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Sale of Stock, Offering Period

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Aggregate number of common shares reserved for future issuance.

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The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

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Number of options outstanding, including both vested and non-vested options.

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Price of a single share of a number of saleable stocks of a company.

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Number of new stock issued during the period.

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Equity impact of the value of new stock issued during the period. Includes shares issued in an initial public offering or a secondary public offering.

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Amount of stock repurchase plan authorized.

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The number of shares authorized to be repurchased by an entity's Board of Directors under a stock repurchase plan.

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Number of shares that have been repurchased during the period and are being held in treasury.

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Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method.

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Common Stock - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	12 Months Ended
	Nov. 16, 2016	Nov. 30, 2016	Dec. 31, 2018	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Authorized (in shares)			100,000,000		100,000,000
Issuance of common stock, net of issuance costs				$ 52,761
Restated Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number			55,938	180,163	91,688	352,688
Stock Repurchase Plan [Member]
Stock Repurchase Program
Stock Repurchase Program, Number of Shares Authorized to be Repurchased			2,800,000
Stock Repurchase Program, Authorized Amount			$ 100,000
Treasury Stock, Shares, Acquired			0
Repurchases Since Plan Inception in Year 2000 [Member] \| Stock Repurchase Plan [Member]
Stock Repurchase Program
Treasury Stock, Shares, Acquired			2,100,000
Treasury Stock, Value, Acquired, Cost Method			$ 83,300
Northwest Holdings [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reserved Shares Dividend Reinvestment			394,204
Northwest Holdings [Member] \| Employee Stock Purchase Plan Member [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock, Capital Shares Reserved for Future Issuance			24,339
Northwest Natural Gas Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Authorized (in shares)			100,000,000		100,000,000
Share Price	$ 54.63
Issuance of common stock, net of issuance costs	$ 52,800			$ 52,761
Northwest Natural Gas Company [Member] \| Base shares offered [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity Issuance		880,000
Northwest Natural Gas Company [Member] \| Over-Allotment Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity Issuance		132,000
Sale of Stock, Offering Period		30 days
Northwest Natural Gas Company [Member] \| Total shares issued [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity Issuance	1,012,000