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, 2017	$ 742,776	$ 448,865	$ 302,349	$ (8,438)	$ 742,776	$ 448,865	$ 302,349	$ (8,438)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	41,537		41,537		41,537		41,537
Other comprehensive income	41,691			154	41,691			154
Dividends on common stock			(13,805)				(13,805)
Stranded Deferred Tax Remeasurement Benefit	0
Stranded Deferred Tax Remeasurement Benefit | Accounting Standards Update 2018-02 [Member]			0	0			0	0
Stock-based compensation		1,172				1,172
Shares issued pursuant to equity based plans		371				371
Ending Balance at Mar. 31, 2018	$ 772,205	450,408	330,081	(8,284)	772,205	450,408	330,081	(8,284)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends per share of common stock	$ 0.4725
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]
Net income	43,201		43,201		43,895		43,895
Other comprehensive income	43,316			115	44,010			115
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]	1,400		1,400	(1,400)			1,400	(1,400)
Stock-based compensation		1,245				0
Shares issued pursuant to equity based plans		1,047				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