Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	$ 87,981	$ 88,520	$ 508,052	$ 473,228
Revenues	90,317	91,239	499,108	479,441
Operating leases	48		143
Natural Gas Sales [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	80,480	82,358	488,681	455,312
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	2,333	2,415	7,856	7,189
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	1,208	2,714	3,174	6,974
Appliance Center Revenue [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	988	1,021	3,562	3,737
Other revenue [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	2,972	12	4,779	16
Alternative revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues	(2,607)	1,994	(16,126)	5,285
Leasing revenue [Member]
Disaggregation of Revenue [Line Items]
Operating leases	4,943	725	7,182	928
Northwest Natural Gas Company [Member]
Disaggregation of Revenue [Line Items]
Revenues	87,592	91,227	494,680	479,425
Northwest Natural Gas Company [Member] | Northwest Natural Gas Company [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	85,256	88,508	503,624	473,212
Revenues	87,592	91,227	494,680	479,425
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	80,480	82,358	488,681	455,312
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	2,333	2,415	7,856	7,189
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	1,208	2,714	3,174	6,974
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	988	1,021	3,562	3,737
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	247	0	351	0
Northwest Natural Gas Company [Member] | Northwest Natural Gas Company [Member] | Alternative revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues	(2,607)	1,994	(16,126)	5,285
Northwest Natural Gas Company [Member] | Northwest Natural Gas Company [Member] | Leasing revenue [Member]
Disaggregation of Revenue [Line Items]
Operating leases	4,943	725	7,182	928
Operating Segments [Member] | Natural Gas Distribution [Member]
Disaggregation of Revenue [Line Items]
Revenues	83,063	85,077	480,088	461,525
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	80,727	82,358	489,032	455,312
Revenues	83,063	85,077	480,088	461,525
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	80,480	82,358	488,681	455,312
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	247	0	351	0
Operating Segments [Member] | Natural Gas Distribution [Member] | Northwest Natural Gas Company [Member] | Alternative revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues	(2,607)	1,994	(16,126)	5,285
Operating Segments [Member] | Natural Gas Distribution [Member] | Northwest Natural Gas Company [Member] | Leasing revenue [Member]
Disaggregation of Revenue [Line Items]
Operating leases	4,943	725	7,182	928
Operating Segments [Member] | Northwest Natural Gas Company [Member]
Disaggregation of Revenue [Line Items]
Revenues	87,592	91,227	494,680	479,425
Corporate, Non-Segment [Member] | Other Northwest Natural [Member]
Disaggregation of Revenue [Line Items]
Revenues	4,529	6,150	14,592	17,900
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	4,529	6,150	14,592	17,900
Revenues	4,529	6,150	14,592	17,900
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	2,333	2,415	7,856	7,189
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	1,208	2,714	3,174	6,974
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	988	1,021	3,562	3,737
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	2,725	12	4,428	16
Revenues	2,725	12	4,428	16
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	2,725	12	4,428	16
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