CASH, CASH EQUIVALENTS, AND INVESTMENTS (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2016	Mar. 31, 2016
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	$ 290,484	$ 301,970	$ 227,473	$ 235,266
Short-term investments (due in 1 year or less)	196,992	178,179
Long-term investments (due in 1 to 3 years)	112,090	127,176
Total cash, cash equivalents and investments measured at fair value, amortized cost	599,449	607,374
Total cash, cash equivalents and investments measured at fair value, gross unrealized gains	542	439
Total cash, cash equivalents and investments measured at fair value, gross unrealized losses	(425)	(488)
Total cash, cash equivalents and investments measured at fair value, fair value	599,566	607,325
Cash [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	283,289	295,877
Level 1 [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	0	0
Available-for-sale Securities, amortized cost basis	52,057	48,039
Available-for-sale Securities, gross unrealized gains	436	352
Available-for-sale Securities, gross unrealized losses	(105)	(100)
Available-for-sale Securities, fair value	52,388	48,291
Short-term investments (due in 1 year or less)	33,969	29,959
Long-term investments (due in 1 to 3 years)	18,419	18,332
Level 1 [Member] | Mutual Funds [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	0	0
Available-for-sale Securities, amortized cost basis	13,143	12,079
Available-for-sale Securities, gross unrealized gains	436	352
Available-for-sale Securities, gross unrealized losses	(27)	(32)
Available-for-sale Securities, fair value	13,552	12,399
Short-term investments (due in 1 year or less)	13,552	12,399
Long-term investments (due in 1 to 3 years)	0	0
Level 1 [Member] | US Treasury Notes [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	0	0
Available-for-sale Securities, amortized cost basis	38,914	35,960
Available-for-sale Securities, gross unrealized gains	0	0
Available-for-sale Securities, gross unrealized losses	(78)	(68)
Available-for-sale Securities, fair value	38,836	35,892
Short-term investments (due in 1 year or less)	20,417	17,560
Long-term investments (due in 1 to 3 years)	18,419	18,332
Level 2 [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	7,195	6,093
Available-for-sale Securities, amortized cost basis	264,103	263,458
Available-for-sale Securities, gross unrealized gains	106	87
Available-for-sale Securities, gross unrealized losses	(320)	(388)
Available-for-sale Securities, fair value	263,889	263,157
Short-term investments (due in 1 year or less)	163,023	148,220
Long-term investments (due in 1 to 3 years)	93,671	108,844
Level 2 [Member] | Government Agency Securities [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	0	0
Available-for-sale Securities, amortized cost basis	52,412	54,415
Available-for-sale Securities, gross unrealized gains	0	20
Available-for-sale Securities, gross unrealized losses	(172)	(164)
Available-for-sale Securities, fair value	52,240	54,271
Short-term investments (due in 1 year or less)	31,739	15,309
Long-term investments (due in 1 to 3 years)	20,501	38,962
Level 2 [Member] | Commercial Paper [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	7,195	6,093
Available-for-sale Securities, amortized cost basis	47,642	47,152
Available-for-sale Securities, gross unrealized gains	0	0
Available-for-sale Securities, gross unrealized losses	0	0
Available-for-sale Securities, fair value	47,642	47,152
Short-term investments (due in 1 year or less)	40,447	41,059
Long-term investments (due in 1 to 3 years)	0	0
Level 2 [Member] | Corporate Bonds [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	0	0
Available-for-sale Securities, amortized cost basis	145,498	141,508
Available-for-sale Securities, gross unrealized gains	97	64
Available-for-sale Securities, gross unrealized losses	(148)	(224)
Available-for-sale Securities, fair value	145,447	141,348
Short-term investments (due in 1 year or less)	73,493	73,676
Long-term investments (due in 1 to 3 years)	71,954	67,672
Level 2 [Member] | Certificates of Deposit [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	0	0
Available-for-sale Securities, amortized cost basis	18,551	20,383
Available-for-sale Securities, gross unrealized gains	9	3
Available-for-sale Securities, gross unrealized losses	0	0
Available-for-sale Securities, fair value	18,560	20,386
Short-term investments (due in 1 year or less)	17,344	18,176
Long-term investments (due in 1 to 3 years)	$ 1,216	$ 2,210