FAIR VALUE MEASUREMENTS - Schedule of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Mar. 31, 2018
ASSETS:
Cash and cash equivalents	$ 369,054	$ 369,821
Available-for-sale securities	106,755	77,941
Derivative financial instruments	21	122
Contingent consideration	2,321
Total assets	478,151	447,884
LIABILITIES:
Contingent purchase consideration		(5,464)
Derivative financial instruments	(224)	(40)
Total liabilities	(224)	(5,504)
U.S. government and municipal obligations
ASSETS:
Available-for-sale securities	53,965	42,186
Commercial paper
ASSETS:
Available-for-sale securities	50,783	33,003
Corporate bonds
ASSETS:
Available-for-sale securities	2,007	2,752
Level 1
ASSETS:
Cash and cash equivalents	369,054	369,821
Derivative financial instruments	0	0
Contingent consideration	0
Total assets	406,729	387,086
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	35,668	14,513
Level 1 | Commercial paper
ASSETS:
Available-for-sale securities	0	0
Level 1 | Corporate bonds
ASSETS:
Available-for-sale securities	2,007	2,752
Level 2
ASSETS:
Derivative financial instruments	21	122
Contingent consideration	0
Total assets	69,101	60,798
LIABILITIES:
Contingent purchase consideration		0
Derivative financial instruments	(224)	(40)
Total liabilities	(224)	(40)
Level 2 | U.S. government and municipal obligations
ASSETS:
Available-for-sale securities	18,297	27,673
Level 2 | Commercial paper
ASSETS:
Available-for-sale securities	50,783	33,003
Level 2 | Corporate bonds
ASSETS:
Available-for-sale securities	0	0
Level 3
ASSETS:
Derivative financial instruments	0	0
Contingent consideration	2,321
Total assets	2,321	0
LIABILITIES:
Contingent purchase consideration		(5,464)
Derivative financial instruments	0	0
Total liabilities	0	(5,464)
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