Debt (details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Long-term Debt, Current and Noncurrent [Abstract]
Debt Instrument, Description	At March 31, 2014, our gas storage segment’s long-term debt consisted of $40 million of senior secured debt with a maturity date of November 30, 2016. This debt consists of $20 million of fixed rate debt with an interest rate of 7.75% and $20 million of variable interest rate debt, which currently has an interest rate of 7.00%. The debt is secured by all of the membership interests in Gill Ranch and is nonrecourse to NW Natural. The company expects to redeem the $20 million of variable interest rate debt during the second quarter of 2014 and have reclassified this portion of the debt to current on our balance sheet at March 31, 2014.
Long-term Debt, Maturities, Repayment Terms	At March 31, 2014, our utility's long-term debt, including current maturities, consisted of $701.7 million of first mortgage bonds (FMBs) with maturity dates ranging from 2014 through 2042, interest rates ranging from 3.176% to 9.05%, and a weighted-average coupon rate of 5.55%. We did not redeem any FMBs during the three months ended March 31, 2014.
Long-term Debt, Unclassified [Abstract]
Carrying Amount	$ 741,700	$ 741,700	$ 691,700
Estimated Fair Value	820,458	806,359	825,038
Short-term Debt [Abstract]
Short-term Debt	$ 32,600	$ 188,200	$ 130,750

Identification of the lender and information about a contractual promise to repay a short-term or long-term obligation, which includes borrowings under lines of credit, notes payable, commercial paper, bonds payable, debentures, and other contractual obligations for payment. This may include rationale for entering into the arrangement, significant terms of the arrangement, which may include amount, repayment terms, priority, collateral required, debt covenants, borrowing capacity, call features, participation rights, conversion provisions, sinking-fund requirements, voting rights, basis for conversion if convertible and remarketing provisions. The description may be provided for individual debt instruments, rational groupings of debt instruments, or by debt in total.

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Including the current and noncurrent portions, carrying value at the balance sheet date of a financial instrument used to receive debt funding on a regular basis with original maturities ranging from 5-10 years.

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- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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