FAIR VALUE MEASUREMENTS - Schedule of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Mar. 31, 2017
ASSETS:
Cash and cash equivalents	$ 251,505	$ 304,880
Available-for-sale securities	61,874	159,825
Derivative financial instruments	496	110
Total assets	313,875	464,815
LIABILITIES:
Contingent purchase consideration	(5,388)	(5,449)
Derivative financial instruments	(18)	(213)
Total liabilities	(5,406)	(5,662)
U.S. government and municipal obligations
ASSETS:
Available-for-sale securities	46,888	120,901
Commercial paper
ASSETS:
Available-for-sale securities	13,984	29,469
Corporate bonds
ASSETS:
Available-for-sale securities	1,002	7,956
Certificate of deposits
ASSETS:
Available-for-sale securities		1,499
Level 1
ASSETS:
Cash and cash equivalents	251,505	304,880
Derivative financial instruments	0	0
Total assets	274,301	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:
Available-for-sale securities	21,794	40,628
Level 1 | Commercial paper
ASSETS:
Available-for-sale securities	0	0
Level 1 | Corporate bonds
ASSETS:
Available-for-sale securities	1,002	7,956
Level 1 | Certificate of deposits
ASSETS:
Available-for-sale securities		0
Level 2
ASSETS:
Cash and cash equivalents	0	0
Derivative financial instruments	496	110
Total assets	39,574	111,351
LIABILITIES:
Contingent purchase consideration	0	0
Derivative financial instruments	(18)	(213)
Total liabilities	(18)	(213)
Level 2 | U.S. government and municipal obligations
ASSETS:
Available-for-sale securities	25,094	80,273
Level 2 | Commercial paper
ASSETS:
Available-for-sale securities	13,984	29,469
Level 2 | Corporate bonds
ASSETS:
Available-for-sale securities	0	0
Level 2 | Certificate of deposits
ASSETS:
Available-for-sale securities		1,499
Level 3
ASSETS:
Cash and cash equivalents	0	0
Derivative financial instruments	0	0
Total assets	0	0
LIABILITIES:
Contingent purchase consideration	(5,388)	(5,449)
Derivative financial instruments	0	0
Total liabilities	(5,388)	(5,449)
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
Level 3 | Certificate of deposits
ASSETS:
Available-for-sale securities		$ 0