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]	Redeemable Noncontrolling Interests [Member]
Excess Tax Benefit from Share-based Compensation, Financing Activities		$ 3,936
Noncontrolling Interest in Net Income (Loss) Other Noncontrolling Interests, Redeemable						$ (4)
Noncontrolling Interest in Net Income (Loss) Other Noncontrolling Interests, Nonredeemable					$ 217
Noncontrolling Interest, Decrease from Deconsolidation	$ (23,612)
Beginning Balance (in shares) at Dec. 31, 2013		60,076,752
Issuance of common stock		4,685,953
Beginning Balance at Dec. 31, 2013		$ 896,993	$ (5,819)	$ 407,092	20,001	15,889
Equity compensation expense		6,061
Issuance of common stock, net of issuance costs		153,501
Adjustments Related to Tax Withholding for Share-based Compensation		0
Stock Repurchased During Period, Value		(30,794)		(30,169)
Equity transactions of consolidated subsidiaries		(1,062)
Payments for Repurchase of Redeemable Noncontrolling Interest	(20,871)	(20,871)
Other comprehensive loss	1,921		1,921
Net income attributable to Avista Corporation shareholders	159,821			159,821
Cash dividends paid (common stock)				(58,552)
Other					2,943
Purchase of subsidiary noncontrolling interests						(12)
Valuation adjustments and other noncontrolling interests activity				10,150		(15,873)
Ending Balance at Sep. 30, 2014	1,492,208	$ 1,007,764	(3,898)	488,342	(451)	0
Ending Balance (in shares) at Sep. 30, 2014		62,838,628
Stock Repurchased During Period, Shares		(1,924,077)
Total equity	1,491,757
Total equity	1,483,242
Excess Tax Benefit from Share-based Compensation, Financing Activities		$ 43
Noncontrolling Interest in Net Income (Loss) Other Noncontrolling Interests, Redeemable						0
Noncontrolling Interest in Net Income (Loss) Other Noncontrolling Interests, Nonredeemable					73
Noncontrolling Interest, Decrease from Deconsolidation	$ 0
Beginning Balance (in shares) at Dec. 31, 2014	62,243,374	62,243,374
Issuance of common stock		149,883
Beginning Balance at Dec. 31, 2014	$ 1,483,671	$ 999,960	(7,888)	491,599	(429)	0
Equity compensation expense		4,579
Issuance of common stock, net of issuance costs		1,397
Adjustments Related to Tax Withholding for Share-based Compensation		(1,832)
Stock Repurchased During Period, Value		(1,431)		(1,489)
Equity transactions of consolidated subsidiaries		0
Payments for Repurchase of Redeemable Noncontrolling Interest	0	0
Other comprehensive loss	737		737
Net income attributable to Avista Corporation shareholders	84,706			84,706
Cash dividends paid (common stock)				(61,828)
Other					0
Purchase of subsidiary noncontrolling interests						0
Valuation adjustments and other noncontrolling interests activity				0		0
Ending Balance at Sep. 30, 2015	$ 1,508,553	$ 1,002,716	$ (7,151)	$ 512,988	$ (356)	$ 0
Ending Balance (in shares) at Sep. 30, 2015	62,303,857	62,303,857
Stock Repurchased During Period, Shares	(89,400)	(89,400)
Total equity	$ 1,508,197