Northwest Natural Holding (NWN) 10-K 2 Mar 20 2019 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2019	Feb. 24, 2020	Jun. 28, 2019
Document Information [Line Items]
Document Type	10-K
Document Period End Date	Dec. 31, 2019
Entity File Number	1-38681
Document Annual Report	true
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Central Index Key	0001733998
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Registrant Name	NORTHWEST NATURAL HOLDING COMPANY
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	Yes
Entity Common Stock, Shares Outstanding		30,484,008
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Public Float			$ 2,088,864,819
Entity Small Business	false
Entity Emerging Growth Company	false
Document Transition Report	false
Entity Incorporation, State or Country Code	OR
Entity Tax Identification Number	82-4710680
Entity Address, Address Line One	250 S.W. Taylor Street
Entity Address, City or Town	Portland
Entity Address, State or Province	OR
Entity Address, Postal Zip Code	97204
City Area Code	(503)
Local Phone Number	226-4211
Title of 12(b) Security	Common Stock
Trading Symbol	NWN
Security Exchange Name	NYSE
Entity Interactive Data Current	Yes
Entity Shell Company	false
Documents Incorporated by Reference [Text Block]	Portions of Northwest Natural Holding Company's Proxy Statement, to be filed in connection with the 2020 Annual Meeting of Shareholders, are incorporated by reference in Part III.
Northwest Natural Gas Company [Member]
Document Information [Line Items]
Document Type	10-K
Document Period End Date	Dec. 31, 2019
Entity File Number	1-15973
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Central Index Key	0000073020
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Registrant Name	NORTHWEST NATURAL GAS COMPANY
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	No
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Incorporation, State or Country Code	OR
Entity Tax Identification Number	93-0256722
Entity Address, Address Line One	250 S.W. Taylor Street
Entity Address, City or Town	Portland
Entity Address, State or Province	OR
Entity Address, Postal Zip Code	97204
City Area Code	(503)
Local Phone Number	226-4211
Entity Interactive Data Current	Yes
Entity Shell Company	false

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating revenues [Abstract]
Operating revenues	$ 746,372	$ 706,143	$ 755,038
Operating expenses:
Cost of gas	254,911	255,519	324,795
Operations and maintenance	178,191	156,698	152,358
Environmental remediation	12,337	11,127	15,291
General taxes	32,388	32,172	30,639
Revenue taxes	30,325	30,082	0
Depreciation and amortization	91,496	85,156	81,053
Other operating expenses	3,250	3,227	0
Total operating expenses	602,898	573,981	604,136
Income from operations	143,474	132,162	150,902
Other income (expense), net	(22,836)	(3,601)	(295)
Interest expense, net	42,685	37,059	37,526
Income before income taxes	77,953	91,502	113,081
Income tax expense	12,642	24,191	41,008
Net income from continuing operations	65,311	67,311	72,073
Loss from discontinued operations, net of tax	(3,576)	(2,742)	(127,696)
Net income (loss)	61,735	64,569	(55,623)
Other comprehensive income (loss):
Change in employee benefit plan liability, net of taxes of $956 for 2019, ($166) for 2018, and $735 for 2017	(2,655)	476	(2,059)
Amortization of non-qualified employee benefit plan liability, net of taxes of ($172) for 2019, ($278) for 2018, and ($374) for 2017	476	774	572
Comprehensive income (loss)	$ 59,556	$ 65,819	$ (57,110)
Average common shares outstanding:
Basic (in shares)	29,786	28,803	28,669
Diluted (in shares)	29,859	28,873	28,753
Earnings from continuing operations per share of common stock:
Basic (in dollars per share)	$ 2.19	$ 2.34	$ 2.51
Diluted (in dollars per share)	2.19	2.33	2.51
Loss from discontinued operations per share of common stock:
Basic (in dollars per share)	(0.12)	(0.10)	(4.45)
Diluted (in dollars per share)	(0.12)	(0.09)	(4.44)
Earnings (loss) per share of common stock:
Basic (in dollars per share)	2.07	2.24	(1.94)
Diluted (in dollars per share)	$ 2.07	$ 2.24	$ (1.93)
Northwest Natural Gas Company [Member]
Operating revenues [Abstract]
Operating revenues	$ 739,944	$ 705,571	$ 755,038
Operating expenses:
Cost of gas	255,135	255,743	325,019
Utility Operations and maintenance	169,091	155,225	152,180
Environmental remediation	12,337	11,127	15,291
General taxes	32,075	32,086	30,602
Revenue taxes	30,325	30,082	0
Depreciation and amortization	90,405	84,986	81,024
Other operating expenses	3,230	3,223	0
Total operating expenses	592,598	572,472	604,116
Income from operations	147,346	133,099	150,922
Other income (expense), net	(22,968)	(3,599)	(198)
Interest expense, net	41,339	36,992	37,526
Income before income taxes	83,039	92,508	113,198
Income tax expense	14,065	24,459	41,478
Net income from continuing operations	68,974	68,049	71,720
Loss from discontinued operations, net of tax	0	(1,723)	(127,343)
Net income (loss)	68,974	66,326	(55,623)
Other comprehensive income (loss):
Change in employee benefit plan liability, net of taxes of $956 for 2019, ($166) for 2018, and $735 for 2017	(2,655)	476	(2,059)
Amortization of non-qualified employee benefit plan liability, net of taxes of ($172) for 2019, ($278) for 2018, and ($374) for 2017	476	774	572
Comprehensive income (loss)	$ 66,795	$ 67,576	$ (57,110)

Consolidated Statements of Co_2

Consolidated Statements of Comprehensive Income (Parentheticals) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in employee benefit plan liability, net of taxes	$ 956	$ (166)	$ 735
Amortization of non-qualified employee benefit plan liability, net of taxes	(172)	(278)	(374)
Northwest Natural Gas Company [Member]
Change in employee benefit plan liability, net of taxes	956	(166)	735
Amortization of non-qualified employee benefit plan liability, net of taxes	$ (172)	$ (278)	$ (374)

