Summary of Significant Accounting Policies (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) employee	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jan. 01, 2019 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, liability	$ 18,179
Operating Lease, Right-of-Use Asset	18,101	$ 0
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Regulatory charges resulting from tax rate changes	$ 23,580	35,680	$ 206,547
Entity number of employees | employee	0
Public Utility, Property, Plant and Equipment [Line Items]
Regulatory Assets	$ 22,913	31,025
Capitalized Interest Costs, Including Allowance for Funds Used During Construction [Abstract]
Allowance for funds used during construction, debt	700	500	300
Allowance for funds used during construction, equity	2,700	1,700	1,100
Interest Payments [Abstract]
Cash payments for interest, net of interest capitalized	26,200	25,400	31,900
Levelized depreciation
Public Utility, Property, Plant and Equipment [Line Items]
regulatory debit credits	1,100	2,300	$ 4,900
Asset retirement obligation [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Regulatory Assets	90,900	$ 86,400
Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent			21.00%
Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent			35.00%
Federal Tax [Member] [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Regulatory charges resulting from tax rate changes	206,500
State Tax [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Regulatory charges resulting from tax rate changes	$ 12,100
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
Operating lease, liability				$ 17,800
Operating Lease, Right-of-Use Asset				$ 17,800
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