Income Tax (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2018
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income taxes at statutory rates (federal and state)	$ (1,429)	$ 480	$ 11,676	$ 11,502
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount	(333)	214	3,344	3,505
Differences required to be flowed-through by regulatory commissions	173	(37)	(2,352)	(5,297)
Other, net	(83)	(32)	(213)	(410)
Total provision for income taxes on continuing operations	$ (1,672)	$ 625	$ 12,455	$ 9,300
Effective tax rate for continuing operations	24.60%	23.40%	22.40%	17.00%
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)	$ (1,287)	$ 765	$ 12,068	$ 11,924
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount	(281)	290	3,456	3,616
Differences required to be flowed-through by regulatory commissions	173	(37)	(2,352)	(5,297)
Other, net	(24)	(33)	(173)	(410)
Total provision for income taxes on continuing operations	$ (1,419)	$ 985	$ 12,999	$ 9,833
Effective tax rate for continuing operations	23.10%	24.40%	22.60%	17.30%