Income Tax (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income taxes at statutory rates (federal and state)	$ (6,507)	$ (4,136)	$ 8,500	$ 11,097
Differences required to be flowed-through by regulatory commissions	2,090	(266)	(3,207)	569
Other, net	74	117	(336)	(475)
Total provision for income taxes on continuing operations	$ (4,343)	$ (4,285)	$ 4,957	$ 11,191
Effective tax rate for continuing operations	19.00%	27.80%	15.50%	26.80%
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%		35.00%
Northwest Natural Gas Company [Member]
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income taxes at statutory rates (federal and state)	$ (6,177)	$ (4,183)	$ 9,363	$ 11,081
Differences required to be flowed-through by regulatory commissions	2,090	(266)	(3,207)	569
Other, net	74	116	(336)	(476)
Total provision for income taxes on continuing operations	$ (4,013)	$ (4,333)	$ 5,820	$ 11,174
Effective tax rate for continuing operations	18.60%	27.80%	16.50%	26.80%