FAIR VALUE MEASUREMENTS - Schedule of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Mar. 31, 2018
ASSETS:
Cash and cash equivalents	$ 353,416	$ 369,821
Available-for-sale securities	105,637	77,941
Derivative financial instruments		122
Total assets	459,053	447,884
LIABILITIES:
Contingent purchase consideration	(5,502)	(5,464)
Derivative financial instruments	(381)	(40)
Total liabilities	(5,883)	(5,504)
U.S. government and municipal obligations
ASSETS:
Available-for-sale securities	46,015	42,186
Commercial paper
ASSETS:
Available-for-sale securities	56,877	33,003
Corporate bonds
ASSETS:
Available-for-sale securities	2,745	2,752
Level 1
ASSETS:
Cash and cash equivalents	353,416	369,821
Derivative financial instruments		0
Total assets	371,432	387,086
LIABILITIES:
Contingent purchase consideration	0	0
Derivative financial instruments	0	0
Total liabilities	0	0
Level 1 | U.S. government and municipal obligations
ASSETS:
Available-for-sale securities	15,271	14,513
Level 1 | Commercial paper
ASSETS:
Available-for-sale securities	0	0
Level 1 | Corporate bonds
ASSETS:
Available-for-sale securities	2,745	2,752
Level 2
ASSETS:
Derivative financial instruments		122
Total assets	87,621	60,798
LIABILITIES:
Contingent purchase consideration	0	0
Derivative financial instruments	(381)	(40)
Total liabilities	(381)	(40)
Level 2 | U.S. government and municipal obligations
ASSETS:
Available-for-sale securities	30,744	27,673
Level 2 | Commercial paper
ASSETS:
Available-for-sale securities	56,877	33,003
Level 2 | Corporate bonds
ASSETS:
Available-for-sale securities	0	0
Level 3
ASSETS:
Derivative financial instruments		0
Total assets	0	0
LIABILITIES:
Contingent purchase consideration	(5,502)	(5,464)
Derivative financial instruments	0	0
Total liabilities	(5,502)	(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