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	43,201		43,201		43,895		43,895
Dividends on common stock			(14,015)				(12,935)
Stranded Deferred Tax Remeasurement Benefit	1,366
Stranded Deferred Tax Remeasurement Benefit | Accounting Standards Update 2018-02 [Member]			1,366	(1,366)			1,366	(1,366)
Other comprehensive income	43,316			115	44,010			115
Stock-based compensation		1,245
Shares issued pursuant to equity based plans		1,047
Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs		0
Ending Balance at Mar. 31, 2019	$ 794,227	459,932	342,734	(8,439)	746,743	$ 226,452	528,730	(8,439)
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	47,498		47,498		49,179		49,179
Dividends on common stock			(14,898)				(13,796)
Stranded Deferred Tax Remeasurement Benefit	0
Stranded Deferred Tax Remeasurement Benefit | Accounting Standards Update 2018-02 [Member]			0	0			0	0
Other comprehensive income	47,658			160	49,339			160
Stock-based compensation		3,378
Shares issued pursuant to equity based plans		(390)
Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs		(6)
Ending Balance at Mar. 31, 2020	$ 901,741	$ 561,264	$ 351,050	$ (10,573)	$ 857,739	$ 319,557	$ 548,755	$ (10,573)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per share of common stock	$ 0.4775