Information By Business Segments (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) Reportable_Segments	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments | Reportable_Segments			2
Operating revenues	$ 314,501	$ 318,838	$ 750,971	$ 737,011
Resource costs	102,751	109,815	268,337	271,534
Other operating expenses	89,051	84,947	169,714	166,551
Depreciation and amortization	42,800	39,870	84,973	79,250
Income from operations	56,097	61,591	171,483	167,676
Interest expense	23,870	21,472	47,600	42,883
Income taxes	13,051	16,710	46,395	47,055
Net income from continuing operations attributable to Avista Corp. shareholders	21,771	27,254	83,887	84,903
Payments to Acquire Other Property, Plant, and Equipment	91,085	93,983	177,883	182,980
Total assets	5,373,004		5,373,004		$ 5,309,755
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Resource costs	0	0	0	0
Other operating expenses	0	0	0	0
Depreciation and amortization	0	0	0	0
Income from operations	0	0	0	0
Interest expense	(27)	(34)	(41)	(97)
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	308,729	312,888	739,266	725,681
Resource costs	102,751	109,815	268,337	271,534
Other operating expenses	81,965	78,666	156,449	154,445
Depreciation and amortization	42,643	39,678	84,628	78,870
Income from operations	57,568	62,114	173,388	168,832
Interest expense	23,721	21,357	47,298	42,670
Income taxes	13,967	17,025	47,447	47,592
Net income from continuing operations attributable to Avista Corp. shareholders	23,446	27,829	85,738	85,777
Payments to Acquire Other Property, Plant, and Equipment	90,951	93,937	177,714	182,815
Total assets	5,313,248		5,313,248		5,249,325
Operating Segments [Member] | Avista Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	296,747	302,641	712,128	702,788
Resource costs	99,461	106,607	262,074	265,685
Other operating expenses	78,970	75,790	150,682	149,046
Depreciation and amortization	41,195	38,351	81,733	76,217
Income from operations	53,971	59,862	162,606	161,107
Interest expense	22,826	20,462	45,509	40,880
Income taxes	12,892	16,349	43,909	45,021
Net income from continuing operations attributable to Avista Corp. shareholders	21,765	26,771	80,204	81,758
Payments to Acquire Other Property, Plant, and Equipment	88,612	88,048	174,015	172,483
Total assets	5,034,778		5,034,778		4,975,555
Operating Segments [Member] | Alaska Electric Light & Power [Member]
Segment Reporting Information [Line Items]
Operating revenues	11,982	10,247	27,138	22,893
Resource costs	3,290	3,208	6,263	5,849
Other operating expenses	2,995	2,876	5,767	5,399
Depreciation and amortization	1,448	1,327	2,895	2,653
Income from operations	3,597	2,252	10,782	7,725
Interest expense	895	895	1,789	1,790
Income taxes	1,075	676	3,538	2,571
Net income from continuing operations attributable to Avista Corp. shareholders	1,681	1,058	5,534	4,019
Payments to Acquire Other Property, Plant, and Equipment	2,339	5,889	3,699	10,332
Total assets	278,470		278,470		273,770
Operating Segments [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	5,772	5,950	11,705	11,330
Resource costs	0	0	0	0
Other operating expenses	7,086	6,281	13,265	12,106
Depreciation and amortization	157	192	345	380
Income from operations	(1,471)	(523)	(1,905)	(1,156)
Interest expense	176	149	343	310
Income taxes	(916)	(315)	(1,052)	(537)
Net income from continuing operations attributable to Avista Corp. shareholders	(1,675)	(575)	(1,851)	(874)
Payments to Acquire Other Property, Plant, and Equipment	134	$ 46	169	$ 165
Total assets	$ 59,756		$ 59,756		$ 60,430