FAIR VALUE OF FINANCIAL INSTRUMENTS: (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Mar. 31, 2020
Fair value of assets and liabilities
Assets of non-qualified retirement plan	$ 16,425	$ 11,623
Fair value measurements on recurring basis | Total
Fair value of assets and liabilities
Assets of non-qualified retirement plan	16,425	11,623
Total assets	16,425	11,623
Fair value measurements on recurring basis | Total | Level 1
Fair value of assets and liabilities
Assets of non-qualified retirement plan	16,425	11,623
Total assets	16,425	11,623
Fair value measurements on recurring basis | Total | Level 2
Fair value of assets and liabilities
Assets of non-qualified retirement plan	0	0
Total assets	0	0
Fair value measurements on recurring basis | Total | Level 3
Fair value of assets and liabilities
Assets of non-qualified retirement plan	0	0
Total assets	$ 0	$ 0