Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	$ 281,005	$ 302,493
Revenues	285,151	285,348
Operating leases	28	48
Natural Gas Sales [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	274,004	296,186
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	2,336	2,783
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	150	1,506
Appliance Center Revenue [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	1,556	1,516
Other revenue [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	2,959	502
Alternative revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues	(472)	(17,253)
Leasing revenue [Member]
Disaggregation of Revenue [Line Items]
Operating leases	4,618	108
Northwest Natural Gas Company [Member]
Disaggregation of Revenue [Line Items]
Revenues	282,529	284,846
Northwest Natural Gas Company [Member] | Northwest Natural Gas Company [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	278,383	301,991
Revenues	282,529	284,846
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	274,004	296,186
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	2,336	2,783
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	150	1,506
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	1,556	1,516
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	337	0
Northwest Natural Gas Company [Member] | Northwest Natural Gas Company [Member] | Alternative revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues	(472)	(17,253)
Northwest Natural Gas Company [Member] | Northwest Natural Gas Company [Member] | Leasing revenue [Member]
Disaggregation of Revenue [Line Items]
Operating leases	4,618	108
Operating Segments [Member] | Natural Gas Distribution [Member]
Disaggregation of Revenue [Line Items]
Revenues	278,487	279,041
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	274,341	296,186
Revenues	278,487	279,041
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	274,004	296,186
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
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
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
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	337	0
Operating Segments [Member] | Natural Gas Distribution [Member] | Northwest Natural Gas Company [Member] | Alternative revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues	(472)	(17,253)
Operating Segments [Member] | Natural Gas Distribution [Member] | Northwest Natural Gas Company [Member] | Leasing revenue [Member]
Disaggregation of Revenue [Line Items]
Operating leases	4,618	108
Operating Segments [Member] | Northwest Natural Gas Company [Member]
Disaggregation of Revenue [Line Items]
Revenues	282,529	284,846
Corporate, Non-Segment [Member] | Other Northwest Natural [Member]
Disaggregation of Revenue [Line Items]
Revenues	4,042	5,805
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	4,042	5,805
Revenues	4,042	5,805
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
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	2,336	2,783
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	150	1,506
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	1,556	1,516
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
Corporate, Non-Segment [Member] | Other Northwest Natural [Member] | Northwest Natural Gas Company [Member] | Alternative revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues	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
Corporate, Non-Segment [Member] | Other Northwest Holdings [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	2,622	502
Revenues	2,622	502
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
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
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
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
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	2,622	502
Corporate, Non-Segment [Member] | Other Northwest Holdings [Member] | Alternative revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues	0	0
Corporate, Non-Segment [Member] | Other Northwest Holdings [Member] | Leasing revenue [Member]
Disaggregation of Revenue [Line Items]
Operating leases	$ 0	$ 0