Common Stock - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Class Of Stock [Line Items]
Preferred stock, shares outstanding	0	0
Amount available for dividend distribution without affecting covenants	$ 311,800
Preferred stock, shares authorized	10,000,000
Proceeds from issuance of common stock	$ 72,200	$ 64,573	$ 1,207
Common stock, shares authorized	200,000,000	200,000,000
Common Stock [Member]
Class Of Stock [Line Items]
Shares issued through sales agency agreements	1,905,000	1,409,588
Issuance of common stock through sales agency agreements, net of issuance costs	$ 70,561	$ 63,571
Sales Agency Agreement [Member]
Class Of Stock [Line Items]
Common stock, shares authorized	3,200,000
Common stock shares authorized under sales agency agreements remaining shares authorized to sell	1,300,000
Avista Utilities [Member]
Class Of Stock [Line Items]
Regulatory restrictions, maximum debt to equity	35.00%