Business Acquisitions Pro Forma Operating Results (Details) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014
Business Acquisition [Line Items]
Revenues	$ 312,580,000	$ 307,488,000	$ 759,158,000	$ 747,987,000
Revenues	43,150,000	44,560,000	87,534,000	86,967,000
Business Acquisition, Pro Forma Revenue	367,512,000	362,699,000	871,238,000	858,257,000
Income (Loss) from Continuing Operations Attributable to Parent	31,254,000	24,212,000	78,730,000	65,432,000
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	69,617,000	1,445,000	70,640,000	2,566,000
Net income (loss) attributable to Avista Corporation	100,871,000	25,657,000	149,370,000	67,998,000
Business Acquisition, Pro Forma Net Income (Loss)	103,461,000	27,467,000	155,669,000	75,433,000
Weighted Average Basic Shares Outstanding, Pro Forma	64,684	64,437	64,653	64,426
Pro Forma Weighted Average Shares Outstanding, Diluted	64,963	64,462	64,816	64,454
Business Acquisition, Pro Forma Earnings Per Share, Basic	$ 1.60	$ 0.43	$ 2.41	$ 1.17
Business Acquisition, Pro Forma Earnings Per Share, Diluted	$ 1.59	$ 0.43	$ 2.40	$ 1.17
Alaska Energy Resources Company [Member]
Business Acquisition [Line Items]
Gain (Loss) on Disposition of Assets				2,300,000
Revenues	11,782,000	10,651,000	24,546,000	23,303,000
Business Combination, Acquisition Related Costs					2,300,000
Net income (loss) attributable to Avista Corporation	2,371,000	1,810,000	5,627,000	7,435,000
Acquisition-related Costs [Member] | Alaska Energy Resources Company [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs	$ 219,000	$ 0	$ 672,000	$ 0