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 9,648	$ 12,633
Accounts receivable	67,137	66,970
Accrued unbilled revenue	56,192	57,827
Allowance for uncollectible accounts	(673)	(977)
Regulatory assets	41,929	41,930
Derivative instruments	6,802	9,001
Inventories	43,985	44,149
Gas reserves	15,278	16,647
Income taxes receivable	256	6,000
Other current assets	38,004	28,472
Discontinued operations - current assets	15,134	13,269
Total current assets	293,692	295,921
Non-current assets:
Property, plant, and equipment	3,476,746	3,414,490
Less: Accumulated depreciation	1,037,847	993,118
Total property, plant, and equipment, net	2,438,899	2,421,372
Gas reserves	48,394	66,197
Regulatory assets	343,146	371,786
Derivative instruments	3,337	725
Other investments	63,333	63,558
Operating lease right of use asset	2,950	0
Assets under sales-type leases	146,310	0
Goodwill	49,929	8,954
Other non-current assets	38,464	14,149
Total non-current assets	3,134,762	2,946,741
Total assets	3,428,454	3,242,662
Current liabilities:
Short-term debt	149,100	217,620
Current maturities of long-term debt	75,109	29,989
Accounts payable	113,370	115,878
Taxes accrued	11,971	11,023
Interest accrued	7,451	7,306
Regulatory liabilities	44,657	47,436
Derivative instruments	2,000	12,381
Operating lease liabilities	2,101	0
Other current liabilities	62,705	54,492
Discontinued operations - current liabilities	13,709	12,959
Total current liabilities	482,173	509,084
Long-term debt	805,955	706,247
Deferred credits and other non-current liabilities:
Deferred tax liabilities	295,643	280,463
Regulatory liabilities	625,717	611,560
Pension and other postretirement benefit liabilities	228,129	221,886
Derivative instruments	609	3,025
Operating lease liabilities	841	0
Other non-current liabilities	123,388	147,763
Total deferred credits and other non-current liabilities	1,274,327	1,264,697
Commitments and contingencies (see Note 17 and Note 18)
Equity:
Common stock - no par value	558,282	457,640
Retained earnings	318,450	312,182
Accumulated other comprehensive loss	(10,733)	(7,188)
Total equity	865,999	762,634
Total liabilities and equity	3,428,454	3,242,662
Northwest Natural Gas Company [Member]
Current assets:
Cash and cash equivalents	5,919	7,947
Accounts receivable	66,823	66,824
Accrued unbilled revenue	56,139	57,773
Receivables from affiliates	787	4,166
Allowance for uncollectible accounts	(672)	(975)
Regulatory assets	41,929	41,930
Derivative instruments	6,802	9,001
Inventories	43,896	44,126
Gas reserves	15,278	16,647
Other current assets	33,258	25,347
Total current assets	270,159	272,786
Non-current assets:
Property, plant, and equipment	3,456,075	3,410,439
Less: Accumulated depreciation	1,036,593	992,855
Total property, plant, and equipment, net	2,419,482	2,417,584
Gas reserves	48,394	66,197
Regulatory assets	343,146	371,786
Derivative instruments	3,337	725
Other investments	49,837	49,922
Operating lease right of use asset	2,760	0
Assets under sales-type leases	146,310	0
Other non-current assets	38,062	13,736
Total non-current assets	3,051,328	2,919,950
Total assets	3,321,487	3,192,736
Current liabilities:
Short-term debt	125,100	217,500
Current maturities of long-term debt	74,907	29,989
Accounts payable	111,641	114,937
Payables to affiliates	1,546	523
Taxes accrued	11,717	10,990
Interest accrued	7,441	7,273
Regulatory liabilities	44,657	47,436
Derivative instruments	2,000	12,381
Operating lease liabilities	1,979	0
Other current liabilities	61,438	53,027
Total current liabilities	442,426	494,056
Long-term debt	769,081	704,134
Deferred credits and other non-current liabilities:
Deferred tax liabilities	309,297	294,739
Regulatory liabilities	625,717	611,560
Pension and other postretirement benefit liabilities	228,129	221,886
Derivative instruments	609	3,025
Operating lease liabilities	772	0
Other non-current liabilities	123,260	147,668
Total deferred credits and other non-current liabilities	1,287,784	1,278,878
Commitments and contingencies (see Note 17 and Note 18)
Equity:
Common stock - no par value	319,557	226,452
Retained earnings	513,372	496,404
Accumulated other comprehensive loss	(10,733)	(7,188)
Total equity	822,196	715,668
Total liabilities and equity	$ 3,321,487	$ 3,192,736

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parentheticals) - $ / shares shares in Thousands, $ / shares in Thousands	Dec. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Par Value (in dollars per share)	$ 0	$ 0
Shares Authorized (in shares)	100,000	100,000
Shares outstanding (in shares)	30,472	28,880
Shares issued (in shares)	30,472	28,880

Consolidated Statement of Share

Consolidated Statement of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock Including APIC [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Northwest Natural Gas Company [Member]	Northwest Natural Gas Company [Member]Common Stock Including APIC [Member]		Northwest Natural Gas Company [Member]Retained Earnings [Member]	Northwest Natural Gas Company [Member]Accumulated Other Comprehensive Income (Loss) [Member]	Northwest Natural Gas Company Consolidated [Member]Northwest Natural Gas Company [Member]
Beginning Balance at Dec. 31, 2016	$ 850,497	$ 445,187	$ 412,261	$ (6,951)		$ 445,187		$ 412,261	$ (6,951)	$ 850,497
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	(57,110)	0	(55,623)	(1,487)	$ (57,110)	0		(55,623)	(1,487)	(57,110)
Dividends on common stock	(54,289)	0	(54,289)	0		0		(54,289)	0	(54,289)
Stock-based compensation	2,882	2,882	0	0		2,882		0	0	2,882
Shares issued pursuant to equity based plans	796	796	0	0		796		0	0	796
Proceeds from Contributions from Parent					0
Ending Balance at Dec. 31, 2017	$ 742,776	448,865	302,349	(8,438)		448,865		302,349	(8,438)	742,776
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends on common stock (in dollars per share)	$ 1.88
Comprehensive income (loss)	$ 65,819	0	64,569	1,250	67,576	0		66,326	1,250	67,576
Dividends on common stock	(54,736)	0	(54,736)	0		0		(41,035)	0	(41,035)
Stock-based compensation	3,020	3,020	0	0		2,161		0	0	2,161
Shares issued pursuant to equity based plans	5,175	5,175	0	0		3,075		0	0	3,075
Proceeds from Contributions from Parent					0
Cash purchase of shares for business combination	(7,945)	(7,945)	0	0
Value of shares transferred for business combination	8,525	8,525	0	0
Ending Balance at Dec. 31, 2018	$ 762,634	457,640	312,182	(7,188)		226,452		496,404	(7,188)	715,668
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends on common stock (in dollars per share)	$ 1.89
Transfer from Investments						(227,649)		168,764	0	(58,885)
Comprehensive income (loss)	$ 59,556	0	61,735	(2,179)	66,795	0		68,974	(2,179)	66,795
Dividends on common stock	(56,833)	0	(56,833)	0		0		(53,372)	0	(53,372)
Stock-based compensation	2,601	2,601	0	0
Shares issued pursuant to equity based plans	5,085	5,085	0	0
Proceeds from Contributions from Parent					$ 93,155	93,105	[1]	0	0	93,105
Issuance of common stock, net of issuance costs	92,956	92,956	0	0
Reclassification of tax effects from the TCJA	0	0	1,366	(1,366)		0		(1,366)	1,366	0
Ending Balance at Dec. 31, 2019	$ 865,999	$ 558,282	$ 318,450	$ (10,733)		$ 319,557		$ 513,372	$ (10,733)	$ 822,196
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends on common stock (in dollars per share)	$ 1.90
[1]	Stock-based compensation is based on stock awards of NW Natural to be issued in shares of NW Holdings.

