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INVESTMENTS (Tables)

6 Months Ended

Jun. 30, 2019

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, 2019		Cost			Gains			Losses			Value			Months			Months
Available-for-sale
Short-term:
Commercial paper		$	63,286		$	-		$	-		$	63,286		$	-		$	-
Certificates of deposit			15,026			-			-			15,026			-			-
Municipal securities			104,230			80			3			104,307			3			-
U.S. government agency securities			20,430			17			-			20,447			-			-
U.S. treasuries			131,508			141			2			131,647			2			-
Variable rate demand notes			23,275			-			-			23,275			-			-
Long-term:
Municipal securities			6,992			14			-			7,006			-			-
Total		$	364,747		$	252		$	5		$	364,994		$	5		$	-


														Continuous			Continuous
					Gross			Gross						Unrealized			Unrealized
					Unrealized			Unrealized						Loss Position			Loss Position
		Amortized			Holding			Holding			Fair			less than 12			greater than 12
December 31, 2018		Cost			Gains			Losses			Value			Months			Months
Available-for-sale
Short-term:
Commercial paper		$	52,838		$	-		$	-		$	52,838		$	-		$	-
Certificates of deposit			14,075			-			-			14,075			-			-
Municipal securities			151,690			16			62			151,644			62			-
U.S. government agency securities			19,943			-			12			19,931			12			-
U.S. treasuries			78,189			-			32			78,157			32			-
Variable rate demand notes			4,005			-			-			4,005			-			-
Total		$	320,740		$	16		$	106		$	320,650		$	106		$	-

Summary of the underlying contractual maturities of investments


		June 30, 2019						December 31, 2018
		Amortized Cost			Fair Value			Amortized Cost			Fair Value
Less than 1 year:
Commercial paper		$	63,286		$	63,286		$	52,838		$	52,838
Municipal securities			104,230			104,307			151,690			151,644
U.S. government agency securities			20,430			20,447			19,943			19,931
Certificates of deposit			15,026			15,026			14,075			14,075
U.S. treasuries			131,508			131,647			78,189			78,157
Due 1 - 10 years:
Municipal securities			6,992			7,006			-			-
Variable rate demand notes			2,442			2,442			-			-
Due 11 - 20 years:
Variable rate demand notes			17,924			17,924			-			-
Due 21 - 30 years:
Variable rate demand notes			2,909			2,909			4,005			4,005
Total		$	364,747		$	364,994		$	320,740		$	320,650