INVESTMENTS (Tables)

12 Months Ended

Dec. 31, 2017

INVESTMENTS

Summary of investments in available-for-sale

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	$	-
December 31, 2016	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	$	40,382	$	-	$	-	$	40,382	$	-	$	-
Municipal securities	140,379		-		181		140,198		181		-
U.S. government agency securities	26,057		-		6		26,051		6		-
Variable rate demand notes	13,923		-		-		13,923		-		-
Long-term:
Municipal securities	2,403		-		9		2,394		9		-
Total	$	223,144	$	-	$	196	$	222,948	$	196	$	-

Summarizes the underlying contractual maturities of the Company's investments

	December 31, 2017				December 31, 2016
	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Less than 1 year:
Commercial paper	$	81,026	$	81,026	$	40,382	$	40,382
Municipal securities	469,604		468,865		140,379		140,198
U.S. government agency securities	61,307		61,219		26,057		26,051
Certificates of deposit	11,869		11,869		-		-
Due 1 -10 years:
Municipal securities	-		-		2,403		2,394
U.S. government agency securities	2,369		2,366		-		-
Variable rate demand notes	6,366		6,366		3,917		3,917
Due 11 - 20 years:
Variable rate demand notes	28,377		28,377		6,003		6,003
Due 21 - 30 years:
Variable rate demand notes	15,211		15,211		4,003		4,003
Total	$	676,129	$	675,299	$	223,144	$	222,948

Schedule of net gain recognized through earnings on trading securities

	2017		2016		2015
Gain (loss) on transfer from available-for-sale to trading	$	-	$	-	$	-
Gain on trading securities sold	-		-		250
(Loss) gain on trading securities held	-		-		-
Gain on trading securites	$	-	$	-	$	250