Consolidated Statement of Cash

Consolidated Statement of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating activities:
Net income (loss)	$ 61,735	$ 64,569	$ (55,623)
Adjustments to reconcile net income (loss) to cash provided by operations:
Depreciation and amortization	91,496	85,156	81,053
Regulatory amortization of gas reserves	19,172	16,684	16,353
Deferred income taxes	6,317	14,356	(52,414)
Qualified defined benefit pension plan expense	16,497	8,108	5,364
Contributions to qualified defined benefit pension plans	(10,970)	(15,540)	(19,430)
Deferred environmental expenditures, net	(16,226)	(14,528)	(13,716)
Environmental remediation expense	12,337	11,127	15,291
Regulatory revenue deferral from the TCJA	853	7,929	0
Regulatory disallowance of pension costs	10,500	0	0
Other	(13,907)	(1,596)	(2,102)
Changes in assets and liabilities:
Receivables, net	5,844	181	3,282
Inventories	(5,969)	3,207	5,600
Income and other taxes	4,528	(16,904)	6,734
Accounts payable	(16,485)	16,792	1,092
Interest accrued	145	526	807
Deferred gas costs	(23,471)	(14,395)	17,122
Decoupling mechanism	18,661	4,497	4,436
Other, net	(4,285)	(3,945)	(8,529)
Discontinued operations	712	(645)	197,180
Cash provided by operating activities	185,298	168,771	206,704
Investing activities:
Capital expenditures	(223,471)	(214,636)	(213,325)
Acquisitions, net of cash acquired	(56,786)	(873)	0
Leasehold improvement expenditures	(18,812)	(4,415)	0
Other	(2,885)	1,898	(577)
Discontinued operations	(1,827)	573	(270)
Cash used in investing activities	(303,781)	(217,453)	(214,172)
Financing activities:
Repurchases related to stock-based compensation	0	0	(2,034)
Proceeds from stock options exercised	2,015	1,546	4,819
Proceeds from common stock issued	92,956	0	0
Long-term debt issued	175,000	50,000	100,000
Long-term debt retired	(30,000)	(97,000)	(40,000)
Change in short-term debt	(68,520)	163,274	900
Cash dividend payments on common stock	(53,339)	(51,311)	(53,957)
Stock purchases related to acquisitions	0	(7,951)	0
Other	(2,614)	(715)	(2,309)
Cash provided by financing activities	115,498	57,843	7,419
Increase (decrease) in cash and cash equivalents	(2,985)	9,161	(49)
Cash and cash equivalents, beginning of period	12,633	3,472	3,521
Cash and cash equivalents, end of period	9,648	12,633	3,472
Supplemental disclosure of cash flow information:
Interest paid, net of capitalization	41,231	35,324	34,787
Income taxes paid (refunded)	(96)	27,370	14,780
Northwest Natural Gas Company [Member]
Operating activities:
Net income (loss)	68,974	66,326	(55,623)
Adjustments to reconcile net income (loss) to cash provided by operations:
Depreciation and amortization	90,405	84,986	81,024
Regulatory amortization of gas reserves	19,172	16,684	16,353
Deferred income taxes	4,046	12,330	15,894
Qualified defined benefit pension plan expense	16,497	8,108	5,364
Contributions to qualified defined benefit pension plans	(10,970)	(15,540)	(19,430)
Deferred environmental expenditures, net	(16,226)	(14,528)	(13,716)
Environmental remediation expense	12,337	11,127	15,291
Regulatory revenue deferral from the TCJA	853	7,929	0
Regulatory disallowance of pension costs	10,500	0	0
Other	(12,317)	(883)	(2,003)
Changes in assets and liabilities:
Receivables, net	9,264	(3,920)	3,215
Inventories	(5,990)	3,212	5,601
Income and other taxes	496	(7,854)	6,730
Accounts payable	(18,548)	13,937	3,332
Interest accrued	168	500	807
Deferred gas costs	(23,471)	(14,395)	17,122
Decoupling mechanism	18,661	4,497	4,436
Other, net	(2,309)	(3,958)	(8,291)
Discontinued operations	0	3,184	126,371
Cash provided by operating activities	186,176	173,508	206,483
Investing activities:
Capital expenditures	(221,380)	(214,328)	(213,325)
Leasehold improvement expenditures	(18,812)	(4,415)	0
Other	(2,885)	898	(577)
Discontinued operations	0	(20,617)	(270)
Cash used in investing activities	(243,077)	(238,462)	(214,172)
Financing activities:
Repurchases related to stock-based compensation	0	0	(2,034)
Proceeds from stock options exercised	0	1,368	4,819
Long-term debt issued	140,000	50,000	100,000
Long-term debt retired	(30,000)	(97,000)	(40,000)
Change in short-term debt	(92,400)	163,300	900
Proceeds from Contributions from Parent	93,155	0	0
Cash dividend payments on common stock	(53,372)	(38,387)	(53,957)
Other	(2,510)	(1,539)	(2,309)
Discontinued operations	0	(7,951)	0
Cash provided by financing activities	54,873	69,791	7,419
Increase (decrease) in cash and cash equivalents	(2,028)	4,837	(270)
Cash and cash equivalents, beginning of period	7,947	3,110	3,380
Cash and cash equivalents, end of period	5,919	7,947	3,110
Supplemental disclosure of cash flow information:
Interest paid, net of capitalization	39,927	35,305	34,787
Income taxes paid (refunded)	$ 2,479	$ 27,350	$ 14,780

Organization and Principles of

Organization and Principles of Consolidation	12 Months Ended
	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block]	ORGANIZATION AND PRINCIPLES OF CONSOLIDATION On October 1, 2018, we completed a reorganization into a holding company structure. In this reorganization, shareholders of NW Natural (the predecessor publicly held parent company) became shareholders of NW Holdings on a one-for-one basis; maintaining the same number of shares and ownership percentage as held in NW Natural immediately prior to the reorganization. NW Natural became a wholly-owned subsidiary of NW Holdings. Additionally, certain subsidiaries of NW Natural were transferred to NW Holdings. This reorganization was accounted for as a transaction among entities under common control. As required under accounting guidance, these subsidiaries are presented in this report as discontinued operations in the consolidated results of NW Natural. See Note 19 for additional information. The accompanying consolidated financial statements represent the respective, consolidated financial results of NW Holdings and NW Natural and all respective companies that each registrant directly or indirectly controls, either through majority ownership or otherwise. This is a combined report of NW Holdings and NW Natural, which includes separate consolidated financial statements for each registrant. NW Natural's regulated natural gas distribution activities are reported in the natural gas distribution (NGD) segment. The NGD segment is NW Natural's core operating business and serves residential, commercial, and industrial customers in Oregon and southwest Washington. The NGD segment is the only reportable segment for NW Holdings and NW Natural. All other activities, water businesses, and other investments are aggregated and reported as other at their respective registrant. In addition, NW Holdings has reported discontinued operations results related to the pending sale of Gill Ranch Storage, LLC (Gill Ranch). All prior period amounts have been retrospectively adjusted to reflect this change both in operational results and reportable segments for NW Holdings and NW Natural, respectively. These reclassifications and the reorganization activities described above had no effect on the prior year’s consolidated results of operations, financial condition, or cash flows. See Note 19 for additional information. NW Holdings' direct and indirect wholly-owned subsidiaries as of the filing date of this report include: • Northwest Natural Gas Company (NW Natural); • Northwest Energy Corporation (Energy Corp); • NWN Gas Reserves LLC (NWN Gas Reserves); • NW Natural Energy, LLC (NWN Energy); • NW Natural Gas Storage, LLC (NWN Gas Storage); • Gill Ranch Storage, LLC (Gill Ranch), which is presented as a discontinued operation; • NNG Financial Corporation (NNG Financial); • KB Pipeline Company (KB); • NW Natural Water Company, LLC (NWN Water); • Falls Water Co., Inc. (Falls Water); • Salmon Valley Water Company; • NW Natural Water of Oregon, LLC (NWN Water of Oregon); • Sunstone Water, LLC; • Sunstone Infrastructure, LLC; • Sunriver Water, LLC (Sunriver Water); • Sunriver Environmental, LLC (Sunriver Environmental); • NW Natural Water of Washington, LLC (NWN Water of Washington); • Cascadia Water, LLC (Cascadia Water); • Cascadia Infrastructure, LLC; ▪ Suncadia Water Company, LLC (Suncadia Water); ▪ Suncadia Environmental Company, LLC (Suncadia Environmental); • NW Natural Water of Idaho, LLC (NWN Water of Idaho); • Gem State Water Company, LLC (Gem State Water); • Gem State Infrastructure, LLC; and • NW Natural Water of Texas, LLC (NWN Water of Texas); • Blue Topaz Water, LLC; and • Blue Topaz Infrastructure, LLC. Investments in corporate joint ventures and partnerships that NW Holdings does not directly or indirectly control, and for which it is not the primary beneficiary, include NNG Financial's investment in Kelso-Beaver Pipeline and NWN Energy's investment in Trail West Holdings, LLC (TWH), which are accounted for under the equity method. NW Holdings and its direct and indirect subsidiaries are collectively referred to herein as NW Holdings, and NW Natural and its direct and indirect subsidiaries are collectively referred to herein as NW Natural. The consolidated financial statements of NW Holdings and NW Natural are presented after elimination of all intercompany balances and transactions. During the second quarter of 2018, we moved forward with our long-term strategic plans, which include a shift away from the California gas storage business. In June 2018, NWN Gas Storage, a wholly-owned subsidiary of NW Natural at the time and now a wholly-owned subsidiary of NW Holdings, entered into a Purchase and Sale Agreement that provides for the sale of all of the membership interests in its wholly-owned subsidiary, Gill Ranch. We received regulatory approval for the sale in December 2019. We have concluded that the pending sale of Gill Ranch qualifies as assets and liabilities held for sale and discontinued operations. As such, the results of Gill Ranch have been presented as a discontinued operation for NW Holdings for all periods presented and for NW Natural up until the holding company reorganization was effective on October 1, 2018 on the consolidated statements of comprehensive income and cash flows, and the assets and liabilities associated with Gill Ranch have been classified as discontinued operations assets and liabilities on the NW Holdings consolidated balance sheet. See Note 19 for additional information. Additionally, we reevaluated reportable segments and concluded that the remaining gas storage activities no longer met the requirements to be separately reported as a segment. Interstate Storage Services is now reported in Other under NW Natural and NW Holdings as applicable, and all prior periods reflect this change. See Note 4 , which provides segment information. Notes to the consolidated financial statements reflect the activity of continuing operations for both NW Holdings and NW Natural for all periods presented, unless otherwise noted.

