FAIR VALUE MEASUREMENTS - Schedule of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Mar. 31, 2017
ASSETS:
Cash and cash equivalents	$ 331,912	$ 304,880
Available-for-sale securities	51,082	159,825
Derivative financial instruments	153	110
Total assets	383,147	464,815
LIABILITIES:
Contingent purchase consideration	(5,426)	(5,449)
Derivative financial instruments	(63)	(213)
Total liabilities	(5,489)	(5,662)
U.S. government and municipal obligations
ASSETS:
Available-for-sale securities	45,070	120,901
Commercial paper
ASSETS:
Available-for-sale securities	5,007	29,469
Corporate bonds
ASSETS:
Available-for-sale securities	1,005	7,956
Certificate of deposits
ASSETS:
Available-for-sale securities		1,499
Level 1
ASSETS:
Cash and cash equivalents	331,912	304,880
Derivative financial instruments	0	0
Total assets	349,927	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	17,010	40,628
Level 1 | Commercial paper
ASSETS:
Available-for-sale securities	0	0
Level 1 | Corporate bonds
ASSETS:
Available-for-sale securities	1,005	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	153	110
Total assets	33,220	111,351
LIABILITIES:
Contingent purchase consideration	0	0
Derivative financial instruments	(63)	(213)
Total liabilities	(63)	(213)
Level 2 | U.S. government and municipal obligations
ASSETS:
Available-for-sale securities	28,060	80,273
Level 2 | Commercial paper
ASSETS:
Available-for-sale securities	5,007	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	(5,426)	(5,449)
Derivative financial instruments	0	0
Total liabilities	(5,426)	(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