Debt (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Debt Instruments [Abstract]
Long-term Debt, Gross	$ 741,813	$ 786,700
Long-Term Debt, Current Maturities, Gross	30,000	97,000
Long-term Debt, Excluding Current Maturities, Gross	711,813	689,700
Debt Outstanding
Proceeds from Issuance of Debt		100,000
Short-term Debt, Other Disclosures [Abstract]
Short-term debt	217,620	54,200
Bank Loans	$ 0	$ 0
Short-term Debt, Weighted Average Interest Rate, at Point in Time	3.00%	1.90%
Commercial Paper, Maximum Maturity	46 days
Commercial Paper, Average Maturity	22 days
Letters of Credit Outstanding, Amount	$ 2,800
Liabilities, Fair Value Disclosure [Abstract]
Long-term Debt, Gross	741,813	$ 786,700
Note 4110 Series Due 2048 [Member]
Debt Outstanding
Proceeds from Issuance of Debt	$ 50,000
Debt Instrument, Interest Rate, Stated Percentage	4.11%
Note 1545 Series Due 2018 [Member]
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	1.55%
Repayments of Long-term Debt [Abstract]
Extinguishment of Debt, Amount	$ 75,000
Note 6600 Series B Due 2018 [Member]
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	6.60%
Repayments of Long-term Debt [Abstract]
Extinguishment of Debt, Amount	$ 22,000
Note 2822 Series Due 2027 [Member] [Domain]
Debt Outstanding
Proceeds from Issuance of Debt		$ 25,000
Debt Instrument, Interest Rate, Stated Percentage		2.822%
Note 3685 Series Due 2047 [Member] [Domain]
Debt Outstanding
Proceeds from Issuance of Debt		$ 75,000
Debt Instrument, Interest Rate, Stated Percentage		3.685%
Note 7000 Series Due 2017 [Member]
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage		7.00%
Repayments of Long-term Debt [Abstract]
Extinguishment of Debt, Amount		$ 40,000
Line of Credit [Member]
Short-term Debt, Other Disclosures [Abstract]
Line of Credit Facility, Maximum Borrowing Capacity	100,000
Line of Credit Facility Contingent Increase To Maximum Borrowing Capacity	150,000
Line of Credit Facility, Amount Outstanding	$ 0	0
Debt Instrument Covenant Consolidated Indebtedness To Capitalization Ratio	70.00%
Letter of Credit [Member]
Short-term Debt, Other Disclosures [Abstract]
Line of Credit Facility, Maximum Borrowing Capacity	$ 40,000
Letters of Credit Outstanding, Amount	0	0
Northwest Holdings Other [Member]
Debt Instruments [Abstract]
Long-term Debt, Gross	2,113	0
Liabilities, Fair Value Disclosure [Abstract]
Long-term Debt, Gross	2,113	0
Northwest Natural Gas Company [Member]
Debt Instruments [Abstract]
Long-term Debt, Gross	739,700	786,700
Long-Term Debt, Current Maturities, Gross	30,000	97,000
Long-term Debt, Excluding Current Maturities, Gross	709,700	689,700
Liabilities, Fair Value Disclosure [Abstract]
Long-term Debt, Gross	739,700	786,700
Unamortized Debt Issuance Expense	5,577	6,813
Long-term Debt	734,123	779,887
Debt Instrument, Fair Value Disclosure	760,222	853,339
Northwest Natural Gas Company [Member] \| Note 4110 Series Due 2048 [Member]
Debt Instruments [Abstract]
Secured Debt	$ 50,000	0
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	4.11%
Northwest Natural Gas Company [Member] \| Note 1545 Series Due 2018 [Member]
Debt Instruments [Abstract]
Secured Debt	$ 0	$ 75,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage		1.55%
Northwest Natural Gas Company [Member] \| Note 6600 Series B Due 2018 [Member]
Debt Instruments [Abstract]
Secured Debt	0	$ 22,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage		6.60%
Northwest Natural Gas Company [Member] \| Note 8310 Series B Due 2019 [Member]
Debt Instruments [Abstract]
Secured Debt	$ 10,000	$ 10,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	8.31%	8.31%
Northwest Natural Gas Company [Member] \| Note 7630 Series B Due 2019 [Member]
Debt Instruments [Abstract]
Secured Debt	$ 20,000	$ 20,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	7.63%	7.63%
Northwest Natural Gas Company [Member] \| Note 5370 Series B Due 2020 [Member]
Debt Instruments [Abstract]
Secured Debt	$ 75,000	$ 75,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	5.37%	5.37%
Northwest Natural Gas Company [Member] \| Note 9050 Series A Due 2021 [Member]
Debt Instruments [Abstract]
Secured Debt	$ 10,000	$ 10,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	9.05%	9.05%
Northwest Natural Gas Company [Member] \| Note 3176 Series B Due 2021 [Member]
Debt Instruments [Abstract]
Secured Debt	$ 50,000	$ 50,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	3.18%	3.18%
Northwest Natural Gas Company [Member] \| Note 3542 Series B Due 2023 [Member]
Debt Instruments [Abstract]
Secured Debt	$ 50,000	$ 50,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	3.54%	3.54%
Northwest Natural Gas Company [Member] \| Note 5620 Series B Due 2023 [Member]
Debt Instruments [Abstract]
Secured Debt	$ 40,000	$ 40,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	5.62%	5.62%
Northwest Natural Gas Company [Member] \| Note 7720 Series B Due 2025 [Member]
Debt Instruments [Abstract]
Secured Debt	$ 20,000	$ 20,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	7.72%	7.72%
Northwest Natural Gas Company [Member] \| Note 6520 Series B Due 2025 [Member]
Debt Instruments [Abstract]
Secured Debt	$ 10,000	$ 10,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	6.52%	6.52%