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Significant Accounting Policies	SIGNIFICANT ACCOUNTING POLICIES Use of Estimates The preparation of financial statements in conformity with generally accepted accounting principles in the United States of America (U.S. GAAP) requires management to make estimates and assumptions that affect reported amounts in the consolidated financial statements and accompanying notes. Actual amounts could differ from those estimates, and changes would most likely be reported in future periods. Management believes the estimates and assumptions used are reasonable . Industry Regulation NW Holdings' principal business is to operate as a holding company for NW Natural and its other subsidiaries. NW Natural's principal business is the distribution of natural gas, which is regulated by the OPUC and WUTC. NW Natural also has natural gas storage services, which are regulated by the FERC, and to a certain extent by the OPUC and WUTC. Additionally, certain of NW Holdings' subsidiaries own water businesses, which are regulated by the public utility commission in the state in which the water utility is located, which is currently Oregon, Washington and Idaho. Accounting records and practices of the regulated businesses conform to the requirements and uniform system of accounts prescribed by these regulatory authorities in accordance with U.S. GAAP. The businesses in which customer rates are regulated by the OPUC, WUTC, IPUC, and FERC have approved cost-based rates which are intended to allow such businesses to earn a reasonable return on invested capital. In applying regulatory accounting principles, NW Holdings and NW Natural capitalize or defer certain costs and revenues as regulatory assets and liabilities pursuant to orders of the applicable state public utility commission, which provide for the recovery of revenues or expenses from, or refunds to, utility customers in future periods, including a return or a carrying charge in certain cases. Amounts NW Natural deferred as regulatory assets and liabilities were as follows: Regulatory Assets In thousands 2019 2018 Current: Unrealized loss on derivatives (1) $ 2,000 $ 12,381 Gas costs 20,140 2,873 Environmental costs (2) 4,762 5,601 Decoupling (3) 1,969 9,140 Pension balancing (4) 5,939 — Income taxes 2,209 2,218 Other (5) 4,910 9,717 Total current $ 41,929 $ 41,930 Non-current: Unrealized loss on derivatives (1) $ 609 $ 3,025 Pension balancing (4) 48,251 74,173 Income taxes 17,173 19,185 Pension and other postretirement benefit liabilities 173,262 174,993 Environmental costs (2) 87,624 76,149 Gas costs 2,866 9,978 Decoupling (3) — 2,545 Other (5) 13,361 11,738 Total non-current $ 343,146 $ 371,786 Regulatory Liabilities In thousands 2019 2018 Current: Gas costs $ 1,223 $ 17,182 Unrealized gain on derivatives (1) 6,622 8,740 Decoupling (3) 4,831 2,264 Income taxes (6) 8,435 — Other (5) 23,546 19,250 Total current $ 44,657 $ 47,436 Non-current: Gas costs $ 2,013 $ 552 Unrealized gain on derivatives (1) 3,337 725 Decoupling (3) 6,378 — Income taxes (6) 198,219 225,408 Accrued asset removal costs (7) 401,893 380,464 Other (5) 13,877 4,411 Total non-current $ 625,717 $ 611,560 (1) Unrealized gains or losses on derivatives are non-cash items and, therefore, do not earn a rate of return or a carrying charge. These amounts are recoverable through natural gas distribution rates as part of the annual Purchased Gas Adjustment (PGA) mechanism when realized at settlement. (2) Refer to the Environmental Cost Deferral and Recovery table in Note 18 for a description of environmental costs. (3) This deferral represents the margin adjustment resulting from differences between actual and expected volumes. (4) Refer to Note 10 for information regarding the deferral of pension expenses. (5) Balances consist of deferrals and amortizations under approved regulatory mechanisms and typically earn a rate of return or carrying charge. (6) This balance represents estimated amounts associated with the Tax Cuts and Jobs Act. See Note 11 . (7) Estimated costs of removal on certain regulated properties are collected through rates. See "Accounting Policies— Plant, Property, and Accrued Asset Removal Costs " below. The amortization period for NW Natural's regulatory assets and liabilities ranges from less than one year to an indeterminable period. Regulatory deferrals for gas costs payable are generally amortized over 12 months beginning each November 1 following the gas contract year during which the deferred gas costs are recorded. Similarly, most other regulatory deferred accounts are amortized over 12 months . However, certain regulatory account balances, such as income taxes, environmental costs, pension liabilities, and accrued asset removal costs, are large and tend to be amortized over longer periods once NW Natural has agreed upon an amortization period with the respective regulatory agency. We believe all costs incurred and deferred at December 31, 2019 are prudent. All regulatory assets and liabilities are reviewed annually for recoverability, or more often if circumstances warrant. If we should determine that all or a portion of these regulatory assets or liabilities no longer meet the criteria for continued application of regulatory accounting, then NW Natural would be required to write-off the net unrecoverable balances in the period such determination is made. Regulatory interest income of $19.6 million and $7.6 million and regulatory interest expense of $12.3 million and $5.9 million was recognized within other income (expense), net for the years ended December 31, 2019 and 2018 , respectively. Environmental Regulatory Accounting See Note 18 for information about the SRRM and OPUC orders regarding implementation. New Accounting Standards NW Natural and NW Holdings consider the applicability and impact of all accounting standards updates (ASUs) issued by the Financial Accounting Standards Board (FASB). ASUs not listed below were assessed and determined to be either not applicable or are expected to have minimal impact on consolidated financial position or results of operations. Recently Adopted Accounting Pronouncements ACCUMULATED OTHER COMPREHENSIVE INCOME. On February 14, 2018, the FASB issued ASU 2018-02, "Income Statement—Reporting Comprehensive Income: Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income." This update was issued in response to concerns from certain stakeholders regarding the current requirements under U.S. GAAP that deferred tax assets and liabilities are adjusted for a change in tax laws or rates, and the effect is to be included in income from continuing operations in the period of the enactment date. This requirement is also applicable to items in accumulated other comprehensive income where the related tax effects were originally recognized in other comprehensive income. The adjustment of deferred taxes due to the new corporate income tax rate enacted through the Tax Cuts and Jobs Act (TCJA) on December 22, 2017 recognized in income from continuing operations causes the tax effects of items within accumulated other comprehensive income (referred to as stranded tax effects) to not reflect the appropriate tax rate. The amendments in this update allow but do not require a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the TCJA and require certain disclosures about stranded tax effects. NW Natural adopted and applied the standard in the first quarter of 2019. NW Natural elected to reclassify the stranded tax effects of the TCJA of $1.4 million from accumulated other comprehensive loss to retained earnings in the period of adoption. Going forward, our policy is that, in the event that regulation changes result in stranded tax effects, such amounts will be reclassified from accumulated other comprehensive income (loss) to retained earnings in the final period that the related deferred tax balance remeasurement is expected to impact income from continuing operations. DERIVATIVES AND HEDGING. On August 28, 2017, the FASB issued ASU 2017-12, "Derivatives and Hedging: Targeted Improvements to Accounting for Hedging Activities." The purpose of the amendment is to more closely align hedge accounting with companies’ risk management strategies. The ASU amends the accounting for risk component hedging, the hedged item in fair value hedges of interest rate risk, and amounts excluded from the assessment of hedge effectiveness. The guidance also amends the recognition and presentation of the effect of hedging instruments and includes other simplifications of hedge accounting. The amendments in this update were effective beginning January 1, 2019 and were applied prospectively to hedging instruments. The adoption did not have an impact on the financial statements or disclosures of NW Holdings or NW Natural. GOODWILL. On January 26, 2017, the FASB issued ASU 2017-04, "Simplifying the Test for Goodwill Impairment." The ASU removes Step 2 from the goodwill impairment test and under the amended guidance an entity should perform its annual goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount and recognize an impairment charge for the amount in which the carrying amounts exceed the fair value of the reporting unit. The amendments in this standard are effective for us beginning January 1, 2020 and early adoption is permitted for interim or annual goodwill impairment tests performed after January 1, 2017. NW Natural early adopted ASU 2017-04 in the quarter ended September 30, 2018. The adoption of this ASU did not materially affect the financial statements and disclosures of NW Holdings or NW Natural. LEASES. On February 25, 2016, the FASB issued ASU 2016-02, "Leases," which revises the existing lease accounting guidance. Pursuant to the new standard (“ASC 842”), lessees are required to recognize all leases, including operating leases that are greater than 12 months at lease commencement, on the balance sheet and record corresponding right of use assets and lease liabilities. Lessor accounting will remain substantially the same under the new standard. Quantitative and qualitative disclosures are also required for users of the financial statements to have a clear understanding of the nature of our leasing activities. We elected the alternative prospective transition approach for adoption beginning January 1, 2019. All comparative periods prior to January 1, 2019 will retain the financial reporting and disclosure requirements of ASC 840 “Leases” (“ASC 840”). There was no cumulative effect adjustment to the opening balance of retained earnings recorded as of January 1, 2019 for adoption as there were no initial direct costs or other capitalized costs related to the legacy leases that needed to be