Pension and Other Postretirement Benefits Costs - Schedule of Pension Plan Target Allocations (Details)	Dec. 31, 2018
Long government/credit [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation, percentage	20.00%
U.S. small/mid cap equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation, percentage	10.00%
Emerging markets equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation, percentage	5.00%
Northwest Natural Gas Company [Member] | U.S. large cap equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation, percentage	18.00%
Northwest Natural Gas Company [Member] | Non-U.S. equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation, percentage	18.00%
Northwest Natural Gas Company [Member] | Absolute Return Strategy Investment Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation, percentage	12.00%
Northwest Natural Gas Company [Member] | Real estate funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation, percentage	7.00%
Northwest Natural Gas Company [Member] | High yield bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation, percentage	5.00%
Northwest Natural Gas Company [Member] | Emerging market debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation, percentage	5.00%