Balance Sheet Components - Schedule of Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Regulated Asset Liability [Line Items]
Regulatory assets	$ 44,199	$ 43,783
Non-current regulatory assets	839,155	860,626
Regulatory liabilities	94,609	77,149
Non-current regulatory liabilities	846,873	861,515
Income Tax Related Liabilities [Member]
Regulated Asset Liability [Line Items]
Regulatory liabilities	73,207	56,331
Non-current regulatory liabilities	416,719	458,789
Energy Commodity Derivatives [Member]
Regulated Asset Liability [Line Items]
Regulatory liabilities	1,801	0
Non-current regulatory liabilities	522	0
Deferred Power Costs [Member]
Regulated Asset Liability [Line Items]
Regulatory liabilities	0	6,457
Non-current regulatory liabilities	6,610	5,434
Decoupling Rebate [Member]
Regulated Asset Liability [Line Items]
Regulatory liabilities	3,624	3,049
Non-current regulatory liabilities	16,330	6,259
Utility Plant Retirement Costs [Member]
Regulated Asset Liability [Line Items]
Regulatory liabilities	0	0
Non-current regulatory liabilities	357,367	350,190
Interest Rate Swaps [Member]
Regulated Asset Liability [Line Items]
Regulatory liabilities	0	0
Non-current regulatory liabilities	21,270	15,062
COVID-19 Deferrals [Member]
Regulated Asset Liability [Line Items]
Regulatory liabilities	0	0
Non-current regulatory liabilities	12,049	12,500
Other Regulatory Liabilities [Member]
Regulated Asset Liability [Line Items]
Regulatory liabilities	15,977	11,312
Non-current regulatory liabilities	16,006	13,281
Energy Commodity Derivatives [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	12,447
Non-current regulatory assets	0	2,938
Decoupling Surcharge [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	8,834	9,907
Non-current regulatory assets	3,793	14,625
Deferred Natural Gas Costs [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	29,647	14,095
Non-current regulatory assets	11,323	6,932
Deferred Power Costs [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	5,300	7,334
Non-current regulatory assets	1,059	3,501
Pension and Other Postretirement Benefit Plans [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	162,943	165,696
Interest Rate Swaps [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	189,347	199,754
Deferred Income Taxes [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	245,893	244,154
Settlement with Coeur d'Alene Tribe [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	38,368	38,926
AFUDC Above FERC Allowed Rate [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	50,328	48,455
Demand Side Management Programs [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	3,736	3,974
Utility Plant to be Abandoned [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	25,555	26,771
COVID-19 Deferrals [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	13,963	13,591
Unamortized Debt Repurchase Costs [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	6,434	6,768
Advanced Meter Infrastructure [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	34,194	36,008
Other Regulatory Assets [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	418	0
Non-current regulatory assets	$ 52,219	$ 48,533