derecognized upon adoption of ASC 842. We elected the land easement optional practical expedient to not evaluate existing or expired land easements that were not previously accounted for as leases under the ASC 840 lease guidance. For the existing lease portfolio, we did not elect the optional practical expedient package to retain the legacy lease accounting conclusions upon adoption; we re-assessed our existing contracts under the new leasing standard including whether the contract meets the definition of a lease and lease classification. As a result, we determined that most of our underground gas storage contracts no longer meet the definition of a lease under the new lease standard. In October 2017, NW Natural entered into a 20-year operating lease agreement commencing in 2020 for a new corporate operations center location in Portland, Oregon. The lease was analyzed under ASC 840 in consideration of build-to-suit lease accounting guidance with the conclusion that NW Natural was the owner of the asset during construction for accounting purposes. Under the new lease standard, ASC 842, NW Natural is no longer considered the owner of the asset during construction for accounting purposes. As such, in January 2019 we derecognized the build-to-suit asset and liability balances of $26.0 million as of December 31, 2018 that were previously recorded within property, plant and equipment and other non-current liabilities in the consolidated balance sheet. Upon adoption on January 1, 2019, NW Holdings recorded an operating lease right of use asset and an associated operating lease liability of approximately $7.3 million , of which $7.0 million was recorded at NW Natural. Lease liabilities are measured using NW Natural's incremental borrowing rate based on information available at the lease commencement date in determining the present value of lease payments. As of December 31, 2019 , our lessee portfolio under the new standard consists primarily of our current leased corporate operations center, which expires in 2020. Our lessor portfolio primarily consists of our North Mist Facility which classified as a sales-type lease. See Note 7 for more information. CLOUD COMPUTING. On August 29, 2018, the FASB issued ASU 2018-15, "Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract." The purpose of the amendment is to align the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. The amendments in this update are effective for us beginning January 1, 2020. Early adoption is permitted, and NW Holdings and NW Natural early adopted ASU 2018-15 in the quarter ended March 31, 2019 utilizing the prospective application methodology. The adoption of this ASU did not materially affect the financial statements and disclosures of NW Holdings or NW Natural. Recently Issued Accounting Pronouncements INCOME TAXES. On December 18, 2019, the FASB issued ASU 2019-12, "Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes." The purpose of the amendment is to reduce cost and complexity related to accounting for income taxes by removing certain exceptions to the general principles and improving consistent application for other areas in Topic 740. The amendments in this update are effective for us beginning January 1, 2021. Early adoption is permitted. The amended presentation and disclosure guidance should be applied retrospectively. We do not expect this ASU to materially affect the financial statements and disclosures of NW Holdings or NW Natural. RETIREMENT BENEFITS. On August 28, 2018, the FASB issued ASU 2018-14, "Changes to the Disclosure Requirements for Defined Benefit Plans." The purpose of the amendment is to modify the disclosure requirements for defined benefit pension and other postretirement plans. The amendments in this update are effective for us beginning January 1, 2020. Early adoption is permitted. The amended presentation and disclosure guidance should be applied retrospectively. We do not expect this ASU to materially affect the financial statements and disclosures of NW Holdings or NW Natural. FAIR VALUE MEASUREMENT. On August 28, 2018, the FASB issued ASU 2018-13, "Changes to the Disclosure Requirements for Fair Value Measurement." The purpose of the amendment is to modify the disclosure requirements for fair value measurements. The amendments in this update are effective for us beginning January 1, 2020. Early adoption is permitted. The amendments on changes in unrealized gains and losses, the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements and the narrative description of measurement uncertainty should be applied prospectively. All other amendments should be applied retrospectively. NW Holdings and NW Natural do not have either Level 3 fair value measurements or transfers between Level 1 or Level 2 in their current portfolios, and therefore, we do not expect this ASU to have an impact on the financial statements and disclosures of NW Holdings or NW Natural. CREDIT LOSSES. On June 16, 2016, the FASB issued ASU 2016-13, "Measurement of Credit Losses on Financial Instruments," which applies to financial assets subject to credit losses and measured at amortized cost. The new standard will require financial assets measured at amortized cost to be presented at the net amount expected to be collected and the allowance for credit losses is to be recorded as a valuation account that is deducted from the amortized cost basis. The amendments in this update are effective beginning January 1, 2020. Early adoption is permitted for fiscal years beginning after December 15, 2018. The majority of NW Holdings' and NW Natural's financial assets are short-term in nature, such as trade receivables, and therefore, we do not expect this ASU to materially affect our financial statements and disclosures. Accounting Policies The accounting policies discussed below apply to both NW Holdings and NW Natural. Plant, Property, and Accrued Asset Removal Costs Plant and property are stated at cost, including capitalized labor, materials, and overhead. In accordance with regulatory accounting standards, the cost of acquiring and constructing long-lived plant and property generally includes an allowance for funds used during construction (AFUDC) or capitalized interest. AFUDC represents the regulatory financing cost incurred when debt and equity funds are used for construction (see “ AFUDC ” below). When constructed assets are subject to market-based rates rather than cost-based rates, the financing costs incurred during construction are included in capitalized interest in accordance with U.S. GAAP, not as regulatory financing costs under AFUDC. In accordance with long-standing regulatory treatment, our depreciation rates consist of three components: one based on the average service life of the asset, a second based on the estimated salvage value of the asset, and a third based on the asset’s estimated cost of removal. We collect, through rates, the estimated cost of removal on certain regulated properties through depreciation expense, with a corresponding offset to accumulated depreciation. These removal costs are non-legal obligations as defined by regulatory accounting guidance. Therefore, we have included these costs as non-current regulatory liabilities rather than as accumulated depreciation on our consolidated balance sheets. In the rate setting process, the liability for removal costs is treated as a reduction to the net rate base on which the NGD business has the opportunity to earn its allowed rate of return. The costs of NGD plant retired or otherwise disposed of are removed from NGD plant and charged to accumulated depreciation for recovery or refund through future rates. Gains from the sale of regulated assets are generally deferred and refunded to customers. For assets not related to NGD, we record a gain or loss upon the disposal of the property, and the gain or loss is recorded in operating income or loss in the consolidated statements of comprehensive income. The provision for depreciation of NGD property, plant, and equipment is recorded under the group method on a straight-line basis with rates computed in accordance with depreciation studies approved by regulatory authorities. The weighted-average depreciation rate for NGD assets in service was approximately 2.9 % for 2019 , and 2.8% for 2018 , and 2017 , reflecting the approximate weighted-average economic life of the property. This includes 2019 weighted-average depreciation rates for the following asset categories: 2.6 % for transmission and distribution plant, 2.2 % for gas storage facilities, 5.7 % for general plant, and 4.7 % for intangible and other fixed assets. AFUDC. Certain additions to NGD plant include AFUDC, which represents the net cost of debt and equity funds used during construction. AFUDC is calculated using actual interest rates for debt and authorized rates for ROE, if applicable. If short-term debt balances are less than the total balance of construction work in progress, then a composite AFUDC rate is used to represent interest on all debt funds, shown as a reduction to interest charges, and on ROE funds, shown as other income. While cash is not immediately recognized from recording AFUDC, it is realized in future years through rate recovery resulting from the higher NGD cost of service. Our composite AFUDC rate was 3.9 % in 2019 , 5.2 % in 2018 , and 5.5 % in 2017 . IMPAIRMENT OF LONG-LIVED ASSETS. We review the carrying value of long-lived assets whenever events or changes in circumstances indicate the carrying amount of the assets may not be recoverable. Factors that would necessitate an impairment assessment of long-lived assets include a significant adverse change in the extent or manner in which the asset is used, a significant adverse change in legal factors or business climate that could affect the value of the asset, or a significant decline in the observable market value or expected future cash flows of the asset, among others. When such factors are present, we assess the recoverability by determining whether the carrying value of the asset will be recovered through expected future cash flows. An asset is determined to be impaired when the carrying value of the asset exceeds the expected undiscounted future cash flows from the use and eventual disposition of the asset. If an impairment is indicated, we record an impairment loss for the difference between the carrying value and the fair value of the long-lived assets. Fair value is estimated using appropriate valuation methodologies, which may include an estimate of discounted cash flows. In the fourth quarter of 2017, a non-cash pre-tax impairment of long-lived assets at the Gill Ranch Facility of $192.5 million was recognized. The income approach was