SHORT-TERM INVESTMENTS (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Sep. 30, 2016	Mar. 31, 2016
Short-term investments:
Cost or Amortized Cost	$ 404,455	$ 470,736
Gross Unrealized Gains	207	131
Gross Unrealized Losses	(71)	(47)
Fair Value	404,591	470,820
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity
Due in 1 year or less	350,866
Due in 1-2 years	53,589
Total amortized cost	404,455
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity
Due in 1 year or less	350,919
Due in 1-2 years	53,672
Total fair value	404,591
Bank time deposits
Short-term investments:
Cost or Amortized Cost	198,072	265,570
Fair Value	198,072	265,570
Corporate bonds
Short-term investments:
Cost or Amortized Cost	206,383	205,166
Gross Unrealized Gains	207	131
Gross Unrealized Losses	(71)	(47)
Fair Value	$ 206,519	$ 205,250