Information By Business Segments (Details) $ in Thousands	3 Months Ended								9 Months Ended	12 Months Ended
	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Sep. 30, 2015 Reportable_Segments	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments | Reportable_Segments									2
Operating revenues	$ 387,305	$ 313,649	$ 337,332	$ 446,490	$ 411,846	$ 301,558	$ 312,580	$ 446,578		$ 1,484,776	$ 1,472,562	$ 1,441,744
Resource costs										656,964	678,244	689,586
Other operating expenses										332,747	317,250	314,879
Depreciation and amortization										144,194	130,180	117,755
Income from operations	70,367	35,912	57,360	89,575	66,753	32,762	62,731	90,342		253,214	252,588	231,089
Interest expense										80,441	75,752	77,585
Total income tax expense										67,449	72,240	58,014
Payments to Acquire Other Property, Plant, and Equipment										394,310	325,922	294,734
Total assets	4,906,649				4,700,971					4,906,649	4,700,971	4,011,533
Income (Loss) from Continuing Operations Attributable to Parent	33,859	$ 12,722	$ 25,050	$ 46,449	30,581	$ 10,506	$ 31,254	$ 47,476		118,080	119,817	104,273
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues										1,456,641	1,435,143	1,403,995
Resource costs										656,964	678,244	689,586
Other operating expenses										303,221	286,832	276,228
Depreciation and amortization										143,499	129,570	117,174
Income from operations										255,300	246,197	232,572
Interest expense										79,963	75,132	75,663
Total income tax expense										68,691	69,450	60,472
Payments to Acquire Other Property, Plant, and Equipment										393,425	325,516	294,363
Total assets	4,867,443				4,620,830					4,867,443	4,620,830	3,930,251
Income (Loss) from Continuing Operations Attributable to Parent										120,001	116,415	108,598
Operating Segments [Member] | Avista Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues										1,411,863	1,413,499	1,403,995
Resource costs										644,991	672,344	689,586
Other operating expenses										292,096	280,964	276,228
Depreciation and amortization										138,236	126,987	117,174
Income from operations										241,228	239,976	232,572
Interest expense										76,405	73,750	75,663
Total income tax expense										64,489	67,634	60,472
Payments to Acquire Other Property, Plant, and Equipment										381,174	323,931	294,363
Total assets	4,601,708				4,357,760					4,601,708	4,357,760	3,930,251
Income (Loss) from Continuing Operations Attributable to Parent										113,360	113,263	108,598
Operating Segments [Member] | Alaska Electric Light & Power [Member]
Segment Reporting Information [Line Items]
Operating revenues										44,778	21,644	0
Resource costs										11,973	5,900	0
Other operating expenses										11,125	5,868	0
Depreciation and amortization										5,263	2,583	0
Income from operations										14,072	6,221	0
Interest expense										3,558	1,382	0
Total income tax expense										4,202	1,816	0
Payments to Acquire Other Property, Plant, and Equipment										12,251	1,585	0
Total assets	265,735				263,070					265,735	263,070	0
Income (Loss) from Continuing Operations Attributable to Parent										6,641	3,152	0
Operating Segments [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating revenues										28,685	39,219	39,549
Resource costs										0	0	0
Other operating expenses										30,076	32,218	40,451
Depreciation and amortization										695	610	581
Income from operations										(2,086)	6,391	(1,483)
Interest expense										610	1,004	2,247
Total income tax expense										(1,242)	2,790	(2,458)
Payments to Acquire Other Property, Plant, and Equipment										885	406	371
Total assets	39,206				80,141					39,206	80,141	81,282
Income (Loss) from Continuing Operations Attributable to Parent										(1,921)	3,236	(4,650)
Operating Segments [Member] | Ecova [Member]
Segment Reporting Information [Line Items]
Total assets												339,600
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues										(550)	(1,800)	(1,800)
Resource costs										0	0	0
Other operating expenses										(550)	(1,800)	(1,800)
Depreciation and amortization										0	0	0
Income from operations										0	0	0
Interest expense										(132)	(384)	(325)
Total income tax expense										0	0	0
Payments to Acquire Other Property, Plant, and Equipment										0	0	0
Total assets	$ 0				$ 0					0	0	0
Income (Loss) from Continuing Operations Attributable to Parent										$ 0	$ 166	$ 325