Summary Of Significant Accounting Policies Summary of Significant Accounting Policies (Operating Leases) (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Operating Leased Assets [Line Items]
Operating Leases, Future Minimum Payments, Remainder of Fiscal Year	$ 4,995
Operating Leases, Future Minimum Payments, Due in Two Years	4,876
Operating Leases, Future Minimum Payments, Due in Three Years	4,859
Operating Leases, Future Minimum Payments, Due in Four Years	4,782
Operating Leases, Future Minimum Payments, Due in Five Years	4,780
Operating Leases, Future Minimum Payments, Due Thereafter	102,389
Operating Leases, Future Minimum Payments Due	126,681
Avista Utilities [Member]
Operating Leased Assets [Line Items]
Operating Leases, Future Minimum Payments, Remainder of Fiscal Year	4,504
Operating Leases, Future Minimum Payments, Due in Two Years	4,394
Operating Leases, Future Minimum Payments, Due in Three Years	4,369
Operating Leases, Future Minimum Payments, Due in Four Years	4,292
Operating Leases, Future Minimum Payments, Due in Five Years	4,290
Operating Leases, Future Minimum Payments, Due Thereafter	98,962
Operating Leases, Future Minimum Payments Due	120,811
Corporate and Other [Member]
Operating Leased Assets [Line Items]
Operating Leases, Future Minimum Payments, Remainder of Fiscal Year	491
Operating Leases, Future Minimum Payments, Due in Two Years	482
Operating Leases, Future Minimum Payments, Due in Three Years	490
Operating Leases, Future Minimum Payments, Due in Four Years	490
Operating Leases, Future Minimum Payments, Due in Five Years	490
Operating Leases, Future Minimum Payments, Due Thereafter	3,427
Operating Leases, Future Minimum Payments Due	$ 5,870
Minimum [Member]
Operating Leased Assets [Line Items]
Lessee, Operating Lease, Term of Contract	1 year
Maximum [Member]
Operating Leased Assets [Line Items]
Lessee, Operating Lease, Term of Contract	45 years