Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating revenues [Abstract]
Operating revenues	$ 706,143	$ 755,038	$ 668,173
Operating expenses:
Cost of gas	255,519	324,795	260,588
Operations and maintenance	156,698	152,358	136,723
Environmental remediation	11,127	15,291	13,298
General taxes	32,172	30,639	29,243
Revenue taxes	30,082	0	0
Depreciation and amortization	85,156	81,053	77,604
Other operating expenses	3,227	0	0
Total operating expenses	573,981	604,136	517,456
Income from operations	132,162	150,902	150,717
Other income (expense), net	(3,601)	(295)	(7,151)
Interest expense, net	37,059	37,526	38,136
Income before income taxes	91,502	113,081	105,430
Income tax expense	24,191	41,008	43,011
Net income from continuing operations	67,311	72,073	62,419
Loss from discontinued operations, net of tax	(2,742)	(127,696)	(3,524)
Net income (loss)	64,569	(55,623)	58,895
Other comprehensive income (loss):
Change in employee benefit plan liability, net of taxes of ($166) for 2018, $735 for 2017, and $452 for 2016	476	(2,059)	(744)
Amortization of non-qualified employee benefit plan liability, net of taxes of ($278) for 2018, ($374) for 2017, and ($624) for 2016	774	572	955
Comprehensive income (loss)	$ 65,819	$ (57,110)	$ 59,106
Average common shares outstanding:
Basic (in shares)	28,803	28,669	27,647
Diluted (in shares)	28,873	28,753	27,779
Earnings from continuing operations per share of common stock:
Basic (in dollars per share)	$ 2.34	$ 2.51	$ 2.26
Diluted (in dollars per share)	2.33	2.51	2.25
Loss from discontinued operations per share of common stock:
Basic (in dollars per share)	(0.10)	(4.45)	(0.13)
Diluted (in dollars per share)	(0.09)	(4.44)	(0.13)
Earnings (loss) per share of common stock:
Basic (in dollars per share)	2.24	(1.94)	2.13
Diluted (in dollars per share)	$ 2.24	$ (1.93)	$ 2.12
Northwest Natural Gas Company [Member]
Operating revenues [Abstract]
Operating revenues	$ 705,571	$ 755,038	$ 667,949
Operating expenses:
Cost of gas	255,743	325,019	260,588
Utility Operations and maintenance	155,225	152,180	135,979
Environmental remediation	11,127	15,291	13,298
General taxes	32,086	30,602	29,222
Revenue taxes	30,082	0	0
Depreciation and amortization	84,986	81,024	77,575
Other operating expenses	3,223	0	0
Total operating expenses	572,472	604,116	516,662
Income from operations	133,099	150,922	151,287
Other income (expense), net	(3,599)	(198)	(7,041)
Interest expense, net	36,992	37,526	38,136
Income before income taxes	92,508	113,198	106,110
Income tax expense	24,459	41,478	43,275
Net income from continuing operations	68,049	71,720	62,835
Loss from discontinued operations, net of tax	(1,723)	(127,343)	(3,940)
Net income (loss)	66,326	(55,623)	58,895
Other comprehensive income (loss):
Change in employee benefit plan liability, net of taxes of ($166) for 2018, $735 for 2017, and $452 for 2016	476	(2,059)	(744)
Amortization of non-qualified employee benefit plan liability, net of taxes of ($278) for 2018, ($374) for 2017, and ($624) for 2016	774	572	955
Comprehensive income (loss)	$ 67,576	$ (57,110)	$ 59,106