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INVESTMENTS (Tables)

9 Months Ended

Sep. 30, 2018

INVESTMENTS

Summary of investments in available-for-sale

September 30, 2018		Amortized Cost			Gross Unrealized Holding Gains			Gross Unrealized Holding Losses			Fair Value			Continuous Unrealized Loss Position less than 12 Months			Continuous Unrealized Loss Position greater than 12 Months
Available-for-sale
Short-term:
Commercial paper		$	52,595		$	-		$	-		$	52,595		$	-		$	-
Certificates of deposit		26,068			-			-			26,068			-			-
Municipal securities		127,149			2			82			127,069			82			-
U.S. government agency securities		108,128			-			95			108,033			95			-
U.S. Treasuries		109,832			-			45			109,787			45			-
Variable rate demand notes		34,346			-			-			34,346			-			-
Long-term:
Municipal securities		1,612			-			2			1,610			2			-
Total		$	459,730		$	2		$	224		$	459,508		$	224		$	-

December 31, 2017		Amortized Cost			Gross Unrealized Holding Gains			Gross Unrealized Holding Losses			Fair Value			Continuous Unrealized Loss Position less than 12 Months			Continuous Unrealized Loss Position greater than 12 Months
Available-for-sale
Short-term:
Commercial paper		$	81,026		$	-		$	-		$	81,026		$	-		$	-
Certificates of deposit		11,869			-			-			11,869			-			-
Municipal securities		469,604			1			740			468,865			740			-
U.S. government agency securities		61,307			-			88			61,219			88			-
Variable rate demand notes		49,954			-			-			49,954			-			-
Long-term:
U.S. government agency securities		2,369			-			3			2,366			3			-
Total		$	676,129		$	1		$	831		$	675,299		$	831		$	-

Summary of the underlying contractual maturities of investments

		September 30, 2018						December 31, 2017
		Amortized Cost			Fair Value			Amortized Cost			Fair Value
Less than 1 year:
Commercial paper		$	52,595		$	52,595		$	81,026		$	81,026
U.S. Treasuries		109,832			109,787			-			-
Municipal securities		127,149			127,069			469,604			468,865
U.S. government agency securities		108,128			108,033			61,307			61,219
Certificates of deposit		26,068			26,068			11,869			11,869
Due 1 - 10 years:
Municipal securities		1,612			1,610			-			-
U.S. government agency securities		-			-			2,369			2,366
Variable rate demand notes		-			-			6,366			6,366
Due 11 - 20 years:
Variable rate demand notes		15,952			15,952			28,377			28,377
Due 21 - 30 years:
Variable rate demand notes		14,291			14,291			15,211			15,211
Due 31 - 40 years:
Variable rate demand notes		4,103			4,103			-			-
Total		$	459,730		$	459,508		$	676,129		$	675,299

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