CASH, CASH EQUIVALENTS, RESTRICTED CASH AND MARKETABLE SECURITIES - Summary of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Mar. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Cash and cash equivalents	$ 332,183	$ 369,821	$ 251,505	$ 304,880
Restricted cash	187	910	909	846
Total cash, cash equivalents and restricted cash	$ 332,370	$ 370,731	$ 252,414	$ 305,726

Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Name:	us-gaap_RestrictedCashAndCashEquivalents
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant