CASH, CASH EQUIVALENTS, AND INVESTMENTS (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	May 31, 2015
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	$ 156,821	$ 202,509	$ 328,156	$ 390,661
Short-term investments (due in 1 year or less)	15,317	13,332
Total cash, cash equivalents and investments measured at fair value, amortized cost	171,464	215,929
Total cash, cash equivalents and investments measured at fair value, gross unrealized gains	745	197
Total cash, cash equivalents and investments measured at fair value, gross unrealized losses	(71)	(285)
Total cash, cash equivalents and investments measured at fair value, fair value	172,138	215,841
Cash [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	156,821	202,509
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	14,643	13,420
Available-for-sale Securities, gross unrealized gains	745	197
Available-for-sale Securities, gross unrealized losses	(71)	(285)
Available-for-sale Securities, fair value	15,317	13,332
Short-term investments (due in 1 year or less)	$ 15,317	$ 13,332
5.50% Senior Notes [Member] | Senior Notes [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Stated interest rate of debt instrument	5.50%				5.50%