FAIR VALUE MEASUREMENTS - ASSETS MEASURED AT FAIR VALUE (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Mar. 31, 2016
Assets measured at fair value on a recurring basis
Contingent consideration	$ 6,465
Fair Value, Measurements, Recurring
Assets measured at fair value on a recurring basis
Total recurring fair value measurements, net	1,186,876	$ 1,033,409
Fair Value, Measurements, Recurring | Short-term investments
Assets measured at fair value on a recurring basis
Cash and cash equivalents, fair value disclosure	175,745	265,570
Corporate bonds	273,187	205,250
Fair Value, Measurements, Recurring | Prepaid expenses and other
Assets measured at fair value on a recurring basis
Foreign currency forward contracts	2
Fair Value, Measurements, Recurring | Accrued and other current liabilities
Assets measured at fair value on a recurring basis
Foreign currency forward contracts	(352)	(137)
Fair Value, Measurements, Recurring | Other assets
Assets measured at fair value on a recurring basis
Private equity	570
Fair Value, Measurements, Recurring | Other long-term liabilities
Assets measured at fair value on a recurring basis
Contingent consideration	6,465
Fair Value, Measurements, Recurring | 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	868,736	828,296
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (level 1) | Short-term investments
Assets measured at fair value on a recurring basis
Cash and cash equivalents, fair value disclosure	175,745	265,570
Corporate bonds	0	0
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (level 1) | Prepaid expenses and other
Assets measured at fair value on a recurring basis
Foreign currency forward contracts	0
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (level 1) | Accrued and other current liabilities
Assets measured at fair value on a recurring basis
Foreign currency forward contracts	0	0
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (level 1) | Other assets
Assets measured at fair value on a recurring basis
Private equity	0
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets (level 1) | Other long-term liabilities
Assets measured at fair value on a recurring basis
Contingent consideration	0
Fair Value, Measurements, Recurring | Significant other observable inputs (level 2)
Assets measured at fair value on a recurring basis
Total recurring fair value measurements, net	311,105	205,113
Fair Value, Measurements, Recurring | Significant other observable inputs (level 2) | Short-term investments
Assets measured at fair value on a recurring basis
Cash and cash equivalents, fair value disclosure	0	0
Corporate bonds	273,187	205,250
Fair Value, Measurements, Recurring | Significant other observable inputs (level 2) | Prepaid expenses and other
Assets measured at fair value on a recurring basis
Foreign currency forward contracts	2
Fair Value, Measurements, Recurring | Significant other observable inputs (level 2) | Accrued and other current liabilities
Assets measured at fair value on a recurring basis
Foreign currency forward contracts	(352)	(137)
Fair Value, Measurements, Recurring | Significant other observable inputs (level 2) | Other assets
Assets measured at fair value on a recurring basis
Private equity	0
Fair Value, Measurements, Recurring | Significant other observable inputs (level 2) | Other long-term liabilities
Assets measured at fair value on a recurring basis
Contingent consideration	0
Fair Value, Measurements, Recurring | Significant unobservable inputs (level 3)
Assets measured at fair value on a recurring basis
Total recurring fair value measurements, net	7,035	0
Fair Value, Measurements, Recurring | Significant unobservable inputs (level 3) | Short-term investments
Assets measured at fair value on a recurring basis
Cash and cash equivalents, fair value disclosure	0	0
Corporate bonds	0	0
Fair Value, Measurements, Recurring | Significant unobservable inputs (level 3) | Prepaid expenses and other
Assets measured at fair value on a recurring basis
Foreign currency forward contracts	0
Fair Value, Measurements, Recurring | Significant unobservable inputs (level 3) | Accrued and other current liabilities
Assets measured at fair value on a recurring basis
Foreign currency forward contracts	0	0
Fair Value, Measurements, Recurring | Significant unobservable inputs (level 3) | Other assets
Assets measured at fair value on a recurring basis
Private equity	570
Fair Value, Measurements, Recurring | Significant unobservable inputs (level 3) | Other long-term liabilities
Assets measured at fair value on a recurring basis
Contingent consideration	6,465
Fair Value, Measurements, Recurring | Money market funds | Cash and cash equivalents
Assets measured at fair value on a recurring basis
Cash and cash equivalents, fair value disclosure	646,386	562,726
Fair Value, Measurements, Recurring | Money market funds | Quoted prices in active markets for identical assets (level 1) | Cash and cash equivalents
Assets measured at fair value on a recurring basis
Cash and cash equivalents, fair value disclosure	646,386	562,726
Fair Value, Measurements, Recurring | Money market funds | Significant other observable inputs (level 2) | Cash and cash equivalents
Assets measured at fair value on a recurring basis
Cash and cash equivalents, fair value disclosure	0	0
Fair Value, Measurements, Recurring | Money market funds | Significant unobservable inputs (level 3) | Cash and cash equivalents
Assets measured at fair value on a recurring basis
Cash and cash equivalents, fair value disclosure	0	$ 0
Fair Value, Measurements, Recurring | Bank-time deposits | Cash and cash equivalents
Assets measured at fair value on a recurring basis
Cash and cash equivalents, fair value disclosure	46,605
Fair Value, Measurements, Recurring | Bank-time deposits | Quoted prices in active markets for identical assets (level 1) | Cash and cash equivalents
Assets measured at fair value on a recurring basis
Cash and cash equivalents, fair value disclosure	46,605
Fair Value, Measurements, Recurring | Bank-time deposits | Significant other observable inputs (level 2) | Cash and cash equivalents
Assets measured at fair value on a recurring basis
Cash and cash equivalents, fair value disclosure	0
Fair Value, Measurements, Recurring | Bank-time deposits | Significant unobservable inputs (level 3) | Cash and cash equivalents
Assets measured at fair value on a recurring basis
Cash and cash equivalents, fair value disclosure	0
Fair Value, Measurements, Recurring | Commercial paper | Cash and cash equivalents
Assets measured at fair value on a recurring basis
Cash and cash equivalents, fair value disclosure	38,268
Fair Value, Measurements, Recurring | Commercial paper | Quoted prices in active markets for identical assets (level 1) | Cash and cash equivalents
Assets measured at fair value on a recurring basis
Cash and cash equivalents, fair value disclosure	0
Fair Value, Measurements, Recurring | Commercial paper | Significant other observable inputs (level 2) | Cash and cash equivalents
Assets measured at fair value on a recurring basis
Cash and cash equivalents, fair value disclosure	38,268
Fair Value, Measurements, Recurring | Commercial paper | Significant unobservable inputs (level 3) | Cash and cash equivalents
Assets measured at fair value on a recurring basis
Cash and cash equivalents, fair value disclosure	$ 0