Regulatory Assets and Liabilities (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Regulatory Asset [Domain]
Regulatory Assets [Line Items]
Regulatory Assets	$ 145,746,000	$ 154,901,000
Asset Retirement Obligation [Member]
Regulatory Assets [Line Items]
Regulatory Assets	10,756,000	9,199,000
Debt Related Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	8,885,000	9,288,000
Deferred Pension And Other Postretirement Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	6,216,000	0
Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory Assets	26,875,000	31,830,000
Leases
Regulatory Assets [Line Items]
Regulatory Assets	2,400,000	59,000
Tax Recovery AFUDC Equity [Member]
Regulatory Assets [Line Items]
Regulatory Assets	7,060,000	6,482,000
Unfunded Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	83,214,000	96,030,000
Other Regulatory Asset [Member]
Regulatory Assets [Line Items]
Regulatory Assets	$ 340,000	$ 2,013,000