FAIR VALUE MEASUREMENTS - ASSETS MEASURED AT FAIR VALUE (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Jun. 30, 2017	Mar. 31, 2017
Assets measured at fair value on a recurring basis
Total recurring fair value measurements, net	$ 1,018,244	$ 1,186,876
Short-term investments
Assets measured at fair value on a recurring basis
Cash and cash equivalents	200,945	175,745
Corporate bonds	230,015	243,019
Prepaid expenses and other
Assets measured at fair value on a recurring basis
Foreign currency forward contracts	17	2
Accrued and other current liabilities
Assets measured at fair value on a recurring basis
Foreign currency forward contracts	(7,345)	(352)
Other assets
Assets measured at fair value on a recurring basis
Private equity	720	570
Other long-term liabilities
Assets measured at fair value on a recurring basis
Contingent consideration	6,808	6,465
Money market funds | Cash and cash equivalents
Assets measured at fair value on a recurring basis
Cash and cash equivalents	522,035	646,386
Bank-time deposits | Cash and cash equivalents
Assets measured at fair value on a recurring basis
Cash and cash equivalents	35,368	46,605
Commercial paper | Cash and cash equivalents
Assets measured at fair value on a recurring basis
Cash and cash equivalents	7,692	38,268
Commercial paper | Short-term investments
Assets measured at fair value on a recurring basis
Cash and cash equivalents	17,519	25,936
Mutual funds | Short-term investments
Assets measured at fair value on a recurring basis
Cash and cash equivalents	4,470	4,232
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	758,348	868,736
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	200,945	175,745
Corporate bonds	0	0
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	0
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
Quoted prices in active markets for identical assets (level 1) | Other assets
Assets measured at fair value on a recurring basis
Private equity	0	0
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	0
Quoted prices in active markets for identical assets (level 1) | Money market funds | Cash and cash equivalents
Assets measured at fair value on a recurring basis
Cash and cash equivalents	522,035	646,386
Quoted prices in active markets for identical assets (level 1) | Bank-time deposits | Cash and cash equivalents
Assets measured at fair value on a recurring basis
Cash and cash equivalents	35,368	46,605
Quoted prices in active markets for identical assets (level 1) | Commercial paper | Cash and cash equivalents
Assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Quoted prices in active markets for identical assets (level 1) | Commercial paper | Short-term investments
Assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Quoted prices in active markets for identical assets (level 1) | Mutual funds | Short-term investments
Assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Significant other observable inputs (level 2)
Assets measured at fair value on a recurring basis
Total recurring fair value measurements, net	252,368	311,105
Significant other observable inputs (level 2) | Short-term investments
Assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Corporate bonds	230,015	243,019
Significant other observable inputs (level 2) | Prepaid expenses and other
Assets measured at fair value on a recurring basis
Foreign currency forward contracts	17	2
Significant other observable inputs (level 2) | Accrued and other current liabilities
Assets measured at fair value on a recurring basis
Foreign currency forward contracts	(7,345)	(352)
Significant other observable inputs (level 2) | Other assets
Assets measured at fair value on a recurring basis
Private equity	0	0
Significant other observable inputs (level 2) | Other long-term liabilities
Assets measured at fair value on a recurring basis
Contingent consideration	0	0
Significant other observable inputs (level 2) | Money market funds | Cash and cash equivalents
Assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Significant other observable inputs (level 2) | Bank-time deposits | Cash and cash equivalents
Assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Significant other observable inputs (level 2) | Commercial paper | Cash and cash equivalents
Assets measured at fair value on a recurring basis
Cash and cash equivalents	7,692	38,268
Significant other observable inputs (level 2) | Commercial paper | Short-term investments
Assets measured at fair value on a recurring basis
Cash and cash equivalents	17,519	25,936
Significant other observable inputs (level 2) | Mutual funds | Short-term investments
Assets measured at fair value on a recurring basis
Cash and cash equivalents	4,470	4,232
Significant unobservable inputs (level 3)
Assets measured at fair value on a recurring basis
Total recurring fair value measurements, net	7,528	7,035
Significant unobservable inputs (level 3) | Short-term investments
Assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Corporate bonds	0	0
Significant unobservable inputs (level 3) | Prepaid expenses and other
Assets measured at fair value on a recurring basis
Foreign currency forward contracts	0	0
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
Significant unobservable inputs (level 3) | Other assets
Assets measured at fair value on a recurring basis
Private equity	720	570
Significant unobservable inputs (level 3) | Other long-term liabilities
Assets measured at fair value on a recurring basis
Contingent consideration	6,808	6,465
Significant unobservable inputs (level 3) | Money market funds | Cash and cash equivalents
Assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Significant unobservable inputs (level 3) | Bank-time deposits | Cash and cash equivalents
Assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Significant unobservable inputs (level 3) | Commercial paper | Cash and cash equivalents
Assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Significant unobservable inputs (level 3) | Commercial paper | Short-term investments
Assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Significant unobservable inputs (level 3) | Mutual funds | Short-term investments
Assets measured at fair value on a recurring basis
Cash and cash equivalents	$ 0	$ 0