Pension and Other Postretirement Benefits Costs - Changes in Benefit Obligations and Fair Value of Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension Plan [Member]
Reconciliation of change in plan assets:
Fair value of plan assets at January 1	$ 373,931
Fair value of plan assets at December 31	399,217	$ 373,931
Qualified Pension Plans, Defined Benefit [Member]
Reconciliation of change in plan assets:
Defined Benefit Plan, Accumulated Benefit Obligation	464,400	480,000
Northwest Natural Gas Company [Member] | Other Postretirement Benefits Plan [Member]
Reconciliation of change in benefit obligation:
Obligation at January 1	29,039	29,568
Service cost	238	258
Interest cost	684	905
Net actuarial (gain) loss	(688)	145
Benefits paid	(2,050)	(1,837)	$ (1,774)
Obligation at December 31	27,223	29,039	29,568
Reconciliation of change in plan assets:
Fair value of plan assets at January 1	0	0
Actual return on plan assets	0	0
Employer contributions	2,050	1,837
Benefits paid	(2,050)	(1,837)	(1,774)
Fair value of plan assets at December 31	0	0	0
Northwest Natural Gas Company [Member] | Pension Plan [Member]
Reconciliation of change in benefit obligation:
Obligation at January 1	566,147	515,668
Service cost	6,982	6,614
Interest cost	13,447	16,161
Net actuarial (gain) loss	(18,587)	52,777
Benefits paid	(25,371)	(25,073)	(23,160)
Obligation at December 31	542,618	566,147	515,668
Reconciliation of change in plan assets:
Fair value of plan assets at January 1	373,932	313,051
Actual return on plan assets	38,712	54,600
Employer contributions	11,944	31,354
Benefits paid	(25,371)	(25,073)	(23,160)
Fair value of plan assets at December 31	399,217	373,932	$ 313,051
Defined Benefit Plan, Benefit Obligation, Period Increase (Decrease)	(21,300)
Defined Benefit Plan, Plan Assets, Period Increase (Decrease)	25,300
Northwest Natural Gas Company [Member] | Non-qualified Benefit Plans
Reconciliation of change in plan assets:
Defined Benefit Plan, Benefit Obligation, Period Increase (Decrease)	2,300
Northwest Natural Gas Company [Member] | Qualified Pension Plans, Defined Benefit [Member]
Reconciliation of change in benefit obligation:
Obligation at January 1	525,100
Obligation at December 31	503,900	525,100
Reconciliation of change in plan assets:
Fair value of plan assets at January 1	373,900
Fair value of plan assets at December 31	399,200	373,900
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(104,700)
Northwest Holdings and Northwest Natural [Member] | Other Postretirement Benefits Plan [Member]
Reconciliation of change in plan assets:
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(27,223)	(29,039)
Defined Benefit Plan, Benefit Obligation, Period Increase (Decrease)	1,800
Northwest Holdings and Northwest Natural [Member] | Pension Plan [Member]
Reconciliation of change in plan assets:
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(143,401)	$ (192,215)
Defined Benefit Plan, Increase in Net Liability	$ 46,500