Avista Utilities Regulatory Matters (Narrative) (Details) (USD $) In Millions, unless otherwise specified	0 Months Ended	12 Months Ended					12 Months Ended						0 Months Ended	1 Months Ended		0 Months Ended			12 Months Ended		1 Months Ended			0 Months Ended						1 Months Ended		0 Months Ended				1 Months Ended		0 Months Ended										12 Months Ended		0 Months Ended		12 Months Ended	0 Months Ended		12 Months Ended		0 Months Ended	12 Months Ended	0 Months Ended			12 Months Ended
	May 10, 2013	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012	Apr. 30, 2012	Mar. 30, 2007	Dec. 31, 2013 Maximum [Member]	Dec. 31, 2013 Minimum [Member]	Dec. 31, 2013 Four Million Deadband [Member]	Dec. 31, 2013 Higher by $4 million to $10 million [Member]	Dec. 31, 2013 Lower by $4 million to $10 million [Member]	Dec. 31, 2013 Higher or lower by over $10 million [Member]	Feb. 04, 2014 UTC [Member]	Dec. 31, 2012 UTC [Member]	Dec. 31, 2013 UTC [Member]	Dec. 26, 2012 UTC [Member] 2.0 Percent [Member]	Feb. 04, 2014 UTC [Member] 3.8 Percent [Member]	Feb. 04, 2014 UTC [Member] 8.1 Percent [Member]	Dec. 31, 2013 UTC [Member] 4.6 Percent [Member]	Dec. 31, 2013 UTC [Member] 2.4 Percent [Member]	Dec. 31, 2012 UTC [Member] 3.0 Percent [Member]	Dec. 31, 2012 UTC [Member] 0.9 Percent [Member]	Dec. 31, 2012 UTC [Member] 3.6 Percent [Member]	Feb. 04, 2014 UTC [Member] 1.1 Percent [Member]	Feb. 04, 2014 UTC [Member] 2.8 Percent [Member]	Feb. 04, 2014 UTC [Member] 1.7 Percent [Member]	Feb. 04, 2014 UTC [Member] 5.5 Percent [Member]	Dec. 26, 2012 UTC [Member] 2013 [Member] 2.0 Percent [Member]	Dec. 26, 2012 UTC [Member] 2014 [Member] 2.0 Percent [Member]	Dec. 31, 2012 UTC [Member] 2014 [Member] 3.0 Percent [Member]	Dec. 31, 2012 UTC [Member] 2013 [Member] 3.0 Percent [Member]	Mar. 28, 2013 IPUC [Member]	Dec. 31, 2013 IPUC [Member]	Dec. 31, 2012 IPUC [Member]	Mar. 30, 2007 IPUC [Member]	Sep. 30, 2011 IPUC [Member] 1.1 Percent [Member]	Sep. 30, 2011 IPUC [Member] 1.6 Percent [Member]	Mar. 28, 2013 IPUC [Member] 1.9 Percent [Member]	Mar. 28, 2013 IPUC [Member] 2013 And 2014 [Member] 2.0 Percent [Member]	Mar. 28, 2013 IPUC [Member] 2013 And 2014 [Member] 3.1 Percent [Member]	Mar. 28, 2013 IPUC [Member] April Twenty Thirteen [Member] 4.9 Percent [Member]	Mar. 28, 2013 IPUC [Member] October Twenty Thirteen [Member] 2.0 Percent [Member]	Mar. 28, 2013 IPUC [Member] October Twenty Thirteen [Member] 0.3 Percent [Member]	Mar. 28, 2013 IPUC [Member] October Twenty Thirteen [Member] 3.1 Percent [Member]	Jan. 21, 2014 O.P.U.C [Member]	Jan. 21, 2014 O.P.U.C [Member] February Twenty Fourteen [Member] 4.4 Percent [Member]	Jan. 21, 2014 O.P.U.C [Member] November Twenty Fourteen [Member] 1.55 Percent [Member]	Dec. 31, 2013 O.P.U.C [Member] Software and Software Development Costs [Member]	Dec. 31, 2013 O.P.U.C [Member] Gas Distribution Equipment [Member]	May 10, 2013 Bonneville Power Administration [Member]	May 10, 2013 WASHINGTON	Dec. 31, 2013 WASHINGTON	May 10, 2013 WASHINGTON Bonneville Power Administration [Member]	Mar. 28, 2013 IDAHO	Dec. 31, 2013 IDAHO	Dec. 31, 2012 IDAHO	Mar. 28, 2013 IDAHO Bonneville Power Administration [Member]	Dec. 31, 2013 OREGON	May 10, 2013 Monthly [Member] Bonneville Power Administration [Member]	May 10, 2013 Annual [Member] Bonneville Power Administration [Member]	May 10, 2013 Annual [Member] WASHINGTON Bonneville Power Administration [Member]	Dec. 31, 2013 Deferred Maintenance Costs [Member]	Dec. 31, 2013 Deferred Maintenance Costs [Member] UTC [Member]	Dec. 31, 2013 Deferred Maintenance Costs [Member] IPUC [Member]	Dec. 31, 2013 Percent [Member]	Dec. 31, 2013 Electric [Member]	Dec. 31, 2013 Natural Gas [Member]
