Consolidated Statement of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock Including APIC [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Northwest Natural Gas Company [Member]	Northwest Natural Gas Company [Member] Northwest Natural Gas Company Consolidated [Member]	Northwest Natural Gas Company [Member] Common Stock Including APIC [Member]	Northwest Natural Gas Company [Member] Retained Earnings [Member]	Northwest Natural Gas Company [Member] Accumulated Other Comprehensive Income (Loss) [Member]
Beginning Balance at Dec. 31, 2017	$ 742,776	$ 448,865	$ 302,349	$ (8,438)		$ 742,776	$ 448,865	$ 302,349	$ (8,438)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	65,819	0	64,569	1,250	$ 67,576	67,576	0	66,326	1,250
Dividends on common stock	(54,736)	0	(54,736)	0		(41,035)	0	(41,035)	0
Stock-based compensation	3,020	3,020	0	0		2,161	2,161	0	0
Shares issued pursuant to equity based plans	5,175	5,175	0	0		3,075	3,075	0	0
Transfer from Investments						58,885	227,649	(168,764)	0
Capital contributions					0
Cash purchase of shares for business combination	(7,945)	(7,945)	0	0
Value of shares transferred for business combination	8,525	8,525	0	0
Ending Balance at Dec. 31, 2018	$ 762,634	457,640	312,182	(7,188)		715,668	226,452	496,404	(7,188)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends on common stock (in dollars per share)	$ 1.89
Comprehensive income	$ 59,556	0	61,735	(2,179)	66,795	66,795	0	68,974	(2,179)
Dividends on common stock	(56,833)	0	(56,833)	0		(53,372)	0	(53,372)	0
Stock-based compensation	2,601	2,601	0	0
Shares issued pursuant to equity based plans	5,085	5,085	0	0
Capital contributions					93,155	93,105	93,105	0	0
Issuance of common stock, net of issuance costs	92,956	92,956	0	0
Reclassification of tax effects from the TCJA	0	0	1,366	(1,366)		0	0	1,366	(1,366)
Ending Balance at Dec. 31, 2019	$ 865,999	558,282	318,450	(10,733)		822,196	319,557	513,372	(10,733)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends on common stock (in dollars per share)	$ 1.90
Comprehensive income	$ 74,612	0	76,781	(2,169)	68,394	68,394	0	70,563	(2,169)
Dividends on common stock	(58,708)	0	(58,708)	0		(55,355)	0	(55,355)	0
Stock-based compensation	4,361	4,361	0	0
Shares issued pursuant to equity based plans	2,469	2,469	0	0
Capital contributions					$ 0
Stockholders' Equity, Other						(51)	(51)	0	0
Ending Balance at Dec. 31, 2020	$ 888,733	$ 565,112	$ 336,523	$ (12,902)		$ 835,184	$ 319,506	$ 528,580	$ (12,902)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends on common stock (in dollars per share)	$ 1.91