Quarterly Financial Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Entity Information [Line Items]
Operating revenues	$ 226,702	$ 91,239	$ 124,567	$ 263,635	$ 238,626	$ 86,212	$ 134,476	$ 295,724	$ 706,143	$ 755,038	$ 668,173
Net income from continuing operations	36,783	(11,144)	(339)	42,011	34,488	(7,887)	4,075	41,397	67,311	72,073	62,419
Loss from discontinued operations, net of tax	(959)	(650)	(659)	(474)	(124,655)	(608)	(1,346)	(1,087)	(2,742)	(127,696)	(3,524)
Net income (loss)	$ 35,824	$ (11,794)	$ (998)	$ 41,537	$ (90,167)	$ (8,495)	$ 2,729	$ 40,310	$ 64,569	$ (55,623)	$ 58,895
Average common shares outstanding:
Average common shares outstanding - basic (in shares)	28,851	28,815	28,791	28,753	28,716	28,678	28,648	28,633	28,803	28,669	27,647
Diluted (in shares)	28,940	28,815	28,791	28,803	28,797	28,678	28,717	28,723	28,873	28,753	27,779
Earnings from continuing operations per share of common stock:
Basic (in dollars per share)	$ 1.27	$ (0.39)	$ (0.01)	$ 1.46	$ 1.20	$ (0.28)	$ 0.14	$ 1.45	$ 2.34	$ 2.51	$ 2.26
Diluted (in dollars per share)	1.27	(0.39)	(0.01)	1.46	1.20	(0.28)	0.14	1.44	2.33	2.51	2.25
Loss from discontinued operations per share of common stock:
Basic (in dollars per share)	(0.03)	(0.02)	(0.02)	(0.02)	(4.34)	(0.02)	(0.04)	(0.04)	(0.10)	(4.45)	(0.13)
Diluted (in dollars per share)	(0.03)	(0.02)	(0.02)	(0.02)	(4.33)	(0.02)	(0.04)	(0.04)	(0.09)	(4.44)	(0.13)
Earnings (loss) per share of common stock:
Basic (in dollars per share)	1.24	(0.41)	(0.03)	1.44	(3.14)	(0.30)	0.10	1.41	2.24	(1.94)	2.13
Diluted (in dollars per share)	$ 1.24	$ (0.41)	$ (0.03)	$ 1.44	$ (3.13)	$ (0.30)	$ 0.10	$ 1.40	$ 2.24	$ (1.93)	$ 2.12
Northwest Natural Gas Company [Member]
Entity Information [Line Items]
Operating revenues	$ 226,146	$ 91,227	$ 124,563	$ 263,635	$ 238,793	$ 86,157	$ 134,420	$ 295,668	$ 705,571	$ 755,038	$ 667,949
Net income from continuing operations	37,581	(11,275)	(271)	42,014	34,086	(7,876)	4,072	41,438	68,049	71,720	62,835
Loss from discontinued operations, net of tax	0	(519)	(727)	(477)	(124,253)	(619)	(1,343)	(1,128)	(1,723)	(127,343)	(3,940)
Net income (loss)	$ 37,581	$ (11,794)	$ (998)	$ 41,537	$ (90,167)	$ (8,495)	$ 2,729	$ 40,310	$ 66,326	$ (55,623)	$ 58,895