Consolidated Statements Of Equity And Redeemable Noncontrolling Interests - USD ($) $ in Thousands	Total	Common Stock [Member]	AOCI Attributable to Parent [Member]	Retained Earnings [Member]	Noncontrolling Interests [Member]
Beginning Balance (in shares) at Dec. 31, 2016		64,187,934
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares issued		198,218
Ending Balance (in shares) at Mar. 31, 2017		64,386,152
Beginning Balance at Dec. 31, 2016		$ 1,075,281	$ (7,568)	$ 581,014
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Equity compensation expense		922
Issuance of common stock, net of issuance costs		315
Payment of minimum tax withholdings for share-based payment awards		(3,420)
Other comprehensive income	$ 183		183
Reclassification of excess income tax benefits			0	0
Net income attributable to Avista Corporation shareholders	62,116			62,116
Cash dividends paid (common stock)				(23,167)
Ending Balance at Mar. 31, 2017	1,685,446	$ 1,073,098	(7,385)	619,963
Beginning Balance Noncontrolling Interest at Dec. 31, 2016					$ (251)
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Net income attributable to noncontrolling interests					21
Cash dividends paid to subsidiary noncontrolling interests					0
Ending Balance Noncontrolling Interest at Mar. 31, 2017					(230)
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Total Avista Corporation shareholders’ equity	1,685,676
Total Avista Corporation shareholders’ equity	$ 1,729,828
Beginning Balance (in shares) at Dec. 31, 2017	65,494,333	65,494,333
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares issued		174,144
Ending Balance (in shares) at Mar. 31, 2018	65,668,477	65,668,477
Beginning Balance at Dec. 31, 2017	$ 1,730,484	$ 1,133,448	(8,090)	604,470
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Equity compensation expense		1,798
Issuance of common stock, net of issuance costs		232
Payment of minimum tax withholdings for share-based payment awards		(3,929)
Other comprehensive income	204		204
Reclassification of excess income tax benefits			(1,742)	1,742
Net income attributable to Avista Corporation shareholders	54,890			54,890
Cash dividends paid (common stock)				(24,634)
Ending Balance at Mar. 31, 2018	1,758,571	$ 1,131,549	$ (9,628)	$ 636,468
Beginning Balance Noncontrolling Interest at Dec. 31, 2017	656				656
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Net income attributable to noncontrolling interests					66
Cash dividends paid to subsidiary noncontrolling interests					(540)
Ending Balance Noncontrolling Interest at Mar. 31, 2018	182				$ 182
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Total Avista Corporation shareholders’ equity	$ 1,758,389