FAIR VALUE MEASUREMENTS - Cash, Cash Equivalents and Investments with Hierarchy (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 137,394	$ 276,583	$ 31,703
Accumulated gross unrealized gain, before tax	154	77
Accumulated gross unrealized loss, before tax	(341)	(61)
Cash, cash equivalents and debt securities available-for-sale, amortized cost	187,122	346,466
Cash, cash equivalents and debt securities available-for-sale	186,935	346,482
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents		276,583
Cash and cash equivalents, fair value disclosure		276,583
Accumulated gross unrealized gain, before tax	116
Cash, cash equivalents and debt securities available-for-sale, amortized cost	137,990
Cash, cash equivalents and debt securities available-for-sale	138,106
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Costs	49,132	69,883
Accumulated gross unrealized gain, before tax	38	77
Accumulated gross unrealized loss, before tax	(341)	(61)
Debt securities, available-for-sale	48,829	69,899
Treasuries | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Costs	6,192
Accumulated gross unrealized gain, before tax	116
Debt securities, available-for-sale	6,308
Commercial paper | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Costs	14,979
Accumulated gross unrealized gain, before tax	6
Accumulated gross unrealized loss, before tax	0
Debt securities, available-for-sale	14,985
Corporate debt | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Costs	34,153	46,516
Accumulated gross unrealized gain, before tax	32	51
Accumulated gross unrealized loss, before tax	(341)	(29)
Debt securities, available-for-sale	33,844	46,538
Municipal securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Costs		5,511
Accumulated gross unrealized gain, before tax		17
Accumulated gross unrealized loss, before tax		0
Debt securities, available-for-sale		5,528
Asset backed securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Costs		13,596
Accumulated gross unrealized gain, before tax		9
Accumulated gross unrealized loss, before tax		(17)
Debt securities, available-for-sale		13,588
Agency bond | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Costs		4,260
Accumulated gross unrealized gain, before tax		0
Accumulated gross unrealized loss, before tax		(15)
Debt securities, available-for-sale		4,245
Cash and Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents		276,583
Cash, cash equivalents and debt securities available-for-sale	137,394
Cash and Cash Equivalents | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents		276,583
Cash, cash equivalents and debt securities available-for-sale	131,798
Cash and Cash Equivalents | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	5,596
Cash and Cash Equivalents | Commercial paper | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	5,596
Short-Term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale		69,899
Cash, cash equivalents and debt securities available-for-sale	33,458
Short-Term Investments | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	33,458	69,899
Short-Term Investments | Commercial paper | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	9,389
Short-Term Investments | Corporate debt | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	24,069	46,538
Short-Term Investments | Municipal securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale		5,528
Short-Term Investments | Asset backed securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale		13,588
Short-Term Investments | Agency bond | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale		4,245
Long-Term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, cash equivalents and debt securities available-for-sale	16,083
Long-Term Investments | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	6,308
Long-Term Investments | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	9,775
Long-Term Investments | Treasuries | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	6,308
Long-Term Investments | Corporate debt | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale	9,775
Cash
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	21,002	25,364
Cash and cash equivalents, fair value disclosure	21,002	25,364
Cash | Cash and Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	21,002	25,364
Money market funds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	110,796	251,219
Cash and cash equivalents, fair value disclosure	110,796	251,219
Money market funds | Cash and Cash Equivalents | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 110,796	$ 251,219