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Long-Term Debt (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Long-Term Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Debt Instrument [Line Items]
Long-term Debt	$ 900,685	$ 900,685	$ 736,236	$ 809,594
Unamortized debt issuance costs	$ 6,072	$ 6,072	5,577	5,940
Ratio of Indebtedness to Net Capital	0.534	0.534
Northwest Natural Gas Company [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 863,628	$ 863,628	734,123	808,760
Unamortized debt issuance costs	$ 6,072	$ 6,072	$ 5,577	$ 5,940
Northwest Natural Gas Company [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Stated interest rate	2.822%	2.822%
Weighted average interest rate	4.745%	4.745%
Northwest Natural Gas Company [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Stated interest rate	9.05%	9.05%
Note 3869 Series Due 2049 [Member] \| Northwest Natural Gas Company [Member]
Debt Instrument [Line Items]
Stated interest rate	3.869%	3.869%
Proceeds from Issuance of Debt		$ 90,000
Note 3141 Series Due 2029 [Member] \| Northwest Natural Gas Company [Member]
Debt Instrument [Line Items]
Stated interest rate	3.141%	3.141%
Proceeds from Issuance of Debt		$ 50,000
Note 8310 Series Due 2019 [Member] \| Northwest Natural Gas Company [Member]
Debt Instrument [Line Items]
Stated interest rate	8.31%	8.31%
Repayments of Debt	$ 10,000
Two-year Term Loan Due 2021 [Member]
Debt Instrument [Line Items]
Stated interest rate	2.65%	2.65%
Proceeds from Issuance of Debt		$ 35,000
Debt Instrument, Covenant Description		requires NW Holdings to maintain a consolidated indebtedness to total capitalization ratio of 70% or less