Balance Sheet Components - Schedule of Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Regulated Asset Liability [Line Items]
Regulatory Assets, Current	$ 163,906	$ 193,787
Regulatory Assets, Non-Current	861,491	833,328
Regulatory Liabilities, Current	79,093	95,665
Regulatory Liabilities, Non-Current	845,022	840,837
Income Tax Related Liabilities [Member]
Regulated Asset Liability [Line Items]
Regulatory Liabilities, Current	48,879	73,267
Regulatory Liabilities, Non-Current	365,954	390,734
Deferred Natural Gas Costs [Member]
Regulated Asset Liability [Line Items]
Regulatory Liabilities, Current	4,924	0
Regulatory Liabilities, Non-Current	0	0
Decoupling Rebate [Member]
Regulated Asset Liability [Line Items]
Regulatory Liabilities, Current	13,066	9,469
Regulatory Liabilities, Non-Current	26,798	20,476
Utility Plant Retirement Costs [Member]
Regulated Asset Liability [Line Items]
Regulatory Liabilities, Current	0	0
Regulatory Liabilities, Non-Current	403,291	376,817
Interest Rate Swaps [Member]
Regulated Asset Liability [Line Items]
Regulatory Liabilities, Current	0	0
Regulatory Liabilities, Non-Current	23,402	24,204
COVID-19 Deferrals [Member]
Regulated Asset Liability [Line Items]
Regulatory Liabilities, Current	0	0
Regulatory Liabilities, Non-Current	11,069	11,874
Other Regulatory Liabilities [Member]
Regulated Asset Liability [Line Items]
Regulatory Liabilities, Current	12,224	12,929
Regulatory Liabilities, Non-Current	14,508	16,732
Energy Commodity Derivatives [Member]
Regulated Asset Liability [Line Items]
Regulatory Assets, Current	41,198	112,090
Regulatory Assets, Non-Current	18,370	18,185
Decoupling Surcharge [Member]
Regulated Asset Liability [Line Items]
Regulatory Assets, Current	4,105	6,250
Regulatory Assets, Non-Current	3,129	5,449
Deferred Natural Gas Costs [Member]
Regulated Asset Liability [Line Items]
Regulatory Assets, Current	88,897	52,091
Regulatory Assets, Non-Current	0	0
Deferred Power Costs [Member]
Regulated Asset Liability [Line Items]
Regulatory Assets, Current	29,706	23,356
Regulatory Assets, Non-Current	20,527	24,043
Deferred Income Taxes [Member]
Regulated Asset Liability [Line Items]
Regulatory Assets, Current	0	0
Regulatory Assets, Non-Current	240,143	240,325
Pension and Other Postretirement Benefit Plans [Member]
Regulated Asset Liability [Line Items]
Regulatory Assets, Current	0	0
Regulatory Assets, Non-Current	132,530	135,337
Interest Rate Swaps [Member]
Regulated Asset Liability [Line Items]
Regulatory Assets, Current	0	0
Regulatory Assets, Non-Current	182,793	185,919
AFUDC Above FERC Allowed Rate [Member]
Regulated Asset Liability [Line Items]
Regulatory Assets, Current	0	0
Regulatory Assets, Non-Current	50,365	51,649
Settlement with Coeur d'Alene Tribe [Member]
Regulated Asset Liability [Line Items]
Regulatory Assets, Current	0	0
Regulatory Assets, Non-Current	37,251	37,809
Advanced Meter Infrastructure [Member]
Regulated Asset Liability [Line Items]
Regulatory Assets, Current	0	0
Regulatory Assets, Non-Current	30,863	32,381
Utility Plant Abandoned [Member]
Regulated Asset Liability [Line Items]
Regulatory Assets, Current	0	0
Regulatory Assets, Non-Current	30,563	24,389
Deferred Climate Commitment Act Costs [Member]
Regulated Asset Liability [Line Items]
Regulatory Assets, Current	0	0
Regulatory Assets, Non-Current	32,008	0
COVID-19 Deferrals [Member]
Regulated Asset Liability [Line Items]
Regulatory Assets, Current	0	0
Regulatory Assets, Non-Current	9,230	9,793
Unamortized Debt Repurchase Costs [Member]
Regulated Asset Liability [Line Items]
Regulatory Assets, Current	0	0
Regulatory Assets, Non-Current	5,934	6,177
Demand Side Management Programs [Member]
Regulated Asset Liability [Line Items]
Regulatory Assets, Current	0	0
Regulatory Assets, Non-Current	485	3,683
Other Regulatory Assets [Member]
Regulated Asset Liability [Line Items]
Regulatory Assets, Current	0	0
Regulatory Assets, Non-Current	$ 67,300	$ 58,189