Consolidated Statements Of Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	AOCI Attributable to Parent [Member]	Retained Earnings [Member]	Noncontrolling Interests [Member]
Common Stock, Dividends, Per Share, Cash Paid	$ 0.7450
Beginning Balance (in shares) at Dec. 31, 2017		65,494,333
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares issued		193,159
Ending Balance (in shares) at Jun. 30, 2018		65,687,492
Beginning Balance at Dec. 31, 2017		$ 1,133,448	$ (8,090)	$ 604,470
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Equity compensation expense		3,558
Issuance of common stock, net of issuance costs		1,227
Payment of minimum tax withholdings for share-based payment awards		(3,929)
Other comprehensive income	$ 408		408
Reclassification of excess income tax benefits			(1,742)	1,742
Net income attributable to Avista Corporation shareholders	80,467			80,467
Cash dividends paid (common stock)				(49,101)
Ending Balance at Jun. 30, 2018	$ 1,762,707	$ 1,134,304	(9,424)	637,578
Beginning Balance Noncontrolling Interest at Dec. 31, 2017					$ 656
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Net income (loss) attributable to noncontrolling interests					133
Cash dividends paid to subsidiary noncontrolling interests					(540)
Deconsolidation of noncontrolling interests related to sale of METALfx					0
Ending Balance Noncontrolling Interest at Jun. 30, 2018					249
Common Stock, Dividends, Per Share, Cash Paid	$ 0.3725
Beginning Balance (in shares) at Mar. 31, 2018		65,668,477
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares issued		19,015
Ending Balance (in shares) at Jun. 30, 2018		65,687,492
Beginning Balance at Mar. 31, 2018		$ 1,131,549	(9,628)	636,468
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Equity compensation expense		1,760
Issuance of common stock, net of issuance costs		995
Payment of minimum tax withholdings for share-based payment awards		0
Other comprehensive income	$ 204		204
Reclassification of excess income tax benefits			0	0
Net income attributable to Avista Corporation shareholders	25,577			25,577
Cash dividends paid (common stock)				(24,467)
Ending Balance at Jun. 30, 2018	1,762,707	$ 1,134,304	(9,424)	637,578
Beginning Balance Noncontrolling Interest at Mar. 31, 2018					182
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Net income (loss) attributable to noncontrolling interests					67
Cash dividends paid to subsidiary noncontrolling interests					0
Deconsolidation of noncontrolling interests related to sale of METALfx					0
Ending Balance Noncontrolling Interest at Jun. 30, 2018					249
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Total Avista Corporation shareholders’ equity	1,762,458
Total Avista Corporation shareholders’ equity	$ 1,773,220
Common Stock, Dividends, Per Share, Cash Paid	$ 0.7750
Beginning Balance (in shares) at Dec. 31, 2018	65,688,356	65,688,356
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares issued		422,961
Ending Balance (in shares) at Jun. 30, 2019	66,111,317	66,111,317
Beginning Balance at Dec. 31, 2018	$ 1,774,045	$ 1,136,491	(7,866)	644,595
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Equity compensation expense		6,495
Issuance of common stock, net of issuance costs		14,929
Payment of minimum tax withholdings for share-based payment awards		(891)
Other comprehensive income	321		321
Reclassification of excess income tax benefits			0	0
Net income attributable to Avista Corporation shareholders	141,113			141,113
Cash dividends paid (common stock)				(51,153)
Ending Balance at Jun. 30, 2019	1,884,034	$ 1,157,024	(7,545)	734,555
Beginning Balance Noncontrolling Interest at Dec. 31, 2018	825				825
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Net income (loss) attributable to noncontrolling interests					(216)
Cash dividends paid to subsidiary noncontrolling interests					0
Deconsolidation of noncontrolling interests related to sale of METALfx					(609)
Ending Balance Noncontrolling Interest at Jun. 30, 2019	$ 0				0
Common Stock, Dividends, Per Share, Cash Paid	$ 0.3875
Beginning Balance (in shares) at Mar. 31, 2019		65,749,932
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares issued		361,385
Ending Balance (in shares) at Jun. 30, 2019	66,111,317	66,111,317
Beginning Balance at Mar. 31, 2019		$ 1,140,242	(7,706)	734,774
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Equity compensation expense		2,043
Issuance of common stock, net of issuance costs		14,739
Payment of minimum tax withholdings for share-based payment awards		0
Other comprehensive income	$ 161		161
Reclassification of excess income tax benefits			0	0
Net income attributable to Avista Corporation shareholders	25,319			25,319
Cash dividends paid (common stock)				(25,538)
Ending Balance at Jun. 30, 2019	1,884,034	$ 1,157,024	$ (7,545)	$ 734,555
Beginning Balance Noncontrolling Interest at Mar. 31, 2019					912
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Net income (loss) attributable to noncontrolling interests					(303)
Cash dividends paid to subsidiary noncontrolling interests					0
Deconsolidation of noncontrolling interests related to sale of METALfx					(609)
Ending Balance Noncontrolling Interest at Jun. 30, 2019	0				$ 0
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Total Avista Corporation shareholders’ equity	$ 1,884,034