FAIR VALUE OF FINANCIAL INSTRUMENTS: (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Mar. 31, 2019
Fair value of assets and liabilities
Other current assets	$ 51,055	$ 44,150
Fair value measurements on recurring basis | Total
Fair value of assets and liabilities
Other current assets	14,746
Total assets	14,746
Fair value measurements on recurring basis | Total | Level 1
Fair value of assets and liabilities
Other current assets	14,746
Total assets	14,746
Fair value measurements on recurring basis | Total | Level 2
Fair value of assets and liabilities
Other current assets	0
Total assets	0
Fair value measurements on recurring basis | Total | Level 3
Fair value of assets and liabilities
Other current assets	0
Total assets	$ 0