FAIR VALUE MEASUREMENTS - ASSETS MEASURED AT FAIR VALUE (Details) - Recurring basis - USD ($) $ in Thousands	Sep. 30, 2016	Mar. 31, 2016
Assets measured at fair value on a recurring basis
Total recurring fair value measurements, net	$ 949,295	$ 1,033,409
Cash and Cash Equivalents
Assets measured at fair value on a recurring basis
Money market funds	487,184	562,726
Bank-time deposits	57,518
Short term investments.
Assets measured at fair value on a recurring basis
Corporate bonds	206,519	205,250
Bank-time deposits	198,072	265,570
Prepaid Expenses and other current assets
Assets measured at fair value on a recurring basis
Foreign currency forward contracts	16
Accrued Expenses and other current liabilities
Assets measured at fair value on a recurring basis
Foreign currency forward contracts	(14)	(137)
Quoted prices in active markets for identical assets (level 1)
Assets measured at fair value on a recurring basis
Total recurring fair value measurements, net	742,774	828,296
Quoted prices in active markets for identical assets (level 1) | Cash and Cash Equivalents
Assets measured at fair value on a recurring basis
Money market funds	487,184	562,726
Bank-time deposits	57,518
Quoted prices in active markets for identical assets (level 1) | Short term investments.
Assets measured at fair value on a recurring basis
Bank-time deposits	198,072	265,570
Significant other observable inputs (level 2)
Assets measured at fair value on a recurring basis
Total recurring fair value measurements, net	206,521	205,113
Significant other observable inputs (level 2) | Short term investments.
Assets measured at fair value on a recurring basis
Corporate bonds	206,519	205,250
Significant other observable inputs (level 2) | Prepaid Expenses and other current assets
Assets measured at fair value on a recurring basis
Foreign currency forward contracts	16
Significant other observable inputs (level 2) | Accrued Expenses and other current liabilities
Assets measured at fair value on a recurring basis
Foreign currency forward contracts	$ (14)	$ (137)