Environmental Matters (Details) - USD ($)	1 Months Ended	3 Months Ended	12 Months Ended
	Jan. 31, 2016	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Environmental Regulatory Table [Abstract]
Regulatory Assets, Current			$ 41,930,000	$ 45,781,000
Regulatory Assets, Noncurrent			$ 371,786,000	356,608,000
Northwest Natural Gas Company [Member]
Environmental Activity [Line Items]
Remediation Recovery Percentage			96.68%
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Current Liabilities			$ 33,112,000	19,088,000
Environmental Noncurrent Liabilities			95,636,000	108,280,000
EPA Record Of Decision, Clean-Up Costs, Portland Harbor			$ 1,050,000,000
Number Of Potentially Responsible Parties			more than 100
Loss Contingency Range Of Possible Loss Gasco Siltronic			$49.5 million to $350 million
Environmental Project Liability			$ 49,500,000
NRD Liability Claim Yakama Nation			300,000
Undiscounted Environmental Remediation Expense		$ 10,500,000
Liability For Studies And Design Costs			900,000
Pre-tax Regulatory Disallowance			15,000,000
Deferred Environmental Charges			95,000,000
Disallowance From Order, Interest Portion	$ 2,800,000
Environmental Costs to be Amortized	13,800,000
Total Disallowance From Order	3,300,000
Disallowance From Order, Operations and Maintenance Portion	$ 500,000
Annual Tariff Rider Collection			5,000,000
Environmental Settlement Insurance Proceeds Received To Date			150,000,000
Annual insurance proceeds to appy against remediation costs			5,000,000
Insurance Proceeds Applied To Prudently Incurred Remediation Costs			73,200,000
Environmental Regulatory Table [Abstract]
Regulatory Assets, Current			41,930,000	45,781,000
Regulatory Assets, Noncurrent			$ 371,786,000	356,608,000
Remediation Non-recovery Percentage			3.32%
Annual Insurance Proceeds to Apply Against Remediation Costs			$ 5,000,000
Total Annual Remediation Expense and Interest			10,000,000
Northwest Natural Gas Company [Member] | Minimum [Member]
Accrual for Environmental Loss Contingencies [Abstract]
EPA Record Of Decision, Clean-Up Costs, Portland Harbor			(0.30)
Northwest Natural Gas Company [Member] | Maximum [Member]
Accrual for Environmental Loss Contingencies [Abstract]
EPA Record Of Decision, Clean-Up Costs, Portland Harbor			0.50
Northwest Natural Gas Company [Member] | Gasco Siltronic Sediments [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Current Liabilities			5,117,000	2,683,000
Environmental Noncurrent Liabilities			44,351,000	45,346,000
Northwest Natural Gas Company [Member] | Portland Harbor Other [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Current Liabilities			2,600,000	1,949,000
Environmental Noncurrent Liabilities			6,273,000	4,163,000
Northwest Natural Gas Company [Member] | Gasco Upland [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Current Liabilities			13,983,000	13,422,000
Environmental Noncurrent Liabilities			44,830,000	47,835,000
Northwest Natural Gas Company [Member] | Central Service Center [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Current Liabilities			10,000	25,000
Environmental Noncurrent Liabilities			0	0
Northwest Natural Gas Company [Member] | Front Street [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Current Liabilities			11,402,000	1,009,000
Environmental Noncurrent Liabilities			3,000	10,757,000
Northwest Natural Gas Company [Member] | Oregon Steel Mills [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Current Liabilities			0	0
Environmental Noncurrent Liabilities			179,000	179,000
Northwest Natural Gas Company [Member] | Environmental Restoration Costs [Member]
Environmental Regulatory Table [Abstract]
Environmental Regulatory Deferred Cost and Interest			41,883,000	45,546,000
Environmental Regulatory Accrued Site Liabilities			128,369,000	126,950,000
Environmental Regulatory Insurance Proceeds and Interest			(88,502,000)	(94,170,000)
Environmental Regulatory Assets Noncurrent			81,750,000	78,326,000
Regulatory Assets, Current			5,601,000	6,198,000
Regulatory Assets, Noncurrent			76,149,000	72,128,000
Northwest Natural Gas Company [Member] | Environmental Restoration Costs [Member] | Front Street [Member]
Environmental Regulatory Table [Abstract]
Environmental Regulatory Accrued Site Liabilities			$ 400,000	$ 400,000
Northwest Natural Gas Company [Member] | Oregon [Member]
Environmental Activity [Line Items]
Remediation Recovery Percentage			96.68%