Property, Plant And Equipment (Major Classifications Of Property, Plant And Equipment) (Details) (USD $)	Dec. 31, 2014		Dec. 31, 2013
Public Utility, Property, Plant and Equipment [Line Items]
Construction work-in-progress (CWIP) and other	$ 227,758,000		$ 160,323,000
Total	4,945,820,000		4,450,787,000
Other intangibles, property and investments-net	42,016,000		58,555,000
Total	4,971,623,000		4,502,784,000
Avista Utilities [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Total	4,750,468,000		4,450,787,000
Alaska Electric Light & Power [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Total	195,352,000		0
Ecova [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Other intangibles, property and investments-net	0	[1]	31,865,000	[1]
Accumulated depreciation			26,400,000
Other [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Other intangibles, property and investments-net	25,803,000	[1]	20,132,000	[1]
Accumulated depreciation	10,800,000		11,400,000
Electric [Member] | Avista Utilities [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Production	1,171,002,000		1,141,790,000
Transmission	603,909,000		569,056,000
Distribution	1,360,185,000		1,284,428,000
Construction work-in-progress (CWIP) and other	311,807,000		276,582,000
Total	3,446,903,000		3,271,856,000
Electric [Member] | Alaska Electric Light & Power [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Production	71,969,000		0
Transmission	18,392,000		0
Distribution	17,936,000		0
Public Utilities Property Plant And Equipment Capital Lease Assets	71,007,000		0
Construction work-in-progress (CWIP) and other	7,893,000		0
Total	187,197,000		0
Natural Gas [Member] | Avista Utilities [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Distribution	810,487,000		762,044,000
Construction work-in-progress (CWIP) and other	57,088,000		47,751,000
Natural gas underground storage	41,963,000		41,248,000
Total	909,538,000		851,043,000
Common Plant [Member] | Avista Utilities [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Total	394,027,000		327,888,000
Common Plant [Member] | Alaska Electric Light & Power [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Total	$ 8,155,000		$ 0

[1] Included in other property and investments-net on the Consolidated Balance Sheets. Ecova was sold on June 30, 2014; therefore, there is no property and equipment associated with them as of December 31, 2014. Accumulated depreciation was $26.4 million as of December 31, 2013 for Ecova. Accumulated depreciation was $10.8 million as of December 31, 2014 and $11.4 million as of December 31, 2013 for the other businesses. The decrease in accumulated depreciation for the other businesses was due to the sale of certain assets which were nearing the end of their useful lives during 2014.