OTHER ACCRUED EXPENSES: (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Mar. 31, 2020
Lessee, Lease, Description [Line Items]
Liabilities of non-qualified retirement plan	$ 14,793	$ 11,623
PDP performance plan liability (see Note 6)	10,839	16,318
DPM consideration holdback (see Note 6)	0	6,185
Other miscellaneous accrued expenses	23,383	25,224
Other accrued expenses	58,532	68,991
Accrued Liabilities
Lessee, Lease, Description [Line Items]
Short-term lease liabilities (see Note 4)	$ 9,517	$ 9,641