FAIR VALUE MEASUREMENTS - Schedule of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017
ASSETS:
Cash and cash equivalents	$ 369,821	$ 304,880
Investments	77,941	159,825
Derivative financial instruments	122	110
Total assets	447,884	464,815
LIABILITIES:
Contingent purchase consideration	(5,464)	(5,449)
Derivative financial instruments	(40)	(213)
Total liabilities	(5,504)	(5,662)
U.S. government and municipal obligations
ASSETS:
Investments	42,186	120,901
Commercial paper
ASSETS:
Investments	33,003	29,469
Corporate bonds
ASSETS:
Investments	2,752	7,956
Certificates of deposit
ASSETS:
Investments		1,499
Level 1
ASSETS:
Cash and cash equivalents	369,821	304,880
Derivative financial instruments	0	0
Total assets	387,086	353,464
LIABILITIES:
Contingent purchase consideration	0	0
Derivative financial instruments	0	0
Total liabilities	0	0
Level 1 | U.S. government and municipal obligations
ASSETS:
Investments	14,513	40,628
Level 1 | Commercial paper
ASSETS:
Investments	0	0
Level 1 | Corporate bonds
ASSETS:
Investments	2,752	7,956
Level 1 | Certificates of deposit
ASSETS:
Investments		0
Level 2
ASSETS:
Cash and cash equivalents	0	0
Derivative financial instruments	122	110
Total assets	60,798	111,351
LIABILITIES:
Contingent purchase consideration	0	0
Derivative financial instruments	(40)	(213)
Total liabilities	(40)	(213)
Level 2 | U.S. government and municipal obligations
ASSETS:
Investments	27,673	80,273
Level 2 | Commercial paper
ASSETS:
Investments	33,003	29,469
Level 2 | Corporate bonds
ASSETS:
Investments	0	0
Level 2 | Certificates of deposit
ASSETS:
Investments		1,499
Level 3
ASSETS:
Cash and cash equivalents	0	0
Derivative financial instruments	0	0
Total assets	0	0
LIABILITIES:
Contingent purchase consideration	(5,464)	(5,449)
Derivative financial instruments	0	0
Total liabilities	(5,464)	(5,449)
Level 3 | U.S. government and municipal obligations
ASSETS:
Investments	0	0
Level 3 | Commercial paper
ASSETS:
Investments	0	0
Level 3 | Corporate bonds
ASSETS:
Investments	$ 0	0
Level 3 | Certificates of deposit
ASSETS:
Investments		$ 0