Regulated Asset Liability [Line Items]
Total net deferred power costs																																																				$ 17.9			$ 5.1	$ 5.1
Power cost, deferral balance																												4.4	9.0										1.6	3.9
Public Utilities, Approved Return on Equity, Percentage														9.80%																		9.80%													9.65%
Excess Earnings Refund																																																																		(2.0)	(0.4)
Past Use of Transmission System Settlement																																																		11.7			7.6				4.1
Wind development project costs	4.3																																																		2.5			1.7
Past Use of Transmission System Settlement Less Wind Project Costs																																																					5.1
Public Utilities, Approved Equity Capital Structure, Percentage														47.00%																		50.00%													48.00%
Deadband amount		4.0
Annual power supply cost variances							10.0	4.0				10.0
Deferred for future surcharge or rebate to customers										50.00%	75.00%	90.00%																																											90.00%										50.00%
Expense or benefit to the company									100.00%	50.00%	25.00%	10.00%
Base rate trigger point, percentage, ERM modification			10.00%
Base rate trigger point, ERM modification			45		30
Natural gas cost deferrals and recovery percentage		100.00%																																																								100.00%
Natural gas cost deferrals and recovery percentage recovered		90.00%
Refundable gas costs		12.1		6.9
Public Utilities, Approved Rate Increase (Decrease), Percentage														7.64%		2.00%			4.60%	2.40%	3.00%	0.90%	3.60%													1.10%	1.60%	1.90%			4.90%	2.00%	0.30%	3.10%	7.47%	4.40%	1.55%
Public Utilities, Requested Rate Increase (Decrease), Percentage													10.10%				3.80%	8.10%						1.10%	2.80%	1.70%	5.50%
Decoupling Maximum Rate Increase Request													3.00%
Public Utilities, Requested Rate Increase (Decrease), Amount																	18.2	12.1
Public Utilities, Requested Return on Equity, Percentage													7.71%
Public Utilities, Requested Equity Capital Structure, Percentage													49.00%
Public Utilities, Approved Rate Increase (Decrease), Amount																			20.0	3.8		1.4	5.3							14.0	13.6					2.8	1.1				3.1	1.3		7.8		4.3	1.4
Public Utilities, Requested Capital Costs, Amount																																																6.5	2.0
Period of years with deferred costs amortized																																																														2016	four	3
Deferred operation and maintenance costs														4.0	3.1																		2.8	2.3
Ownership interest		15.00%				15.00%																													15.00%
Electrical Transmission Revenue																																																											0.3	3.2	2.1
Electric Transmission Revenue Credit	$ 4.2