Common Stock Common Stock (Dividends Declared) (Details)	Dec. 31, 2018 USD ($) $ / shares
Dividend Restrictions [Line Items]
Amount Available For Dividend Distribution Without Affecting Covenants	$ 231,100,000
Maximum Dividend Increase Allowed Per Merger Agreement	$ 0.06
Maximum Dividend Allowed Per Merger Agreement | $ / shares	$ 1.49
Avista Utilities [Member]
Dividend Restrictions [Line Items]
Regulatory Restrictions, Maximum Debt to Equity	40.00%