used to estimate fair value, using the estimated future net cash flows. We also compared the results of the income approach to our own recent sale experience and recent market comparable transactions in order to estimate fair value. The Gill Ranch Facility was originally included in the gas storage segment, which has since been eliminated, and is now included in discontinued operations. We determined circumstances existed that indicated the carrying value of the assets may not be recoverable. Those circumstances included the completion of a comprehensive strategic review process that evaluated various alternatives including a potential sale, as well as contracting for available storage at lower than anticipated values for the coming storage year. Given these considerations, management re-evaluated the estimated cash flows from our interests in the Gill Ranch Facility, and determined that those estimated cash flows were no longer sufficient to cover the carrying value of the assets. The results of Gill Ranch have been presented as a discontinued operation for NW Holdings and NW Natural on the consolidated statements of comprehensive income and cash flows, and the assets and liabilities associated with Gill Ranch have been classified as discontinued operations assets and liabilities on the consolidated balance sheets. See Note 19 for additional information. Cash and Cash Equivalents For purposes of reporting cash flows, cash and cash equivalents include cash on hand plus highly liquid investment accounts with original maturity dates of three months or less. At December 31, 2019 and 2018 , NW Holdings had outstanding checks of approximately $ 3.2 million and $ 2.7 million , respectively, substantially all of which is recorded at NW Natural. These balances are included in accounts payable in the NW Holdings and NW Natural balance sheets. Revenue Recognition and Accrued Unbilled Revenue Revenues, derived primarily from the sale and transportation of natural gas, are recognized upon delivery of the gas commodity or service to customers. Revenues include accruals for gas or water delivered but not yet billed to customers based on estimates of deliveries from meter reading dates to month end (accrued unbilled revenue). Accrued unbilled revenue is dependent upon a number of factors that require management’s judgment, including total natural gas receipts and deliveries, customer use of natural gas or water by billing cycle, and weather factors. Accrued unbilled revenue is reversed the following month when actual billings occur. NW Holdings' accrued unbilled revenue at December 31, 2019 and 2018 was $56.2 million and $57.8 million respectively, substantially all of which is accrued unbilled revenue at NW Natural. Revenues not related to NGD are derived primarily from Interstate Storage Services, asset management activities at the Mist gas storage facility, and other investments and business activities. At the Mist underground storage facility, revenues are primarily firm service revenues in the form of fixed monthly reservation charges. In addition, we also have asset management service revenue from an independent energy marketing company that optimizes commodity, storage, and pipeline capacity release transactions. Under this agreement, guaranteed asset management revenue is recognized using a straight-line, pro-rata methodology over the term of each contract. Revenues earned above the guaranteed amount are recognized as they are earned. Revenue Taxes Revenue-based taxes are primarily franchise taxes, which are collected from customers and remitted to taxing authorities. In 2018, revenue taxes are included in operating expenses in the statements of comprehensive income for NW Holdings and NW Natural. In 2017 and 2016, revenue taxes are included in operating revenues in the statements of comprehensive income for NW Holdings and NW Natural. All revenue taxes are recorded at NW Natural and were $30.3 million , $30.1 million , and $19.1 million for 2019 , 2018 , and 2017 , respectively. Accounts Receivable and Allowance for Uncollectible Accounts Accounts receivable consist primarily of amounts due for natural gas sales and transportation services to NGD customers, plus amounts due for gas storage services. At NW Holdings and NW Natural we establish allowances for uncollectible accounts (allowance) for trade receivables, including accrued unbilled revenue, based on the aging of receivables, collection experience of past due account balances including payment plans, and historical trends of write-offs as a percent of revenues. A specific allowance is established and recorded for large individual customer receivables when amounts are identified as unlikely to be partially or fully recovered. Inactive accounts are written-off against the allowance after they are 120 days past due or when deemed uncollectible. Differences between the estimated allowance and actual write-offs will occur based on a number of factors, including changes in economic conditions, customer creditworthiness, and natural gas prices. The allowance for uncollectible accounts is adjusted quarterly, as necessary, based on information currently available. Inventories NGD gas inventories, which consist of natural gas in storage for NGD customers, are stated at the lower of weighted-average cost or net realizable value. The regulatory treatment of these inventories provides for cost recovery in customer rates. NGD gas inventories injected into storage are priced in inventory based on actual purchase costs, and those withdrawn from storage are charged to cost of gas during the period they are withdrawn at the weighted-average inventory cost. Gas storage inventories, which primarily represent inventories at the Gill Ranch Facility and are included in Discontinued operations - current assets on the consolidated balance sheets, mainly consist of natural gas received as fuel-in-kind from storage customers. Gas storage inventories are valued at the lower of average cost or net realizable value. Cushion gas is not included in inventory balances, is recorded at original cost, and is classified as a long-term plant asset. Materials and supplies inventories consist of inventories both related to and unrelated to NGD and are stated at the lower of average cost or net realizable value. NW Natural's NGD and gas storage inventories totaled $ 27.5 million and $ 29.9 million at 2019 and 2018 , respectively. At December 31, 2019 and 2018 , NW Holdings' materials and supplies inventories, which are comprised primarily of NW Natural's materials and supplies, totaled $ 16.5 million and $ 14.2 million , respectively. Gas Reserves Gas reserves are payments to acquire and produce natural gas reserves. Gas reserves are stated at cost, adjusted for regulatory amortization, with the associated deferred tax benefits recorded as liabilities on the balance sheet. The current portion is calculated based on expected gas deliveries within the next fiscal year. NW Natural recognizes regulatory amortization of this asset on a volumetric basis calculated using the estimated gas reserves and the estimated therms extracted and sold each month. The amortization of gas reserves is recorded to cost of gas along with gas production revenues and production costs. See Note 13 . Derivatives NW Natural's derivatives are measured at fair value and recognized as either assets or liabilities on the balance sheet. Changes in the fair value of the derivatives are recognized in earnings unless specific regulatory or hedge accounting criteria are met. Accounting for derivatives and hedges provides an exception for contracts intended for normal purchases and normal sales for which physical delivery is probable. In addition, certain derivative contracts are approved by regulatory authorities for recovery or refund through customer rates. Accordingly, the changes in fair value of these approved contracts are deferred as regulatory assets or liabilities pursuant to regulatory accounting principles. NW Natural's financial derivatives generally qualify for deferral under regulatory accounting. NW Natural's index-priced physical derivative contracts also qualify for regulatory deferral accounting treatment. Derivative contracts entered into for NGD requirements after the annual PGA rate has been set and maturing during the PGA year are subject to the PGA incentive sharing mechanism. In Oregon, NW Natural participates in a PGA sharing mechanism under which it is required to select either an 80% or 90% deferral of higher or lower gas costs such that the impact on current earnings from the gas cost sharing is either 20% or 10% of gas cost differences compared to PGA prices, respectively. For each of the PGA years in Oregon beginning November 1, 2019 , 2018 , and 2017 , NW Natural selected the 90% deferral of gas cost differences. In Washington, 100% of the differences between the PGA prices and actual gas costs are deferred. See Note 16 . NW Natural's financial derivatives policy sets forth the guidelines for using selected derivative products to support prudent risk management strategies within designated parameters. NW Natural's objective for using derivatives is to decrease the volatility of gas prices and cash flows without speculative risk. The use of derivatives is permitted only after the risk exposures have been identified, are determined not to exceed acceptable tolerance levels, and are determined necessary to support normal business activities. NW Natural does not enter into derivative instruments for trading purposes. All derivatives for NW Holdings are currently held at NW Natural. Fair Value In accordance with fair value accounting, we use the following fair value hierarchy for determining inputs for our debt, pension plan assets, and derivative fair value measurements: • Level 1: Valuation is based on quoted prices for identical instruments traded in active markets; • Level 2: Valuation is based on quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model-based valuation techniques for which all significant assumptions are observable in the market; and • Level 3: Valuation is generated from model-based techniques that use significant assumptions not observable in the market. These unobservable assumptions reflect our own estimates of assumptions market participants would use in valuing the asset or liability. In addition, the fair value for certain pension trust investments is determined using Net Asset Value per share (NAV) as a practical expedient, and therefore they are not classified within the fair value hierarchy. These investments primarily consist of institutional investment products. When developing fair value measurements, it is our policy to use quoted ma

