Common Stock Dividends Declared (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Dividend Restrictions [Line Items]
Maximum Dividends Allowed by Debt Covenants	$ 385.3
Maximum Dividends Allowed by Regulator Approval	$ 231.0
Dividends declared per common share	$ 1.32	$ 1.27	$ 1.22
Avista Utilities [Member]
Dividend Restrictions [Line Items]
Regulatory Restrictions, Maximum Debt to Equity	40.00%