Consolidated Statements Of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Statement [Abstract]
Income (Loss) from Continuing Operations Attributable to Parent	$ 119,817	$ 104,273	$ 76,719
Operating Revenues:
Utility revenues	1,433,343	1,402,195	1,352,385
Non-utility revenues	39,219	39,549	38,953
Total operating revenues	1,472,562	1,441,744	1,391,338
Utility operating expenses:
Resource costs	678,244	689,586	693,127
Other operating expenses	286,832	276,228	276,780
Depreciation and amortization	129,570	117,174	112,091
Taxes other than income taxes	94,300	88,435	83,409
Non-utility operating expenses:
Other operating expenses	30,418	38,651	38,041
Depreciation and amortization	610	581	792
Total operating expenses	1,219,974	1,210,655	1,204,240
Income from continuing operations	252,588	231,089	187,098
Interest expense	75,302	77,118	75,104
Interest expense to affiliated trusts	450	467	541
Capitalized interest	(3,924)	(3,676)	(2,401)
Other income-net	(11,346)	(5,167)	(2,713)
Income from continuing operations before income taxes	192,106	162,347	116,567
Income tax expense	72,240	58,014	39,764
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest	119,866	104,333	76,803
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	72,224	6,804	1,491
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	72,411	7,961	1,997
Net income from continuing operations	192,277	112,294	78,800
Net income attributable to noncontrolling interests	(236)	(1,217)	(590)
Net income attributable to Avista Corporation shareholders	$ 192,041	$ 111,077	$ 78,210
Weighted-average common shares outstanding (thousands), basic	61,632	59,960	59,028
Weighted-average common shares outstanding (thousands), diluted	61,887	59,997	59,201
Income (Loss) from Continuing Operations, Per Basic Share	$ 1.94	$ 1.74	$ 1.30
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share	$ 1.18	$ 0.11	$ 0.02
Earnings per common share attributable to Avista Corporation shareholders:
Basic	$ 3.12	$ 1.85	$ 1.32
Diluted (usd per share)	$ 3.10	$ 1.85	$ 1.32
Income (Loss) from Continuing Operations, Per Diluted Share	$ 1.93	$ 1.74	$ 1.30
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share	$ 1.17	$ 0.11	$ 0.02