Regulatory Matters (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Regulated Asset Liability [Line Items]
Company Share of Benefit (Expense) Under Washington Energy Recovery Mechanism	$ 4,400	$ 6,100
Threshold to Return Washington Energy Recovery Mechanism Dollars to Customers	30,000
Deferred natural gas costs	$ 3,200	40,700
WASHINGTON
Regulated Asset Liability [Line Items]
Decoupling Maximum Rate Increase Request	3.00%
Power Deferrals [Member] | WASHINGTON
Regulated Asset Liability [Line Items]
Regulatory Liabilities	$ (37,000)	(34,400)
Power Deferrals [Member] | IDAHO
Regulated Asset Liability [Line Items]
Regulatory Liabilities		(7,600)
Revenue Subject to Refund [Member] | WASHINGTON
Regulated Asset Liability [Line Items]
Regulatory Liabilities	0	(693)
Revenue Subject to Refund [Member] | IDAHO
Regulated Asset Liability [Line Items]
Regulatory Liabilities	$ (686)	$ (774)