CASH, CASH EQUIVALENTS, AND INVESTMENTS (Details) - USD ($) $ in Thousands | Dec. 31, 2015 | Mar. 31, 2015 | Dec. 31, 2014 | Mar. 31, 2014 |
Schedule of Cash, Cash Equivalents and Investments [Line Items] | | | | |
Cash and cash equivalents | $ 219,091 | $ 276,850 | $ 280,350 | $ 232,704 |
Short-term investments (due in 1 year or less) | 166,257 | 97,859 | | |
Long-term investments (due in 1 to 3 years) | 135,164 | 107,590 | | |
Total cash, cash equivalents and investments measured at fair value, amortized cost | 521,683 | 481,956 | | |
Total cash, cash equivalents and investments measured at fair value, gross unrealized gains | 24 | 393 | | |
Total cash, cash equivalents and investments measured at fair value, gross unrealized losses | (1,195) | (50) | | |
Total cash, cash equivalents and investments measured at fair value, fair value | 520,512 | 482,299 | | |
Cash [Member] | | | | |
Schedule of Cash, Cash Equivalents and Investments [Line Items] | | | | |
Cash and cash equivalents | 209,379 | 273,350 | | |
Level 1 [Member] | | | | |
Schedule of Cash, Cash Equivalents and Investments [Line Items] | | | | |
Cash and cash equivalents | 4,006 | | | |
Available-for-sale Securities, amortized cost basis | 49,319 | | | |
Available-for-sale Securities, gross unrealized gains | 1 | | | |
Available-for-sale Securities, gross unrealized losses | (642) | | | |
Available-for-sale Securities, fair value | 48,678 | | | |
Short-term investments (due in 1 year or less) | 24,952 | | | |
Long-term investments (due in 1 to 3 years) | 19,720 | | | |
Level 1 [Member] | Mutual Funds [Member] | | | | |
Schedule of Cash, Cash Equivalents and Investments [Line Items] | | | | |
Available-for-sale Securities, amortized cost basis | 9,497 | 5,398 | | |
Available-for-sale Securities, gross unrealized gains | 1 | 147 | | |
Available-for-sale Securities, gross unrealized losses | (546) | (25) | | |
Available-for-sale Securities, fair value | 8,952 | 5,520 | | |
Short-term investments (due in 1 year or less) | 8,952 | 5,520 | | |
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 | 4,006 | | | |
Available-for-sale Securities, amortized cost basis | 39,822 | | | |
Available-for-sale Securities, gross unrealized gains | 0 | | | |
Available-for-sale Securities, gross unrealized losses | (96) | | | |
Available-for-sale Securities, fair value | 39,726 | | | |
Short-term investments (due in 1 year or less) | 16,000 | | | |
Long-term investments (due in 1 to 3 years) | 19,720 | | | |
Level 2 [Member] | | | | |
Schedule of Cash, Cash Equivalents and Investments [Line Items] | | | | |
Cash and cash equivalents | 5,706 | 3,500 | | |
Available-for-sale Securities, amortized cost basis | 262,985 | 203,208 | | |
Available-for-sale Securities, gross unrealized gains | 23 | 246 | | |
Available-for-sale Securities, gross unrealized losses | (553) | (25) | | |
Available-for-sale Securities, fair value | 262,455 | 203,429 | | |
Short-term investments (due in 1 year or less) | 141,305 | 92,339 | | |
Long-term investments (due in 1 to 3 years) | 115,444 | 107,590 | | |
Level 2 [Member] | Government Agency Securities [Member] | | | | |
Schedule of Cash, Cash Equivalents and Investments [Line Items] | | | | |
Available-for-sale Securities, amortized cost basis | 70,680 | 89,875 | | |
Available-for-sale Securities, gross unrealized gains | 1 | 37 | | |
Available-for-sale Securities, gross unrealized losses | (178) | (22) | | |
Available-for-sale Securities, fair value | 70,503 | 89,890 | | |
Short-term investments (due in 1 year or less) | 20,919 | 43,024 | | |
Long-term investments (due in 1 to 3 years) | 49,584 | 46,866 | | |
Level 2 [Member] | Commercial Paper [Member] | | | | |
Schedule of Cash, Cash Equivalents and Investments [Line Items] | | | | |
Cash and cash equivalents | 4,199 | 3,500 | | |
Available-for-sale Securities, amortized cost basis | 40,196 | 17,574 | | |
Available-for-sale Securities, gross unrealized gains | 0 | 10 | | |
Available-for-sale Securities, gross unrealized losses | 0 | 0 | | |
Available-for-sale Securities, fair value | 40,196 | 17,584 | | |
Short-term investments (due in 1 year or less) | 35,702 | 14,084 | | |
Long-term investments (due in 1 to 3 years) | 295 | 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 | 143,139 | 95,759 | | |
Available-for-sale Securities, gross unrealized gains | 22 | 199 | | |
Available-for-sale Securities, gross unrealized losses | (375) | (3) | | |
Available-for-sale Securities, fair value | 142,786 | 95,955 | | |
Short-term investments (due in 1 year or less) | 77,221 | 35,231 | | |
Long-term investments (due in 1 to 3 years) | 65,565 | $ 60,724 | | |
Level 2 [Member] | Certificates of Deposit [Member] | | | | |
Schedule of Cash, Cash Equivalents and Investments [Line Items] | | | | |
Cash and cash equivalents | 1,507 | | | |
Available-for-sale Securities, amortized cost basis | 8,970 | | | |
Available-for-sale Securities, gross unrealized gains | 0 | | | |
Available-for-sale Securities, gross unrealized losses | 0 | | | |
Available-for-sale Securities, fair value | 8,970 | | | |
Short-term investments (due in 1 year or less) | 7,463 | | | |
Long-term investments (due in 1 to 3 years) | $ 0 | | | |