Commitments and Contingencies - Schedule of Gas Purchase and Pipeline Capacity Purchase and Release Commitments (Details) - Northwest Natural Gas Company [Member] $ in Thousands	Dec. 31, 2018 USD ($)
Gas Purchase Agreements [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
2018	$ 144,500
2019	2,776
2020	2,313
2021	0
2022	0
Thereafter	0
Total	149,589
Less: Amount representing interest	1,314
Total at present value	148,275
Pipeline Capacity Purchase Agreements [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
2018	78,449
2019	76,613
2020	66,656
2021	61,075
2022	60,619
Thereafter	580,022
Total	923,434
Less: Amount representing interest	201,224
Total at present value	722,210
Pipeline Capacity Release Agreements [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
2018	4,272
2019	3,560
2020	0
2021	0
2022	0
Thereafter	0
Total	7,832
Less: Amount representing interest	183
Total at present value	$ 7,649