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, 2015	$ 780,972	$ 383,144	$ 404,990	$ (7,162)	$ 780,972		$ 383,144		$ 404,990		$ (7,162)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	59,106	0	58,895	211	59,106		0		58,895		211
Dividends on common stock	(51,624)	0	(51,624)	0	(51,624)		0		(51,624)		0
Stock-based compensation	2,924	2,924	0	0	2,924		2,924		0		0
Shares issued pursuant to equity based plans	6,358	6,358	0	0	6,358		6,358		0		0
Issuance of common stock, net of issuance costs	52,761	52,761	0	0	52,761		52,761		0		0
Ending Balance at Dec. 31, 2016	$ 850,497	445,187	412,261	(6,951)	850,497		445,187		412,261		(6,951)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends on common stock (in dollars per share)	$ 1.87
Comprehensive income	$ (57,110)	0	(55,623)	(1,487)	(57,110)		0		(55,623)		(1,487)
Dividends on common stock	(54,289)	0	(54,289)	0	(54,289)		0		(54,289)		0
Stock-based compensation	2,882	2,882	0	0	2,882		2,882		0		0
Shares issued pursuant to equity based plans	796	796	0	0	796		796		0		0
Ending 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]
Dividends on common stock (in dollars per share)	$ 1.88
Comprehensive income	$ 65,819	0	64,569	1,250	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	[1]	2,161	[1]	0	[1]	0	[1]
Shares issued pursuant to equity based plans	5,175	5,175	0	0	3,075	[1]	3,075	[1]	0	[1]	0	[1]
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
Transfer of investments to NW Holdings					(58,885)		(227,649)		168,764		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

[1] Stock-based compensation is based on stock awards of NW Natural to be issued in shares of NW Holdings.