Regulatory Matters - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Regulated Asset Liability [Line Items]
Threshold limit of deadband and sharing bands for future surcharge or rebate to customer	$ 4,000,000.0
Company share of benefit (expense) under washington energy recovery mechanism	6,200,000	$ 4,400,000
Threshold to return washington energy recovery mechanism dollars to customers	$ 30,000,000
Proposed cumulative rebate refund period	2 years
Deferred natural gas costs, asset	$ 1,400,000
Deferred natural gas costs, liability		3,200,000
WASHINGTON
Regulated Asset Liability [Line Items]
Decoupling maximum rate increase request	3.00%
IDAHO | Power Deferrals Regulatory Asset [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	$ 2,500,000	300,000
Power Deferrals Regulatory Liability [Member] | WASHINGTON
Regulated Asset Liability [Line Items]
Regulatory liabilities	37,900,000	37,000,000.0
Revenue Subject to Refund [Member] | WASHINGTON
Regulated Asset Liability [Line Items]
Regulatory liabilities	0	0
Revenue Subject to Refund [Member] | IDAHO
Regulated Asset Liability [Line Items]
Regulatory liabilities	686,000	686,000
Revenue Subject to Refund [Member] | OREGON
Regulated Asset Liability [Line Items]
Regulatory liabilities	$ 0	$ 0