CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 129,488	$ 196,763	$ 136,598
Other Comprehensive Income (Loss):
Change in unfunded benefit obligation for pension and other postretirement benefit plans - net of taxes of $(1,095), $(636) and $523, respectively	(4,119)	(2,393)	1,966
Total other comprehensive income (loss)	(4,119)	(2,393)	1,966
Comprehensive income	125,369	194,370	138,564
Comprehensive loss (income) attributable to noncontrolling interests		216	(169)
Comprehensive income attributable to Avista Corporation shareholders	$ 125,369	$ 194,586	$ 138,395