Summary of Significant Accounting Policies (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) employee	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Entity number of employees | employee	0
Public Utility, Property, Plant and Equipment [Line Items]
Regulatory Assets	$ 21,434	$ 22,913
Capitalized Interest Costs, Including Allowance for Funds Used During Construction [Abstract]
Allowance for funds used during construction, debt	300	700	$ 500
Allowance for funds used during construction, equity	400	2,700	1,700
Interest Payments [Abstract]
Cash payments for interest, net of interest capitalized	26,100	26,200	25,400
Levelized depreciation
Public Utility, Property, Plant and Equipment [Line Items]
regulatory debits	1,100	1,100	$ 2,300
Asset retirement obligation [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Regulatory Assets	$ 96,300	$ 90,900
Storage Facilities [Member] | Minimum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Depreciaton rates	1.60%	1.60%	1.60%
Storage Facilities [Member] | Maximum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Depreciaton rates	2.76%	2.76%	2.76%
Transmission Facilities [Member] | Minimum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Depreciaton rates	2.80%	2.80%	2.80%
Transmission Facilities [Member] | Maximum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Depreciaton rates	6.97%	6.97%	6.97%
Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lessee, Operating Lease, Term of Contract	38 years
Accounting Standards Update 2016-02 [Member] | Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lessee, Operating Lease, Term of Contract	1 year
Accounting Standards Update 2016-02 [Member] | Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lessee, Operating Lease, Term of Contract	15 years