CASH, CASH EQUIVALENTS, AND INVESTMENTS (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Mar. 31, 2018	May 31, 2015
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	$ 186,442	$ 202,509	$ 291,086	$ 390,661
Short-term investments (due in 1 year or less)	14,378	13,332
Total cash, cash equivalents and investments measured at fair value, amortized cost	200,542	215,929
Total cash, cash equivalents and investments measured at fair value, gross unrealized gains	361	197
Total cash, cash equivalents and investments measured at fair value, gross unrealized losses	(83)	(285)
Total cash, cash equivalents and investments measured at fair value, fair value	200,820	215,841
Cash [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	186,442	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	14,100	13,420
Available-for-sale Securities, gross unrealized gains	361	197
Available-for-sale Securities, gross unrealized losses	(83)	(285)
Available-for-sale Securities, fair value	14,378	13,332
Short-term investments (due in 1 year or less)	$ 14,378	$ 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%