SHORT-TERM INVESTMENTS (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Mar. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	$ 546,524	$ 617,318
Gross Unrealized Gain	106	32
Gross Unrealized Losses	(896)	(1,944)
Fair Value	545,734	615,406
Bank-time deposits
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	152,562	216,663
Gross Unrealized Gain	0	0
Gross Unrealized Losses	0	0
Fair Value	152,562	216,663
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	321,034	310,387
Gross Unrealized Gain	106	16
Gross Unrealized Losses	(783)	(1,687)
Fair Value	320,357	308,716
US Treasuries
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	53,585	59,970
Gross Unrealized Gain	0	0
Gross Unrealized Losses	(113)	(245)
Fair Value	53,472	59,725
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	19,343	25,422
Gross Unrealized Gain	0	0
Gross Unrealized Losses	0	0
Fair Value	$ 19,343	25,422
Mutual funds
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost		4,876
Gross Unrealized Gain		16
Gross Unrealized Losses		(12)
Fair Value		$ 4,880

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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