Information By Business Segments (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) Reportable_Segments	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments | Reportable_Segments			2
Operating revenues	$ 303,349	$ 313,649	$ 1,040,360	$ 1,097,471
Resource costs	118,737	138,210	390,271	488,886
Other operating expenses	81,916	80,777	248,467	243,523
Depreciation and amortization	40,433	36,481	119,683	106,791
Income from operations	39,594	35,912	207,270	182,847
Interest expense	21,796	20,071	64,679	60,066
Income taxes	7,606	6,115	54,661	47,378
Net income from continuing operations attributable to Avista Corp. shareholders	12,234	12,722	97,137	84,221
Payments to Acquire Other Property, Plant, and Equipment	105,362	95,397	288,342	273,653
Total assets	5,215,106		5,215,106		$ 4,906,649
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	(550)
Resource costs	0	0	0	0
Other operating expenses	0	0	0	(550)
Depreciation and amortization	0	0	0	0
Income from operations	0	0	0	0
Interest expense	(19)	(29)	(116)	(81)
Income taxes	0	0	0	0
Net income from continuing operations attributable to Avista Corp. shareholders	0	0	0	0
Payments to Acquire Other Property, Plant, and Equipment	0	0	0	0
Total assets	0		0		0
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	296,989	307,405	1,022,670	1,075,192
Resource costs	118,737	138,210	390,271	488,886
Other operating expenses	75,160	74,315	229,605	220,599
Depreciation and amortization	40,240	36,303	119,110	106,279
Income from operations	40,183	36,308	209,015	184,004
Interest expense	21,666	19,950	64,336	59,686
Income taxes	8,322	6,209	55,914	48,004
Net income from continuing operations attributable to Avista Corp. shareholders	13,539	12,919	99,316	85,340
Payments to Acquire Other Property, Plant, and Equipment	105,257	95,049	288,072	272,801
Total assets	5,159,679		5,159,679		4,867,443
Operating Segments [Member] | Avista Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	287,193	298,132	989,981	1,042,913
Resource costs	115,228	135,048	380,913	479,604
Other operating expenses	72,318	71,536	221,364	212,293
Depreciation and amortization	38,909	34,986	115,126	102,334
Income from operations	38,554	34,800	199,661	175,003
Interest expense	20,772	19,054	61,652	56,991
Income taxes	7,983	5,980	53,004	45,500
Net income from continuing operations attributable to Avista Corp. shareholders	12,673	12,525	94,431	81,387
Payments to Acquire Other Property, Plant, and Equipment	101,558	92,271	274,041	264,283
Total assets	4,889,256		4,889,256		4,601,708
Operating Segments [Member] | Alaska Electric Light & Power [Member]
Segment Reporting Information [Line Items]
Operating revenues	9,796	9,273	32,689	32,279
Resource costs	3,509	3,162	9,358	9,282
Other operating expenses	2,842	2,779	8,241	8,306
Depreciation and amortization	1,331	1,317	3,984	3,945
Income from operations	1,629	1,508	9,354	9,001
Interest expense	894	896	2,684	2,695
Income taxes	339	229	2,910	2,504
Net income from continuing operations attributable to Avista Corp. shareholders	866	394	4,885	3,953
Payments to Acquire Other Property, Plant, and Equipment	3,699	2,778	14,031	8,518
Total assets	270,423		270,423		265,735
Operating Segments [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	6,360	6,244	17,690	22,829
Resource costs	0	0	0	0
Other operating expenses	6,756	6,462	18,862	23,474
Depreciation and amortization	193	178	573	512
Income from operations	(589)	(396)	(1,745)	(1,157)
Interest expense	149	150	459	461
Income taxes	(716)	(94)	(1,253)	(626)
Net income from continuing operations attributable to Avista Corp. shareholders	(1,305)	(197)	(2,179)	(1,119)
Payments to Acquire Other Property, Plant, and Equipment	105	$ 348	270	$ 852
Total assets	$ 55,427		$ 55,427		$ 39,206