Pension and Other Postretirement Benefits Costs - Schedule of Fair Value of Plan Assets (Details) - Pension Plan [Member] - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	$ 257,797	$ 287,925
Northwest Natural Gas Company [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	257,797	287,925	$ 257,714
Total Pension Asset Investments Net Of Receivables And Payables	257,796	287,895
Accrued interest and dividend income	1	30
Due from broker for securities sold	0	0
Total receivables	1	30
Due to broker for securities purchased	0	0
Northwest Natural Gas Company [Member] | United States Equity [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	85,233	98,375
Northwest Natural Gas Company [Member] | Non-U.S. equity [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	95,011	106,029
Northwest Natural Gas Company [Member] | Liability hedging [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	45,659	53,981
Northwest Natural Gas Company [Member] | Opportunistic [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	23,186	23,895
Northwest Natural Gas Company [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	8,707	5,615
Northwest Natural Gas Company [Member] | Level 1 [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	24,994
Total Pension Asset Investments Net Of Receivables And Payables		21,293
Northwest Natural Gas Company [Member] | Level 1 [Member] | United States Equity [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	0	0
Northwest Natural Gas Company [Member] | Level 1 [Member] | Non-U.S. equity [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	24,994	21,211
Northwest Natural Gas Company [Member] | Level 1 [Member] | Liability hedging [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	0	0
Northwest Natural Gas Company [Member] | Level 1 [Member] | Opportunistic [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	0	0
Northwest Natural Gas Company [Member] | Level 1 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	0	82
Northwest Natural Gas Company [Member] | Level 2 [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	0
Total Pension Asset Investments Net Of Receivables And Payables		0
Northwest Natural Gas Company [Member] | Level 2 [Member] | United States Equity [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	0	0
Northwest Natural Gas Company [Member] | Level 2 [Member] | Non-U.S. equity [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	0	0
Northwest Natural Gas Company [Member] | Level 2 [Member] | Liability hedging [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	0	0
Northwest Natural Gas Company [Member] | Level 2 [Member] | Opportunistic [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	0	0
Northwest Natural Gas Company [Member] | Level 2 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	0	0
Northwest Natural Gas Company [Member] | Level 3 [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	0
Total Pension Asset Investments Net Of Receivables And Payables		0
Northwest Natural Gas Company [Member] | Level 3 [Member] | United States Equity [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	0	0
Northwest Natural Gas Company [Member] | Level 3 [Member] | Non-U.S. equity [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	0	0
Northwest Natural Gas Company [Member] | Level 3 [Member] | Liability hedging [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	0	0
Northwest Natural Gas Company [Member] | Level 3 [Member] | Opportunistic [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	0	0
Northwest Natural Gas Company [Member] | Level 3 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	0	0
Northwest Natural Gas Company [Member] | Fair Value Measured at NAV [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	232,802
Total Pension Asset Investments Net Of Receivables And Payables		266,602
Northwest Natural Gas Company [Member] | Fair Value Measured at NAV [Member] | United States Equity [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	85,233	98,375
Northwest Natural Gas Company [Member] | Fair Value Measured at NAV [Member] | Non-U.S. equity [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	70,017	84,818
Northwest Natural Gas Company [Member] | Fair Value Measured at NAV [Member] | Liability hedging [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	45,659	53,981
Northwest Natural Gas Company [Member] | Fair Value Measured at NAV [Member] | Opportunistic [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	23,186	23,895
Northwest Natural Gas Company [Member] | Fair Value Measured at NAV [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	$ 8,707	$ 5,533