Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022
Current assets:
Cash and cash equivalents	$ 156,616	$ 29,270	$ 108,556
Accounts receivable	51,999	168,906	50,850
Accrued unbilled revenue	24,626	89,048	16,857
Allowance for uncollectible accounts	(2,312)	(3,296)	(2,171)
Regulatory assets	108,525	117,491	104,830
Derivative instruments	23,454	194,412	62,710
Inventories	94,585	87,096	98,725
Other current assets	49,947	61,286	41,414
Total current assets	507,440	744,213	481,771
Non-current assets:
Property, plant, and equipment	4,468,602	4,261,566	4,207,328
Less: Accumulated depreciation	1,189,968	1,147,166	1,166,150
Total property, plant, and equipment, net	3,278,634	3,114,400	3,041,178
Regulatory assets	312,665	340,432	301,660
Derivative instruments	6,188	5,045	8,008
Other investments	104,562	95,704	96,569
Operating lease right of use asset, net	71,477	73,429	73,145
Assets under sales-type leases	130,952	134,302	135,480
Goodwill	152,399	149,283	74,732
Other non-current assets	100,801	91,518	88,169
Total non-current assets	4,157,678	4,004,113	3,818,941
Total assets	4,665,118	4,748,326	4,300,712
Current liabilities:
Short-term debt	71,000	258,200	141,000
Current maturities of long-term debt	190,728	90,697	50,614
Accounts payable	99,326	180,667	118,274
Taxes accrued	17,120	15,625	18,080
Interest accrued	13,940	10,169	11,086
Regulatory liabilities	88,376	248,582	111,551
Derivative instruments	46,603	28,728	19,594
Operating lease liabilities	1,815	1,514	1,361
Other current liabilities	61,149	64,552	39,796
Total current liabilities	590,057	898,734	511,356
Long-term debt	1,424,572	1,246,167	1,287,006
Deferred credits and other non-current liabilities:
Deferred tax liabilities	375,917	366,022	349,633
Regulatory liabilities	683,262	689,578	663,547
Pension and other postretirement benefit liabilities	145,991	149,143	160,196
Derivative instruments	21,085	20,838	18,824
Operating lease liabilities	77,475	78,965	78,469
Other non-current liabilities	127,219	123,438	110,825
Total deferred credits and other non-current liabilities	1,430,949	1,427,984	1,381,494
Commitments and contingencies (Note 16)
Equity:
Common stock	$ 851,288	$ 805,253	$ 786,094
Shares Authorized (in shares)	100,000,000	100,000,000	100,000,000
Shares outstanding (in shares)	36,575,797	35,524,590	35,098,437
Shares issued (in shares)	36,575,797	35,524,590	35,098,437
Par Value (in dollars per share)	$ 0	$ 0	$ 0
Retained earnings	$ 373,231	$ 376,473	$ 345,570
Accumulated other comprehensive loss	(4,979)	(6,285)	(10,808)
Total equity	1,219,540	1,175,441	1,120,856
Total liabilities and equity	$ 4,665,118	4,748,326	4,300,712
Accounts Payable, Related Party, Type [Extensible Enumeration]	Affiliated Entity [Member]
Other Receivable, after Allowance for Credit Loss, Related Party, Type [Extensible Enumeration]	Affiliated Entity [Member]
Northwest Natural Gas Company [Member]
Current assets:
Cash and cash equivalents	$ 145,073	12,977	11,386
Accounts receivable	48,322	165,607	48,082
Accrued unbilled revenue	22,608	87,482	16,649
Other Receivables, Net, Current	2,195	634	221
Allowance for uncollectible accounts	(2,085)	(3,079)	(2,114)
Regulatory assets	108,525	117,491	104,830
Derivative instruments	22,679	194,236	62,710
Inventories	92,803	86,207	97,633
Other current assets	38,131	57,269	32,605
Total current assets	478,251	718,824	372,002
Non-current assets:
Property, plant, and equipment	4,328,477	4,148,547	4,124,488
Less: Accumulated depreciation	1,175,283	1,137,231	1,157,400
Total property, plant, and equipment, net	3,153,194	3,011,316	2,967,088
Regulatory assets	312,640	340,407	301,596
Derivative instruments	5,430	5,045	8,008
Other investments	87,753	80,110	80,871
Operating lease right of use asset, net	70,852	72,720	73,046
Assets under sales-type leases	130,952	134,302	135,480
Other non-current assets	99,131	89,994	86,661
Total non-current assets	3,859,952	3,733,894	3,652,750
Total assets	4,338,203	4,452,718	4,024,752
Current liabilities:
Short-term debt	0	170,200	53,000
Current maturities of long-term debt	39,997	89,942	49,938
Accounts payable	94,922	177,590	115,066
Accounts Payable, Other, Current	562	9,175	1,789
Taxes accrued	16,915	15,426	17,914
Interest accrued	13,368	8,900	10,533
Regulatory liabilities	88,326	248,553	111,526
Derivative instruments	46,603	28,728	19,594
Operating lease liabilities	1,658	1,363	1,298
Other current liabilities	59,101	62,019	38,998
Total current liabilities	361,452	811,896	419,656
Long-term debt	1,364,556	1,035,935	1,076,533
Deferred credits and other non-current liabilities:
Deferred tax liabilities	366,730	362,353	346,423
Regulatory liabilities	682,315	688,599	662,565
Pension and other postretirement benefit liabilities	145,991	149,143	160,196
Derivative instruments	21,085	20,838	18,824
Operating lease liabilities	77,041	78,345	78,436
Other non-current liabilities	116,930	114,527	109,304
Total deferred credits and other non-current liabilities	1,410,092	1,413,805	1,375,748
Commitments and contingencies (Note 16)
Equity:
Common stock	644,903	614,903	614,903
Retained earnings	563,307	582,593	548,720
Accumulated other comprehensive loss	(6,107)	(6,414)	(10,808)
Total equity	1,202,103	1,191,082	1,152,815
Total liabilities and equity	$ 4,338,203	$ 4,452,718	$ 4,024,752