INVESTMENTS (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 55,943		$ 55,943		$ 7,059
Gross Unrealized Gain	0		0		0
Gross Unrealized (Loss)	(107)		(107)		(20)
Fair Value	55,836		55,836		7,039
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	57,214		57,214		66,693
Gross Unrecognized Gain	0		0		1
Gross Unrecognized (Loss)	(254)		(254)		(191)
Fair Value	56,960		56,960		66,503
Unrealized loss position, fair value [Abstract]
Less than 12 Months	89,023		89,023		51,135
12 Months or greater	22,527		22,527		16,108
Total	111,550		111,550		67,243
Unrealized loss position, unrealized loss [Abstract]
Less than 12 Months	(245)		(245)		(198)
12 Months or greater	(116)		(116)		(13)
Total	(361)		(361)		(211)
Available-for-sale securities and Held-to-maturity securities [Abstract]
Other-than-temporary impairment	0	$ 0	0	$ 0	0
Unrealized loss on available-for-sale investments, net of related income taxes	(64)		(64)		(12)
Redemptions of investments with callable provisions	(900)	$ 0	(900)	$ 0
Available-for-sale investments by stated maturity, amortized cost [Abstract]
Amortized Cost, Due in less than one year	49,251		49,251		6,381
Amortized Cost, Due in 1 to 3 years	6,692		6,692		678
Amortized Cost	55,943		55,943		7,059
Available-for-sale investments by stated maturity, fair value [Abstract]
Fair Value, Due in less than one year	49,191		49,191		6,377
Fair Value, Due in 1 to 3 years	6,645		6,645		662
Fair Value, Total investments	55,836		55,836		7,039
Held-to-maturity investments by stated maturity, amortized cost [Abstract]
Amortized Cost, Due in less than one year	40,526		40,526		45,184
Amortized Cost, Due in 1 to 3 years	16,688		16,688		21,509
Amortized Cost, Total investments	57,214		57,214		66,693
Held-to-maturity investments by stated maturity, fair value [Abstract]
Fair Value, Due in less than one year	40,420		40,420		45,124
Fair Value, Due in 1 to 3 years	16,540		16,540		21,379
Fair Value, Total investments	56,960		56,960		66,503
Certificates of Deposit [Member]
Unrealized loss position, fair value [Abstract]
Less than 12 Months	13,133		13,133		2,738
12 Months or greater	0		0		0
Total	13,133		13,133		2,738
Unrealized loss position, unrealized loss [Abstract]
Less than 12 Months	(18)		(18)		(1)
12 Months or greater	0		0		0
Total	(18)		(18)		(1)
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,960		9,960
Gross Unrealized Gain	0		0
Gross Unrealized (Loss)	(6)		(6)
Fair Value	9,954		9,954
Unrealized loss position, fair value [Abstract]
Less than 12 Months	9,954		9,954		2,989
12 Months or greater	0		0		0
Total	9,954		9,954		2,989
Unrealized loss position, unrealized loss [Abstract]
Less than 12 Months	(6)		(6)		(3)
12 Months or greater	0		0		0
Total	(6)		(6)		(3)
Available-for-sale investments by stated maturity, amortized cost [Abstract]
Amortized Cost	9,960		9,960
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	45,323		45,323		6,381
Gross Unrealized Gain	0		0		0
Gross Unrealized (Loss)	(97)		(97)		(4)
Fair Value	45,226		45,226		6,377
Unrealized loss position, fair value [Abstract]
Less than 12 Months	65,280		65,280		44,387
12 Months or greater	22,178		22,178		16,108
Total	87,458		87,458		60,495
Unrealized loss position, unrealized loss [Abstract]
Less than 12 Months	(217)		(217)		(177)
12 Months or greater	(115)		(115)		(13)
Total	(332)		(332)		(190)
Available-for-sale investments by stated maturity, amortized cost [Abstract]
Amortized Cost	45,323		45,323		6,381
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	660		660		678
Gross Unrealized Gain	0		0		0
Gross Unrealized (Loss)	(4)		(4)		(16)
Fair Value	656		656		662
Unrealized loss position, fair value [Abstract]
Less than 12 Months	656		656		1,021
12 Months or greater	349		349		0
Total	1,005		1,005		1,021
Unrealized loss position, unrealized loss [Abstract]
Less than 12 Months	(4)		(4)		(17)
12 Months or greater	(1)		(1)		0
Total	(5)		(5)		(17)
Available-for-sale investments by stated maturity, amortized cost [Abstract]
Amortized Cost	660		660		678
Certificates of Deposit [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	14,397		14,397		3,735
Gross Unrecognized Gain	0		0		1
Gross Unrecognized (Loss)	(18)		(18)		(1)
Fair Value	14,379		14,379		3,735
Held-to-maturity investments by stated maturity, fair value [Abstract]
Fair Value, Total investments	14,379		14,379		3,735
Commercial Paper [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost					5,588
Gross Unrecognized Gain					0
Gross Unrecognized (Loss)					(3)
Fair Value					5,585
Held-to-maturity investments by stated maturity, fair value [Abstract]
Fair Value, Total investments					5,585
Corporate Bonds [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	42,467		42,467		57,009
Gross Unrecognized Gain	0		0		0
Gross Unrecognized (Loss)	(235)		(235)		(186)
Fair Value	42,232		42,232		56,823
Held-to-maturity investments by stated maturity, fair value [Abstract]
Fair Value, Total investments	42,232		42,232		56,823
Municipal Bonds [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	350		350		361
Gross Unrecognized Gain	0		0		0
Gross Unrecognized (Loss)	(1)		(1)		(1)
Fair Value	349		349		360
Held-to-maturity investments by stated maturity, fair value [Abstract]
Fair Value, Total investments	$ 349		$ 349		$ 360