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] 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, 2018	$ 762,634	$ 457,640	$ 312,182	$ (7,188)	$ 715,668	$ 226,452	$ 496,404	$ (7,188)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustments to Additional Paid in Capital, Other						93,182
Net income	24,995		24,995		29,361		29,361
Dividends on common stock			(42,287)				(39,601)
Reclassification of tax effects from the TCJA	1,366
Reclassification of tax effects from the TCJA | Accounting Standards Update 2018-02 [Member]			1,366	(1,366)			1,366	(1,366)
Other comprehensive income	25,339			344	29,705			344
Stock-based compensation		2,309
Shares issued pursuant to equity based plans		3,718
Stock issuance and costs		92,956
Ending Balance at Sep. 30, 2019	$ 844,669	556,623	296,256	(8,210)	798,954	319,634	487,530	(8,210)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per share of common stock	$ 1.4250
Beginning Balance at Jun. 30, 2019	$ 876,746	555,052	330,018	(8,324)	830,115	319,634	518,805	(8,324)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustments to Additional Paid in Capital, Other						0
Net income	(19,301)		(19,301)		(17,588)		(17,588)
Dividends on common stock			(14,461)				(13,687)
Reclassification of tax effects from the TCJA	0
Reclassification of tax effects from the TCJA | Accounting Standards Update 2018-02 [Member]			0	0			0	0
Other comprehensive income	(19,187)			114	(17,474)			114
Stock-based compensation		485
Shares issued pursuant to equity based plans		1,082
Stock issuance and costs		4
Ending Balance at Sep. 30, 2019	$ 844,669	556,623	296,256	(8,210)	798,954	319,634	487,530	(8,210)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per share of common stock	$ 0.4750
Beginning 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]
Adjustments to Additional Paid in Capital, Other						0
Net income	24,734		24,734		24,247		24,247
Dividends on common stock			(44,034)				(41,444)
Reclassification of tax effects from the TCJA	0
Reclassification of tax effects from the TCJA | Accounting Standards Update 2018-02 [Member]			0	0			0	0
Other comprehensive income	25,240			506	24,753			506
Stock-based compensation		4,091
Shares issued pursuant to equity based plans		1,485
Stock issuance and costs		(6)
Ending Balance at Sep. 30, 2020	$ 852,775	563,852	299,150	(10,227)	805,505	319,557	496,175	(10,227)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per share of common stock	$ 1.4325
Beginning Balance at Jun. 30, 2020	$ 884,001	562,766	331,648	(10,413)	839,369	319,557	530,225	(10,413)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustments to Additional Paid in Capital, Other						0
Net income	(17,912)		(17,912)		(20,220)		(20,220)
Dividends on common stock			(14,586)				(13,830)
Reclassification of tax effects from the TCJA	0
Reclassification of tax effects from the TCJA | Accounting Standards Update 2018-02 [Member]			0	0			0	0
Other comprehensive income	(17,726)			186	(20,034)			186
Stock-based compensation		459
Shares issued pursuant to equity based plans		627
Stock issuance and costs		0
Ending Balance at Sep. 30, 2020	$ 852,775	$ 563,852	$ 299,150	$ (10,227)	$ 805,505	$ 319,557	$ 496,175	$ (10,227)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per share of common stock	$ 0.4775