CONDENSED CONSOLIDATED STATEMENTS OF EQUITY - USD ($) $ in Thousands	Total	Common Stock [Member]	Accumulated Other Comprehensive Loss [Member]	Retained Earnings [Member]	Noncontrolling Interests [Member]
Beginning Balance (in shares) at Dec. 31, 2018		65,688,356
Shares issued		1,020,633
Ending Balance (in shares) at Sep. 30, 2019		66,708,989
Beginning Balance at Dec. 31, 2018		$ 1,136,491	$ (7,866)	$ 644,595
Equity compensation expense		8,426
Issuance of common stock, net of issuance costs		42,899
Payment of minimum tax withholdings for share-based payment awards		(891)
Ending Balance at Sep. 30, 2019	$ 1,893,568	$ 1,186,925	(7,383)	714,026
Other comprehensive income	483		483
Net income attributable to Avista Corporation shareholders	146,203			146,203
Cash dividends paid on common stock				(76,772)
Beginning Balance Noncontrolling Interest at Dec. 31, 2018					$ 825
Net loss attributable to noncontrolling interests	(216)
Deconsolidation of noncontrolling interests related to sale of METALfx	$ (609)
Dividends declared per common share	$ 1.1625
Beginning Balance (in shares) at Jun. 30, 2019		66,111,317
Shares issued		597,672
Ending Balance (in shares) at Sep. 30, 2019		66,708,989
Beginning Balance at Jun. 30, 2019		$ 1,157,024	(7,545)	734,555
Equity compensation expense		1,931
Issuance of common stock, net of issuance costs		27,970
Ending Balance at Sep. 30, 2019	$ 1,893,568	$ 1,186,925	(7,383)	714,026
Other comprehensive income	162		162
Net income attributable to Avista Corporation shareholders	$ 5,090			5,090
Cash dividends paid on common stock				(25,619)
Dividends declared per common share	$ 0.3875
Total Avista Corporation shareholders’ equity	$ 1,893,568
Total Avista Corporation shareholders’ equity	$ 1,939,284
Beginning Balance (in shares) at Dec. 31, 2019	67,176,996	67,176,996
Shares issued		1,557,465
Ending Balance (in shares) at Sep. 30, 2020	68,734,461	68,734,461
Beginning Balance at Dec. 31, 2019		$ 1,210,741	(10,259)	738,802
Equity compensation expense		3,502
Issuance of common stock, net of issuance costs		53,356
Payment of minimum tax withholdings for share-based payment awards		(2,408)
Ending Balance at Sep. 30, 2020	$ 1,982,851	$ 1,265,191	(9,614)	727,274
Other comprehensive income	645		645
Net income attributable to Avista Corporation shareholders	$ 70,753			70,753
Cash dividends paid on common stock				(82,281)
Dividends declared per common share	$ 1.2150
Beginning Balance (in shares) at Jun. 30, 2020		67,913,265
Shares issued		821,196
Ending Balance (in shares) at Sep. 30, 2020	68,734,461	68,734,461
Beginning Balance at Jun. 30, 2020		$ 1,234,901	(9,834)	749,971
Equity compensation expense		824
Issuance of common stock, net of issuance costs		29,466
Ending Balance at Sep. 30, 2020	$ 1,982,851	$ 1,265,191	(9,614)	727,274
Other comprehensive income	220		$ 220
Net income attributable to Avista Corporation shareholders	$ 4,876			4,876
Cash dividends paid on common stock				$ (27,573)
Dividends declared per common share	$ 0.4050
Total Avista Corporation shareholders’ equity	$ 1,982,851