Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating revenues [Abstract]
Operating revenues	$ 285,151	$ 285,348
Operating expenses:
Cost of gas	108,538	105,457
Operations and maintenance	48,921	51,482
Environmental remediation	4,005	8,947
General taxes	9,895	9,027
Excise Taxes	11,743	11,926
Depreciation and amortization	24,675	21,572
Other operating expenses	928	892
Total operating expenses	208,705	209,303
Income from operations	76,446	76,045
Other income (expense), net	(3,575)	(13,747)
Interest expense, net	10,468	10,205
Income before income taxes	62,403	52,093
Income tax expense	14,127	8,675
Net income from continuing operations	48,276	43,418
Loss from discontinued operations, net of tax	(778)	(217)
Net income	47,498	43,201
Other comprehensive income:
Amortization of non-qualified employee benefit plan liability, net of taxes	160	115
Comprehensive income	$ 47,658	$ 43,316
Average common shares outstanding:
Basic (in shares)	30,491	28,906
Diluted (in shares)	30,535	28,970
Earnings from continuing operations per share of common stock:
Basic (in dollars per share)	$ 1.58	$ 1.50
Diluted (in dollars per share)	1.58	1.50
Loss from discontinued operations per share of common stock:
Basic (in dollars per share)	(0.02)	(0.01)
Diluted (in dollars per share)	(0.02)	(0.01)
Earnings (loss) per share of common stock:
Basic (in dollars per share)	1.56	1.49
Diluted (in dollars per share)	$ 1.56	$ 1.49
Northwest Natural Gas Company [Member]
Operating revenues [Abstract]
Operating revenues	$ 282,529	$ 284,846
Operating expenses:
Cost of gas	108,595	105,513
Operations and maintenance	46,256	50,434
Environmental remediation	4,005	8,947
General taxes	9,799	8,988
Excise Taxes	11,743	11,926
Depreciation and amortization	24,190	21,504
Other operating expenses	920	890
Total operating expenses	205,508	208,202
Income from operations	77,021	76,644
Other income (expense), net	(3,563)	(13,768)
Interest expense, net	9,861	10,133
Income before income taxes	63,597	52,743
Income tax expense	14,418	8,848
Net income	49,179	43,895
Other comprehensive income:
Amortization of non-qualified employee benefit plan liability, net of taxes	160	115
Comprehensive income	$ 49,339	$ 44,010