FAIR VALUE MEASUREMENTS - Schedule of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Mar. 31, 2019
ASSETS:
Cash and cash equivalents	$ 245,064	$ 409,632
Available-for-sale securities	62,759	77,356
Derivative financial instruments	37	58
Contingent consideration	245	762
Total assets	308,105	487,808
LIABILITIES:
Contingent purchase consideration	(1,000)
Derivative financial instruments	(35)	(68)
Total liabilities	(1,035)	(68)
U.S. government and municipal obligations
ASSETS:
Available-for-sale securities	33,280	27,622
Commercial paper
ASSETS:
Available-for-sale securities	25,289	48,722
Corporate bonds
ASSETS:
Available-for-sale securities	4,190	1,012
Level 1
ASSETS:
Cash and cash equivalents	245,064	409,632
Derivative financial instruments	0	0
Contingent consideration	0	0
Total assets	282,534	421,376
LIABILITIES:
Contingent purchase consideration	0
Derivative financial instruments	0	0
Total liabilities	0	0
Level 1 | U.S. government and municipal obligations
ASSETS:
Available-for-sale securities	33,280	10,732
Level 1 | Commercial paper
ASSETS:
Available-for-sale securities	0	0
Level 1 | Corporate bonds
ASSETS:
Available-for-sale securities	4,190	1,012
Level 2
ASSETS:
Cash and cash equivalents	0	0
Derivative financial instruments	37	58
Contingent consideration	0	0
Total assets	25,326	65,670
LIABILITIES:
Contingent purchase consideration	0
Derivative financial instruments	(35)	(68)
Total liabilities	(35)	(68)
Level 2 | U.S. government and municipal obligations
ASSETS:
Available-for-sale securities		16,890
Level 2 | Commercial paper
ASSETS:
Available-for-sale securities	25,289	48,722
Level 2 | Corporate bonds
ASSETS:
Available-for-sale securities	0	0
Level 3
ASSETS:
Cash and cash equivalents	0	0
Derivative financial instruments	0	0
Contingent consideration	245	762
Total assets	245	762
LIABILITIES:
Contingent purchase consideration	(1,000)
Derivative financial instruments	0	0
Total liabilities	(1,000)	0
Level 3 | U.S. government and municipal obligations
ASSETS:
Available-for-sale securities	0	0
Level 3 | Commercial paper
ASSETS:
Available-for-sale securities	0	0
Level 3 | Corporate bonds
ASSETS:
Available-for-sale securities	$ 0	$ 0