Consolidated Statements Of Equity And Redeemable Noncontrolling Interests - USD ($) $ in Thousands	Total	Common Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Noncontrolling Interests [Member]
Beginning Balance (in shares) at Dec. 31, 2014		62,243,374
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares issued		149,883
Shares repurchased		(89,400)
Ending Balance (in shares) at Sep. 30, 2015		62,303,857
Beginning Balance at Dec. 31, 2014		$ 999,960	$ (7,888)	$ 491,599
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Equity compensation expense		4,579
Issuance of common stock, net of issuance costs		1,397
Payment of minimum tax withholdings for share-based payment awards		(1,832)
Repurchase of common stock		(1,431)		(1,489)
Excess tax benefits		43
Other comprehensive income (loss)	$ 737		737
Net income attributable to Avista Corporation shareholders	84,706			84,706
Cash dividends paid (common stock)				(61,828)
Ending Balance at Sep. 30, 2015	1,508,553	$ 1,002,716	(7,151)	512,988
Beginning Balance Noncontrolling Interest at Dec. 31, 2014					$ (429)
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Net income attributable to noncontrolling interests					73
Ending Balance Noncontrolling Interest at Sep. 30, 2015					(356)
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Total equity	1,508,197
Total equity	$ 1,528,287
Beginning Balance (in shares) at Dec. 31, 2015	62,312,651	62,312,651
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares issued		1,869,836
Shares repurchased		0
Ending Balance (in shares) at Sep. 30, 2016	64,182,487	64,182,487
Beginning Balance at Dec. 31, 2015	$ 1,528,626	$ 1,004,336	(6,650)	530,940
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Equity compensation expense		5,462
Issuance of common stock, net of issuance costs		66,756
Payment of minimum tax withholdings for share-based payment awards		(3,073)
Repurchase of common stock		0		0
Excess tax benefits		0
Other comprehensive income (loss)	(949)		(949)
Net income attributable to Avista Corporation shareholders	97,137			97,137
Cash dividends paid (common stock)				(65,172)
Ending Balance at Sep. 30, 2016	1,628,787	$ 1,073,481	$ (7,599)	$ 562,905
Beginning Balance Noncontrolling Interest at Dec. 31, 2015	339				(339)
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Net income attributable to noncontrolling interests					76
Ending Balance Noncontrolling Interest at Sep. 30, 2016	263				$ (263)
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Total equity	$ 1,628,524