Consolidated Statements Of Equity - 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		226,638
Ending Balance (in shares) at Sep. 30, 2017		64,414,572
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		5,055
Issuance of common stock, net of issuance costs		1,490
Payment of minimum tax withholdings for share-based payment awards		(3,420)
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests		(1,191)			$ 891
Other comprehensive income	$ 548		548
Reclassification of excess income tax benefits			0	0
Net income attributable to Avista Corporation shareholders	88,338			88,338
Cash dividends paid (common stock)				(69,220)
Ending Balance at Sep. 30, 2017	1,670,946	$ 1,077,215	(7,020)	600,132
Beginning Balance Noncontrolling Interest at Dec. 31, 2016					(251)
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Net income (loss) attributable to noncontrolling interests					(21)
Ending Balance Noncontrolling Interest at Sep. 30, 2017					619
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Total Avista Corporation shareholders’ equity	1,670,327
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		193,667
Ending Balance (in shares) at Sep. 30, 2018	65,688,000	65,688,000
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		4,800
Issuance of common stock, net of issuance costs		1,224
Payment of minimum tax withholdings for share-based payment awards		(3,929)
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests		0			0
Other comprehensive income	612		612
Reclassification of excess income tax benefits			(1,742)	1,742
Net income attributable to Avista Corporation shareholders	90,586			90,586
Cash dividends paid (common stock)				(73,569)
Ending Balance at Sep. 30, 2018	1,750,351	$ 1,135,543	$ (9,220)	$ 623,229
Beginning Balance Noncontrolling Interest at Dec. 31, 2017	656				656
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Net income (loss) attributable to noncontrolling interests					143
Ending Balance Noncontrolling Interest at Sep. 30, 2018	799				$ 799
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Total Avista Corporation shareholders’ equity	$ 1,749,552