Northwest Natural Gas Company [Member] \| Note 7050 Series B Due 2026 [Member]
Debt Instruments [Abstract]
Secured Debt	$ 20,000	$ 20,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	7.05%	7.05%
Northwest Natural Gas Company [Member] \| Note 3211 Series B Due 2026 [Member]
Debt Instruments [Abstract]
Secured Debt	$ 35,000	$ 35,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	3.21%	3.21%
Northwest Natural Gas Company [Member] \| Note 2822 Series Due 2027 [Member]
Debt Instruments [Abstract]
Secured Debt	$ 25,000	$ 25,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	2.82%	2.82%
Northwest Natural Gas Company [Member] \| Note 7000 Series Due 2027 [Member]
Debt Instruments [Abstract]
Secured Debt	$ 20,000	$ 20,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	7.00%	7.00%
Northwest Natural Gas Company [Member] \| Note 6650 Series Due 2027 [Member]
Debt Instruments [Abstract]
Secured Debt	$ 19,700	$ 19,700
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	6.65%	6.65%
Northwest Natural Gas Company [Member] \| Note 6650 Series Due 2028 [Member]
Debt Instruments [Abstract]
Secured Debt	$ 10,000	$ 10,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	6.65%	6.65%
Northwest Natural Gas Company [Member] \| Note 7740 Series Due 2030 [Member]
Debt Instruments [Abstract]
Secured Debt	$ 20,000	$ 20,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	7.74%	7.74%
Northwest Natural Gas Company [Member] \| Note 7850 Series Due 2030 [Member]
Debt Instruments [Abstract]
Secured Debt	$ 10,000	$ 10,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	7.85%	7.85%
Northwest Natural Gas Company [Member] \| Note 5820 Series Due 2032 [Member]
Debt Instruments [Abstract]
Secured Debt	$ 30,000	$ 30,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	5.82%	5.82%
Northwest Natural Gas Company [Member] \| Note 5660 Series Due 2032 [Member]
Debt Instruments [Abstract]
Secured Debt	$ 40,000	$ 40,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	5.66%	5.66%
Northwest Natural Gas Company [Member] \| Note 5250 Series Due 2035 [Member]
Debt Instruments [Abstract]
Secured Debt	$ 10,000	$ 10,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	5.25%	5.25%
Northwest Natural Gas Company [Member] \| Note 4000 Series Due 2042 [Member]
Debt Instruments [Abstract]
Secured Debt	$ 50,000	$ 50,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	4.00%	4.00%
Northwest Natural Gas Company [Member] \| Note 3685 Series Due 2047 [Member]
Debt Instruments [Abstract]
Secured Debt	$ 75,000	$ 75,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	3.69%	3.69%
Northwest Natural Gas Company [Member] \| Note 4136 Series Due 2046 [Member]
Debt Instruments [Abstract]
Secured Debt	$ 40,000	$ 40,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	4.14%	4.14%
Northwest Natural Gas Company [Member]
Maturities of Long-term Debt [Abstract]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 30,000
Long-term Debt, Maturities, Repayments of Principal in Year Two	75,000
Long-term Debt, Maturities, Repayments of Principal in Year Three	60,000
Long-term Debt, Maturities, Repayments of Principal in Year Four	0
Long-term Debt, Maturities, Repayments of Principal in Year Five	90,000
Long-term Debt, Maturities, Repayments of Principal after Year Five	484,700
Short-term Debt, Other Disclosures [Abstract]
Short-term debt	217,500	$ 54,200
Northwest Natural Gas Company [Member] \| Line of Credit [Member]
Short-term Debt, Other Disclosures [Abstract]
Line of Credit Facility, Maximum Borrowing Capacity	300,000
Line of Credit Facility Contingent Increase To Maximum Borrowing Capacity	450,000
Line of Credit Facility, Amount Outstanding	$ 0
Debt Instrument Covenant Consolidated Indebtedness To Capitalization Ratio	70.00%
Northwest Natural Gas Company [Member] \| Letter of Credit [Member]
Short-term Debt, Other Disclosures [Abstract]
Line of Credit Facility, Maximum Borrowing Capacity	$ 60,000
Letters of Credit Outstanding, Amount	$ 0

Commercial Paper, Average Maturity (duration)

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Commercial Paper, Maximum Maturity (duration)

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Represents the maximum ratio of consolidated indebtedness to total capitalizationwhich is necessary to be maintained under the terms of the line of credit facility.

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Increased maximum borrowing capacity under the credit facility which the reporting entity may request.

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Long-Term Debt, Current Maturities, Gross

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Long-term Debt, Excluding Current Maturities, Gross

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Amounts due on short-term bank loans secured by customers' securities on the balance sheet date.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Gross amount of debt extinguished.

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

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Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

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