LEASES: Lease Cost (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Mar. 31, 2020
Lessee, Lease, Description [Line Items]
Right-of-use asset (see Note 4)	$ 14,108	$ 17,830
Other Noncurrent Assets
Lessee, Lease, Description [Line Items]
Right-of-use asset (see Note 4)	14,100	17,800
Accrued Liabilities
Lessee, Lease, Description [Line Items]
Short-term lease liabilities (see Note 4)	9,517	9,641
Other Noncurrent Liabilities
Lessee, Lease, Description [Line Items]
Long-term lease liabilities	$ 7,300	$ 11,400