Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating revenues [Abstract]
Operating revenues	$ 315,946	$ 285,151
Operating expenses:
Cost of gas	112,210	108,538
Operations and maintenance	52,191	48,921
Environmental remediation	3,777	4,005
General taxes	11,369	9,895
Revenue taxes	12,664	11,743
Depreciation and amortization	28,097	24,675
Other operating expenses	932	928
Total operating expenses	221,240	208,705
Income from operations	94,706	76,446
Other income (expense), net	(3,542)	(3,575)
Interest expense, net	11,126	10,468
Income before income taxes	80,038	62,403
Income tax expense	20,521	14,127
Net income from continuing operations	59,517	48,276
Loss from discontinued operations, net of tax	0	(778)
Net income	59,517	47,498
Other comprehensive income:
Amortization of non-qualified employee benefit plan liability, net of taxes	221	160
Comprehensive income	$ 59,738	$ 47,658
Average common shares outstanding:
Basic (in shares)	30,614	30,491
Diluted (in shares)	30,633	30,535
Earnings from continuing operations per share of common stock:
Basic (in dollars per share)	$ 1.94	$ 1.58
Diluted (in dollars per share)	1.94	1.58
Loss from discontinued operations per share of common stock:
Basic (in dollars per share)	0	(0.02)
Diluted (in dollars per share)	0	(0.02)
Earnings (loss) per share of common stock:
Basic (in dollars per share)	1.94	1.56
Diluted (in dollars per share)	$ 1.94	$ 1.56
Northwest Natural Gas Company [Member]
Operating revenues [Abstract]
Operating revenues	$ 312,350	$ 282,529
Operating expenses:
Cost of gas	112,266	108,595
Operations and maintenance	49,187	46,256
Environmental remediation	3,777	4,005
General taxes	11,259	9,799
Revenue taxes	12,655	11,743
Depreciation and amortization	27,169	24,190
Other operating expenses	919	920
Total operating expenses	217,232	205,508
Income from operations	95,118	77,021
Other income (expense), net	(3,665)	(3,563)
Interest expense, net	10,790	9,861
Income before income taxes	80,663	63,597
Income tax expense	20,552	14,418
Net income	60,111	49,179
Other comprehensive income:
Amortization of non-qualified employee benefit plan liability, net of taxes	221	160
Comprehensive income	60,332	49,339
Supplemental Income Statement Elements [Abstract]
Amortization of non-qualified employee benefit plan liability, tax	$ 80	$ 58