Entity Tax Identification Number Entity Tax Identification Number Entity File Number Entity File Number Legal Entity [Axis] Legal Entity [Axis] Title of 12(b) Security Title of 12(b) Security Local Phone Number Local Phone Number Soliciting Material Soliciting Material Entity Address, Address Line One Entity Address, Address Line One Entity Address, Postal Zip Code Entity Address, Postal Zip Code Entity Registrant Name Entity Registrant Name Entity Address, State or Province Entity Address, State or Province Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Written Communications Written Communications Trading Symbol Trading Symbol City Area Code City Area Code Document and Entity Information [Abstract] Document and Entity Information [Abstract] General document and entity information Document Information [Table] Document Information [Table] Document Period End Date Document Period End Date Pre-commencement Issuer Tender Offer Pre-commencement Issuer Tender Offer Amendment Flag Amendment Flag Entity Address, City or Town Entity Address, City or Town Document [Domain] Document [Domain] Entity [Domain] Entity [Domain] Security Exchange Name Security Exchange Name Document Information, Document [Axis] Document Information, Document [Axis] Document Information [Line Items] Document Information [Line Items] Document Type Document Type Northwest Natural Gas Company [Member] Northwest Natural Gas Company [Member] Northwest Natural Gas Company [Member] Pre-commencement Tender Offer Pre-commencement Tender Offer Entity Central Index Key Entity Central Index Key Entity Emerging Growth Company Entity Emerging Growth Company