886	$	119,886
Municipal securities		—		—		9,083		9,083
U.S. government agency securities		70,202		70,210		81,521		81,531
Certificates of deposit		47,616		47,616		20,387		20,387
U.S. treasuries		814,178		814,146		650,386		650,467
Due 1 - 10 years:
U.S. treasuries		26,840		26,839		33,946		33,940
U.S. government agency securities		1,416		1,416		10,350		10,351
Total	$	1,252,346	$	1,252,321	$	925,559	$	925,645