FAIR VALUE MEASUREMENTS - Recurring Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Mar. 31, 2020
Assets measured at fair value on a recurring basis
Short-term investments	$ 772,683	$ 644,003
Total recurring fair value measurements, net	2,602,376	2,212,804
Money market funds
Assets measured at fair value on a recurring basis
Cash and cash equivalents	745,564	497,861
Restricted cash and cash equivalents	469,988	546,604
Long-term restricted cash and cash equivalents	98,538	89,124
Bank time deposits
Assets measured at fair value on a recurring basis
Cash and cash equivalents	471,688	313,757
Short-term investments	118,000	191,000
Restricted cash and cash equivalents	560
Commercial paper
Assets measured at fair value on a recurring basis
Cash and cash equivalents	37,005	97,544
Short-term investments	98,994	87,553
Corporate bonds
Assets measured at fair value on a recurring basis
Cash and cash equivalents	300	9,888
Short-term investments	509,949	334,631
US Treasuries
Assets measured at fair value on a recurring basis
Short-term investments	45,041	30,819
Asset-backed securities
Assets measured at fair value on a recurring basis
Short-term investments	699
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	6,178	2,759
Foreign currency forward contracts
Assets measured at fair value on a recurring basis
Foreign currency forward contracts	(128)	(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	1,949,379	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	745,564	497,861
Restricted cash and cash equivalents	469,988	546,604
Long-term restricted cash and cash equivalents	98,538	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	471,688	313,757
Short-term investments	118,000	191,000
Restricted cash and cash equivalents	560
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	45,041	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	646,819	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
Short-term investments	0	0
Restricted cash and cash equivalents	0
Significant other observable inputs (level 2) | Commercial paper
Assets measured at fair value on a recurring basis
Cash and cash equivalents	37,005	97,544
Short-term investments	98,994	87,553
Significant other observable inputs (level 2) | Corporate bonds
Assets measured at fair value on a recurring basis
Cash and cash equivalents	300	9,888
Short-term investments	509,949	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	699
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	(128)	(11)
Significant unobservable inputs (level 3)
Assets measured at fair value on a recurring basis
Total recurring fair value measurements, net	6,178	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
Short-term investments	0	0
Restricted cash and cash equivalents	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	6,178	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