Earnings Per Share

Earnings Per Share	12 Months Ended
	Dec. 31, 2019
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Earnings Per Share [Text Block]	EARNINGS PER SHARE Basic earnings or loss per share are computed using NW Holdings' net income or loss and the weighted average number of common shares outstanding for each period presented. Diluted earnings per share are computed in the same manner, except using the weighted average number of common shares outstanding plus the effects of the assumed exercise of stock options and the payment of estimated stock awards from other stock-based compensation plans that are outstanding at the end of each period presented. Anti-dilutive stock awards are excluded from the calculation of diluted earnings or loss per common share. NW Holdings' diluted earnings or loss per share are calculated as follows: In thousands, except per share data 2019 2018 2017 Net income from continuing operations $ 65,311 $ 67,311 $ 72,073 Loss from discontinued operations, net of tax (3,576 ) (2,742 ) (127,696 ) Net income (loss) $ 61,735 $ 64,569 $ (55,623 ) Average common shares outstanding - basic 29,786 28,803 28,669 Additional shares for stock-based compensation plans (See Note 8) 73 70 84 Average common shares outstanding - diluted 29,859 28,873 28,753 Earnings from continuing operations per share of common stock: Basic $ 2.19 $ 2.34 $ 2.51 Diluted 2.19 2.33 2.51 Loss from discontinued operations per share of common stock: Basic $ (0.12 ) $ (0.10 ) $ (4.45 ) Diluted (0.12 ) (0.09 ) (4.44 ) Earnings (loss) per share of common stock: Basic $ 2.07 $ 2.24 $ (1.94 ) Diluted 2.07 2.24 (1.93 ) Additional information: Anti-dilutive shares — 2 13

