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		$ 496,404	$ (7,188)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	44,296		44,296		46,949		46,949
Dividends on common stock			(27,826)				(25,914)
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	44,526			230	47,179			230
Stock-based compensation		1,824
Shares issued pursuant to equity based plans		2,636
Stock issuance and costs		92,952
Ending 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]
Dividends per share of common stock	$ 0.9500
Beginning Balance at Mar. 31, 2019	$ 794,227	459,932	342,734	(8,439)	746,743		528,730	(8,439)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,095		1,095		3,054		3,054
Dividends on common stock			(13,811)				(12,979)
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	1,210			115	3,169			115
Stock-based compensation		579
Shares issued pursuant to equity based plans		1,589
Stock issuance and costs		92,952
Ending 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]
Dividends per share of common stock	$ 0.4750
Beginning Balance at Dec. 31, 2019	$ 865,999	558,282	318,450	(10,733)	822,196		513,372	(10,733)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	42,646		42,646		44,467		44,467
Dividends on common stock			(29,448)				(27,614)
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	42,966			320	44,787			320
Stock-based compensation		3,632
Shares issued pursuant to equity based plans		858
Stock issuance and costs		(6)
Ending 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]
Dividends per share of common stock	$ 0.9550
Beginning Balance at Mar. 31, 2020	$ 901,741	561,264	351,050	(10,573)	857,739		548,755	(10,573)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	(4,852)		(4,852)		(4,712)		(4,712)
Dividends on common stock			(14,550)				(13,818)
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	(4,692)			160	(4,552)			160
Stock-based compensation		254
Shares issued pursuant to equity based plans		1,248
Stock issuance and costs		0
Ending 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]
Dividends per share of common stock	$ 0.4775