CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES - Summary of Cash, Cash Equivalent and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 369,821	$ 304,880	$ 210,711	$ 104,893
Restricted cash	910	846	186	186
Total cash, cash equivalents and restricted cash	$ 370,731	$ 305,726	$ 210,897	$ 105,079