Information By Business Segments (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) Reportable_Segments	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments | Reportable_Segments			2
Operating revenues	$ 318,838	$ 337,332	$ 737,011	$ 783,822
Resource costs	109,815	141,116	271,534	350,676
Other operating expenses	84,947	79,758	166,551	162,746
Depreciation and amortization	39,870	35,841	79,250	70,310
Income from operations	61,591	57,360	167,676	146,935
Interest expense	21,472	19,981	42,883	39,995
Income taxes	16,710	15,016	47,055	41,263
Net income from continuing operations attributable to Avista Corp. shareholders	27,254	25,050	84,903	71,499
Payments to Acquire Other Property, Plant, and Equipment	93,983	96,247	182,980	178,256
Total assets	5,069,021		5,069,021		$ 4,906,649
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	(100)	0	(550)
Resource costs	0	0	0	0
Other operating expenses	0	(100)	0	(550)
Depreciation and amortization	0	0	0	0
Income from operations	0	0	0	0
Interest expense	(34)	(30)	(97)	(52)
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	312,888	330,930	725,681	767,787
Resource costs	109,815	141,116	271,534	350,676
Other operating expenses	78,666	73,112	154,445	146,284
Depreciation and amortization	39,678	35,676	78,870	69,976
Income from operations	62,114	57,769	168,832	147,696
Interest expense	21,357	19,864	42,670	39,736
Income taxes	17,025	15,223	47,592	41,795
Net income from continuing operations attributable to Avista Corp. shareholders	27,829	25,403	85,777	72,421
Payments to Acquire Other Property, Plant, and Equipment	93,937	96,155	182,815	177,752
Total assets	5,014,706		5,014,706		4,867,443
Operating Segments [Member] | Avista Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	302,641	320,698	702,788	744,781
Resource costs	106,607	137,896	265,685	344,556
Other operating expenses	75,790	70,348	149,046	140,757
Depreciation and amortization	38,351	34,351	76,217	67,348
Income from operations	59,862	55,415	161,107	140,203
Interest expense	20,462	18,969	40,880	37,937
Income taxes	16,349	14,632	45,021	39,520
Net income from continuing operations attributable to Avista Corp. shareholders	26,771	24,478	81,758	68,862
Payments to Acquire Other Property, Plant, and Equipment	88,048	90,800	172,483	172,012
Total assets	4,742,362		4,742,362		4,601,708
Operating Segments [Member] | Alaska Electric Light & Power [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,247	10,232	22,893	23,006
Resource costs	3,208	3,220	5,849	6,120
Other operating expenses	2,876	2,764	5,399	5,527
Depreciation and amortization	1,327	1,325	2,653	2,628
Income from operations	2,252	2,354	7,725	7,493
Interest expense	895	895	1,790	1,799
Income taxes	676	591	2,571	2,275
Net income from continuing operations attributable to Avista Corp. shareholders	1,058	925	4,019	3,559
Payments to Acquire Other Property, Plant, and Equipment	5,889	5,355	10,332	5,740
Total assets	272,344		272,344		265,735
Operating Segments [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	5,950	6,502	11,330	16,585
Resource costs	0	0	0	0
Other operating expenses	6,281	6,746	12,106	17,012
Depreciation and amortization	192	165	380	334
Income from operations	(523)	(409)	(1,156)	(761)
Interest expense	149	147	310	311
Income taxes	(315)	(207)	(537)	(532)
Net income from continuing operations attributable to Avista Corp. shareholders	(575)	(353)	(874)	(922)
Payments to Acquire Other Property, Plant, and Equipment	46	$ 92	165	$ 504
Total assets	$ 54,315		$ 54,315		$ 39,206