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INVESTMENTS (Tables)

6 Months Ended

Jun. 30, 2020

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
June 30, 2020		Cost			Gains			Losses			Value			Months			Months
Available-for-sale
Short-term:
Commercial paper		$	58,540		$	—		$	—		$	58,540		$	—		$	—
Certificates of deposit			3,624			—			—			3,624			—			—
U.S. government agency securities			44,851			41			9			44,883			9			—
U.S. treasuries			143,081			633			8			143,706			8			—
Long-term:
U.S. treasuries			2,077			—			—			2,077			—			—
Total		$	252,173		$	674		$	17		$	252,830		$	17		$	—


														Continuous			Continuous
					Gross			Gross						Unrealized			Unrealized
					Unrealized			Unrealized						Loss Position			Loss Position
		Amortized			Holding			Holding			Fair			less than 12			greater than 12
December 31, 2019		Cost			Gains			Losses			Value			Months			Months
Available-for-sale
Short-term:
Commercial paper		$	83,478		$	—		$	—		$	83,478		$	—		$	—
Certificates of deposit			28,049			—			—			28,049			—			—
Municipal securities			147,983			145			20			148,108			20			—
U.S. government agency securities			40,620			5			35			40,590			35			—
U.S. treasuries			211,055			134			31			211,158			31			—
Variable rate demand notes			21,680			—			—			21,680			—			—
Long-term:
Municipal securities			1,562			—			1			1,561			1			—
U.S. government agency securities			5,267						1			5,266			1			—
U.S. treasuries			6,077			1			—			6,078			—			—
Total		$	545,771		$	285		$	88		$	545,968		$	88		$	—

Summary of the underlying contractual maturities of investments


		June 30, 2020						December 31, 2019
		Amortized Cost			Fair Value			Amortized Cost			Fair Value
Less than 1 year:
Commercial paper		$	58,540		$	58,540		$	83,478		$	83,478
Municipal securities			—			—			147,983			148,108
U.S. government agency securities			44,851			44,883			40,620			40,590
Certificates of deposit			3,624			3,624			28,049			28,049
U.S. treasuries			143,081			143,706			211,055			211,158
Due 1 - 10 years:
Municipal securities			—			—			1,562			1,561
U.S. treasuries			2,077			2,077			6,077			6,078
U.S. government agency securities			—			—			5,267			5,266
Variable rate demand notes			—			—			3,905			3,905
Due 11 - 20 years:
Variable rate demand notes			—			—			8,886			8,886
Due 21 - 30 years:
Variable rate demand notes			—			—			6,885			6,885
Due 31 - 40 years:
Variable rate demand notes			—			—			2,004			2,004
Total		$	252,173		$	252,830		$	545,771		$	545,968