Revenue - Disaggregation of Revenue - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	$ 88,283	$ 87,981	$ 494,281	$ 508,052
Revenues	93,284	90,317	513,406	499,108
Operating leases	18	48	71	143
Natural Gas Sales [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	78,427	80,480	469,113	488,681
Gas Storage Revenue, Net of Regulatory Sharing [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	2,482	2,333	7,267	7,856
Asset Management Revenue, Net of Regulatory Sharing [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	939	1,208	1,999	3,174
Appliance Center Revenue [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	1,185	988	3,547	3,562
Other revenue [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	5,250	2,972	12,355	4,779
Alternative revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues	395	(2,607)	5,288	(16,126)
Leasing revenue [Member]
Disaggregation of Revenue [Line Items]
Operating leases	4,606	4,943	13,837	7,182
Northwest Natural Gas Company [Member]
Disaggregation of Revenue [Line Items]
Revenues	88,367	87,592	502,053	494,680
Northwest Natural Gas Company [Member] | Northwest Natural Gas Company [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	83,366	85,256	482,928	503,624
Revenues	88,367	87,592	502,053	494,680
Northwest Natural Gas Company [Member] | Northwest Natural Gas Company [Member] | Natural Gas Sales [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	78,427	80,480	469,113	488,681
Northwest Natural Gas Company [Member] | Northwest Natural Gas Company [Member] | Gas Storage Revenue, Net of Regulatory Sharing [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	2,482	2,333	7,267	7,856
Northwest Natural Gas Company [Member] | Northwest Natural Gas Company [Member] | Asset Management Revenue, Net of Regulatory Sharing [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	939	1,208	1,999	3,174
Northwest Natural Gas Company [Member] | Northwest Natural Gas Company [Member] | Appliance Center Revenue [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	1,185	988	3,547	3,562
Northwest Natural Gas Company [Member] | Northwest Natural Gas Company [Member] | Other revenue [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	333	247	1,002	351
Northwest Natural Gas Company [Member] | Northwest Natural Gas Company [Member] | Alternative revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues	395	(2,607)	5,288	(16,126)
Northwest Natural Gas Company [Member] | Northwest Natural Gas Company [Member] | Leasing revenue [Member]
Disaggregation of Revenue [Line Items]
Operating leases	4,606	4,943	13,837	7,182
Operating Segments [Member] | Natural Gas Distribution [Member]
Disaggregation of Revenue [Line Items]
Revenues	83,761	83,063	489,240	480,088
Operating Segments [Member] | Natural Gas Distribution [Member] | Northwest Natural Gas Company [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	78,760	80,727	470,115	489,032
Revenues	83,761	83,063	489,240	480,088
Operating Segments [Member] | Natural Gas Distribution [Member] | Northwest Natural Gas Company [Member] | Natural Gas Sales [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	78,427	80,480	469,113	488,681
Operating Segments [Member] | Natural Gas Distribution [Member] | Northwest Natural Gas Company [Member] | Gas Storage Revenue, Net of Regulatory Sharing [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	0	0	0	0
Operating Segments [Member] | Natural Gas Distribution [Member] | Northwest Natural Gas Company [Member] | Asset Management Revenue, Net of Regulatory Sharing [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	0	0	0	0
Operating Segments [Member] | Natural Gas Distribution [Member] | Northwest Natural Gas Company [Member] | Appliance Center Revenue [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	0	0	0	0
Operating Segments [Member] | Natural Gas Distribution [Member] | Northwest Natural Gas Company [Member] | Other revenue [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	333	247	1,002	351
Operating Segments [Member] | Natural Gas Distribution [Member] | Northwest Natural Gas Company [Member] | Alternative revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues	395	(2,607)	5,288	(16,126)
Operating Segments [Member] | Natural Gas Distribution [Member] | Northwest Natural Gas Company [Member] | Leasing revenue [Member]
Disaggregation of Revenue [Line Items]
Operating leases	4,606	4,943	13,837	7,182
Operating Segments [Member] | Northwest Natural Gas Company [Member]
Disaggregation of Revenue [Line Items]
Revenues	88,367	87,592	502,053	494,680
Corporate, Non-Segment [Member] | Other Northwest Natural [Member]
Disaggregation of Revenue [Line Items]
Revenues	4,606	4,529	12,813	14,592
Corporate, Non-Segment [Member] | Other Northwest Natural [Member] | Northwest Natural Gas Company [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	4,606	4,529	12,813	14,592
Revenues	4,606	4,529	12,813	14,592
Corporate, Non-Segment [Member] | Other Northwest Natural [Member] | Northwest Natural Gas Company [Member] | Natural Gas Sales [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Corporate, Non-Segment [Member] | Other Northwest Natural [Member] | Northwest Natural Gas Company [Member] | Gas Storage Revenue, Net of Regulatory Sharing [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	2,482	2,333	7,267	7,856
Corporate, Non-Segment [Member] | Other Northwest Natural [Member] | Northwest Natural Gas Company [Member] | Asset Management Revenue, Net of Regulatory Sharing [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	939	1,208	1,999	3,174
Corporate, Non-Segment [Member] | Other Northwest Natural [Member] | Northwest Natural Gas Company [Member] | Appliance Center Revenue [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1,185	988	3,547	3,562
Corporate, Non-Segment [Member] | Other Northwest Natural [Member] | Northwest Natural Gas Company [Member] | Other revenue [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Corporate, Non-Segment [Member] | Other Northwest Natural [Member] | Northwest Natural Gas Company [Member] | Alternative revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Corporate, Non-Segment [Member] | Other Northwest Natural [Member] | Northwest Natural Gas Company [Member] | Leasing revenue [Member]
Disaggregation of Revenue [Line Items]
Operating leases	0	0	0	0
Corporate, Non-Segment [Member] | Other Northwest Holdings [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	4,917	2,725	11,353	4,428
Revenues	4,917	2,725	11,353	4,428
Corporate, Non-Segment [Member] | Other Northwest Holdings [Member] | Natural Gas Sales [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Corporate, Non-Segment [Member] | Other Northwest Holdings [Member] | Gas Storage Revenue, Net of Regulatory Sharing [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Corporate, Non-Segment [Member] | Other Northwest Holdings [Member] | Asset Management Revenue, Net of Regulatory Sharing [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Corporate, Non-Segment [Member] | Other Northwest Holdings [Member] | Appliance Center Revenue [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0	0	0	0
Corporate, Non-Segment [Member] | Other Northwest Holdings [Member] | Other revenue [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	4,917	2,725	11,353	4,428
Corporate, Non-Segment [Member] | Other Northwest Holdings [Member] | Alternative revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Corporate, Non-Segment [Member] | Other Northwest Holdings [Member] | Leasing revenue [Member]
Disaggregation of Revenue [Line Items]
Operating leases	$ 0	$ 0	$ 0	$ 0