FAIR VALUE MEASUREMENTS - ASSETS MEASURED AT FAIR VALUE (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Mar. 31, 2020
Assets measured at fair value on a recurring basis
Short-term investments	$ 880,825	$ 644,003
Total recurring fair value measurements, net	2,486,105	2,212,804
Money market funds
Assets measured at fair value on a recurring basis
Cash and cash equivalents	498,644	497,861
Restricted cash and cash equivalents	467,298	546,604
Long-term restricted cash and cash equivalents	289,526	89,124
Bank-time deposits
Assets measured at fair value on a recurring basis
Cash and cash equivalents	213,000	313,757
Restricted cash and cash equivalents	324
Short-term investments	352,026	191,000
Commercial paper
Assets measured at fair value on a recurring basis
Cash and cash equivalents	94,105	97,544
Short-term investments	97,910	87,553
Corporate bonds
Assets measured at fair value on a recurring basis
Cash and cash equivalents	37,261	9,888
Short-term investments	401,198	334,631
US Treasuries
Assets measured at fair value on a recurring basis
Short-term investments	28,684	30,819
Asset-backed securities
Assets measured at fair value on a recurring basis
Short-term investments	1,007
Cross-currency swap
Assets measured at fair value on a recurring basis
Prepaid expenses and other		11,275
Private equity
Assets measured at fair value on a recurring basis
Private equity	5,364	2,759
Foreign currency forward contracts
Assets measured at fair value on a recurring basis
Foreign currency forward contracts	(242)	(11)
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	1,849,502	1,669,165
Quoted prices in active markets for identical assets (level 1) | Money market funds
Assets measured at fair value on a recurring basis
Cash and cash equivalents	498,644	497,861
Restricted cash and cash equivalents	467,298	546,604
Long-term restricted cash and cash equivalents	289,526	89,124
Quoted prices in active markets for identical assets (level 1) | Bank-time deposits
Assets measured at fair value on a recurring basis
Cash and cash equivalents	213,000	313,757
Restricted cash and cash equivalents	324
Short-term investments	352,026	191,000
Quoted prices in active markets for identical assets (level 1) | Commercial paper
Assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Short-term investments	0	0
Quoted prices in active markets for identical assets (level 1) | Corporate bonds
Assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Short-term investments	0	0
Quoted prices in active markets for identical assets (level 1) | US Treasuries
Assets measured at fair value on a recurring basis
Short-term investments	28,684	30,819
Quoted prices in active markets for identical assets (level 1) | Asset-backed securities
Assets measured at fair value on a recurring basis
Short-term investments	0
Quoted prices in active markets for identical assets (level 1) | Cross-currency swap
Assets measured at fair value on a recurring basis
Prepaid expenses and other		0
Quoted prices in active markets for identical assets (level 1) | Private equity
Assets measured at fair value on a recurring basis
Private equity	0	0
Quoted prices in active markets for identical assets (level 1) | Foreign currency forward contracts
Assets measured at fair value on a recurring basis
Foreign currency forward contracts	0	0
Significant other observable inputs (level 2)
Assets measured at fair value on a recurring basis
Total recurring fair value measurements, net	631,239	540,880
Significant other observable inputs (level 2) | Money market funds
Assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Restricted cash and cash equivalents	0	0
Long-term restricted cash and cash equivalents	0	0
Significant other observable inputs (level 2) | Bank-time deposits
Assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Restricted cash and cash equivalents	0
Short-term investments	0	0
Significant other observable inputs (level 2) | Commercial paper
Assets measured at fair value on a recurring basis
Cash and cash equivalents	94,105	97,544
Short-term investments	97,910	87,553
Significant other observable inputs (level 2) | Corporate bonds
Assets measured at fair value on a recurring basis
Cash and cash equivalents	37,261	9,888
Short-term investments	401,198	334,631
Significant other observable inputs (level 2) | US Treasuries
Assets measured at fair value on a recurring basis
Short-term investments	0	0
Significant other observable inputs (level 2) | Asset-backed securities
Assets measured at fair value on a recurring basis
Short-term investments	1,007
Significant other observable inputs (level 2) | Cross-currency swap
Assets measured at fair value on a recurring basis
Prepaid expenses and other		11,275
Significant other observable inputs (level 2) | Private equity
Assets measured at fair value on a recurring basis
Private equity	0	0
Significant other observable inputs (level 2) | Foreign currency forward contracts
Assets measured at fair value on a recurring basis
Foreign currency forward contracts	(242)	(11)
Significant unobservable inputs (level 3)
Assets measured at fair value on a recurring basis
Total recurring fair value measurements, net	5,364	2,759
Significant unobservable inputs (level 3) | Money market funds
Assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Restricted cash and cash equivalents	0	0
Long-term restricted cash and cash equivalents	0	0
Significant unobservable inputs (level 3) | Bank-time deposits
Assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Restricted cash and cash equivalents	0
Short-term investments	0	0
Significant unobservable inputs (level 3) | Commercial paper
Assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Short-term investments	0	0
Significant unobservable inputs (level 3) | Corporate bonds
Assets measured at fair value on a recurring basis
Cash and cash equivalents	0	0
Short-term investments	0	0
Significant unobservable inputs (level 3) | US Treasuries
Assets measured at fair value on a recurring basis
Short-term investments	0	0
Significant unobservable inputs (level 3) | Asset-backed securities
Assets measured at fair value on a recurring basis
Short-term investments	0
Significant unobservable inputs (level 3) | Cross-currency swap
Assets measured at fair value on a recurring basis
Prepaid expenses and other		0
Significant unobservable inputs (level 3) | Private equity
Assets measured at fair value on a recurring basis
Private equity	5,364	2,759
Significant unobservable inputs (level 3) | Foreign currency forward contracts
Assets measured at fair value on a recurring basis
Foreign currency forward contracts	$ 0	$ 0