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2019
Segment Reporting [Abstract]
Segment Information	SEGMENT INFORMATION We primarily operate in one reportable business segment, which is NW Natural's local gas distribution business and is referred to as the NGD segment. During the second quarter of 2018, we moved forward with long-term strategic plans, which include a shift away from the California gas storage business, by entering into a Purchase and Sale Agreement that provides for the sale of all of the membership interests in Gill Ranch. As such, we reevaluated reportable segments and concluded that the remaining gas storage activities no longer meet the requirements of a reportable segment. Interstate Storage Services and asset management activities at the Mist gas storage facility are now reported as other under NW Natural. NW Natural and NW Holdings also have investments and business activities not specifically related to the NGD segment, which are aggregated and reported as other and described below for each entity. No individual customer accounts for over 10% of NW Holdings' or NW Natural's operating revenues. Natural Gas Distribution NW Natural's local gas distribution segment (NGD) is a regulated utility principally engaged in the purchase, sale, and delivery of natural gas and related services to customers in Oregon and southwest Washington. The NGD business is responsible for building and maintaining a safe and reliable pipeline distribution system, purchasing sufficient gas supplies from producers and marketers, contracting for firm and interruptible transportation of gas over interstate pipelines to bring gas from the supply basins into its service territory, and re-selling the gas to customers subject to rates, terms, and conditions approved by the OPUC or WUTC. NGD also includes taking customer-owned gas and transporting it from interstate pipeline connections, or city gates, to the customers’ end-use facilities for a fee, which is approved by the OPUC or WUTC. Approximately 89 % of NGD customers are located in Oregon and 11 % in Washington. On an annual basis, residential and commercial customers typically account for around 60% of total NGD volumes delivered and around 90% of NGD margin. Industrial customers largely account for the remaining volumes and NGD margin. A small amount of the margin is also derived from miscellaneous services, gains or losses from an incentive gas cost sharing mechanism, and other service fees. Industrial sectors served by the NGD business include: pulp, paper, and other forest products; the manufacture of electronic, electrochemical and electrometallurgical products; the processing of farm and food products; the production of various mineral products; metal fabrication and casting; the production of machine tools, machinery, and textiles; the manufacture of asphalt, concrete, and rubber; printing and publishing; nurseries; and government and educational institutions. In addition to NW Natural's local gas distribution business, the NGD segment also includes the portion of the Mist underground storage facility used to serve NGD customers, the North Mist gas storage expansion in Oregon, and NWN Gas Reserves, which is a wholly-owned subsidiary of Energy Corp. NW Natural NW Natural's activities in Other include Interstate Storage Services and third-party asset management services for the Mist facility in Oregon, appliance retail center operations, and corporate operating and non-operating revenues and expenses that cannot be allocated to NGD operations. Earnings from Interstate Storage Services assets are primarily related to firm storage capacity revenues. Earnings from the Mist facility also include revenue, net of amounts shared with NGD customers, from management of NGD assets at Mist and upstream pipeline capacity when not needed to serve NGD customers. Under the Oregon sharing mechanism, NW Natural retains 80 % of the pre-tax income from these services when the costs of the capacity were not included in NGD rates, or 10 % of the pre-tax income when the costs have been included in these rates. The remaining 20 % and 90 %, respectively, are recorded to a deferred regulatory account for crediting back to NGD customers. NW Holdings NW Holdings' activities in Other include all remaining activities not associated with NW Natural, specifically NWN Water, which consolidates the water and wastewater utility operations and is pursuing other investments in the water sector through itself and wholly-owned subsidiaries; NWN Gas Storage, a wholly-owned subsidiary of NWN Energy; NWN Energy's equity investment in TWH, which is pursuing development of a cross-Cascades transmission pipeline project (TWP); and other pipeline assets in NNG Financial. For more information on TWP, see Note 14 . Other also includes corporate revenues and expenses that cannot be allocated to other operations, including certain business development activities. All prior period amounts have been retrospectively adjusted to reflect the change in reportable segments and the designation of Gill Ranch as a discontinued operation for NW Holdings, and the designation of subsidiaries previously owned by NW Natural that are now owned by NW Holdings as discontinued operations for NW Natural. Segment Information Summary Inter-segment transactions were immaterial for the periods presented. The following table presents summary financial information concerning the reportable segment and other for continuing operations. See Note 19 for information regarding discontinued operations for NW Holdings and NW Natural. In thousands NGD Other NW Natural Other NW Holdings 2019 Operating revenues $ 720,528 $ 19,416 $ 739,944 $ 6,428 $ 746,372 Depreciation and amortization 89,415 990 90,405 1,091 91,496 Income (loss) from operations 135,918 11,428 147,346 (3,872 ) 143,474 Net income (loss) from continuing operations 60,828 8,146 68,974 (3,663 ) 65,311 Capital expenditures 219,880 1,500 221,380 2,091 223,471 Total assets at December 31, 2019 (1) 3,273,835 47,652 3,321,487 91,833 3,413,320 2018 Operating revenues $ 680,648 $ 24,923 $ 705,571 $ 572 $ 706,143 Depreciation and amortization 83,732 1,254 84,986 170 85,156 Income (loss) from operations 118,095 15,004 133,099 (937 ) 132,162 Net income (loss) from continuing operations 57,491 10,558 68,049 (738 ) 67,311 Capital expenditures 212,323 2,005 214,328 308 214,636 Total assets at December 31, 2018 (1) 3,141,969 50,767 3,192,736 36,657 3,229,393 2017 Operating revenues $ 732,942 $ 22,096 $ 755,038 $ — $ 755,038 Depreciation and amortization 79,734 1,290 81,024 29 81,053 Income (loss) from operations (2) 138,450 12,472 150,922 (20 ) 150,902 Net income from continuing operations 60,509 11,211 71,720 353 72,073 Capital expenditures 211,672 1,653 213,325 — 213,325 Total assets at December 31, 2017 (1) 2,961,326 50,471 3,011,797 14,075 3,025,872 (1) Total assets for NW Holdings exclude assets related to discontinued operations of $15.1 million , $13.3 million and $13.9 million as of December 31, 2019 , 2018 , and 2017 , respectively. Total assets for NW Natural exclude assets related to discontinued operations of $31.9 million as of December 31, 2017. (2) Includes $1.0 million of tax expense in NGD, $4.0 million of tax benefit in Other (NW Natural), and $0.4 million of tax benefit in Other (NW Holdings) from the TCJA remeasurement for the year ended December 31, 2017. Natural Gas Distribution Margin NGD margin is a financial measure used by the CODM, consisting of NGD operating revenues, reduced by the associated cost of gas, environmental remediation expense, and revenue taxes. The cost of gas purchased for NGD customers is generally a pass-through cost in the amount of revenues billed to regulated NGD customers. Environmental remediation expense represents collections received from customers through environmental recovery mechanisms in Oregon and Washington as well as adjustments for the Oregon environmental earnings test when applicable. This is offset by environmental remediation expense presented in operating expenses. Revenue taxes are collected from NGD customers and remitted to taxing authorities. The collections from customers are offset by the expense recognition of the obligation to the taxing authority. By subtracting cost of gas, environmental remediation expense, and revenue taxes from NGD operating revenues, NGD margin provides a key metric used by the CODM in assessing the performance of the NGD segment. The following table presents additional segment information concerning NGD margin: In thousands 2019 2018 2017 NGD margin calculation: NGD operating revenues $ 720,528 $ 680,648 $ 732,942 Less: NGD cost of gas 255,135 255,743 325,019 Environmental remediation expense 12,337 11,127 15,291 Revenue taxes (1) 30,325 30,082 — NGD margin $ 422,731 $ 383,696 $ 392,632 (1) The change in presentation of revenue taxes was a result of the adoption of ASU 2014-09 "Revenue From Contracts with Customers" and all related amendments on January 1, 2018. This change had no impact on NGD margin results as revenue taxes were previously presented net in NGD operating revenue. For additional information, see Note 2 .

Common Stock Common Stock

Common Stock Common Stock	12 Months Ended
	Dec. 31, 2019
Common Stock [Abstract]
Common Stock	COMMON STOCK As of December 31, 2019 and 2018 , NW Holdings had 100 million shares of common stock authorized. As of December 31, 2019 , NW Holdings had 206,560 shares reserved for issuance of common stock under the Employee Stock Purchase Plan (ESPP) and 340,133 shares reserved for issuance under the Dividend Reinvestment and Direct Stock Purchase Plan (DRPP). At NW Holdings' election, shares sold through the DRPP may be purchased in the open market or through original issuance of shares reserved for issuance under the DRPP. The Restated Stock Option Plan (SOP) was terminated with respect to new grants in 2012; however, options granted before the Restated SOP was terminated remain outstanding until the earlier of their expiration, forfeiture, or exercise. Options are now exercisable for shares of NW Holdings common stock. There were 10,938 options outstanding at December 31, 2019 , which were granted prior to termination of the plan. On June 7, 2019, NW Holdings completed the issuance of 1,437,500 shares of common stock, inclusive of the overallotment option granted to the underwriters, which was exercised in full. All shares were issued on June 7, 2019 at an offering price of $67.00 per share. The issuance resulted in proceeds to NW Holdings of $93.0 million , net of discounts and expenses. The issuance was executed to raise funds for general corporate purposes, including for equity contributions to NW Holdings’ subsidiaries, that are reflected as equity transfers on occurrence. Contributions received by NW Natural were also used, in part, to repay short-term indebtedness. Stock Repurchase Program NW Holdings has a share repurchase program under which it may purchase its common shares on the open market or through privately negotiated transactions. NW Holdings currently has Board authorization through May 2022 to repurchase up to an aggregate of the greater of 2.8 million shares or $100 million . No shares of common stock were repurchased pursuant to this program during the year ended December 31, 2019 . Since the plan’s inception in 2000 under NW Natural, a total of 2.1 million shares have been repurchased at a total cost of $83.3 million . The following table summarizes the changes in the number of shares of NW Holdings' common stock issued and outstanding: In thousands Shares Balance, December 31, 2016 28,630 Sales to employees under ESPP 18 Stock-based compensation 88 Balance, December 31, 2017 28,736 Sales to employees under ESPP 19 Stock-based compensation 64 Sales to shareholders under DRPP 61 Balance, December 31, 2018 28,880 Sales to employees under ESPP 18 Stock-based compensation 83 Equity Issuance 1,438 Sales to shareholders under DRPP 53 Balance, December 31, 2019 30,472

Revenue Revenue

Revenue Revenue	12 Months Ended
	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Revenue	REVENUE The following table presents disaggregated revenue from continuing operations: Year ended December 31, 2019 In thousands NGD Other (NW Natural) NW Natural Other (NW Holdings) NW Holdings Natural gas sales $ 729,296 $ — $ 729,296 $ — $ 729,296 Gas storage revenue, net — 10,240 10,240 — 10,240 Asset management revenue, net — 3,705 3,705 — 3,705 Appliance retail center revenue — 5,471 5,471 — 5,471 Other revenue 847 — 847 6,428 7,275 Revenue from contracts with customers 730,143 19,416 749,559 6,428 755,987 Alternative revenue (20,984 ) — (20,984 ) — (20,984 ) Leasing revenue 11,369 — 11,369 — 11,369 Total operating revenues $ 720,528 $ 19,416 $ 739,944 $ 6,428 $ 746,372 Year ended December 31, 2018 In thousands NGD Other (NW Natural) NW Natural Other (NW Holdings) NW Holdings Natural gas sales $ 670,662 $ — $ 670,662 $ — $ 670,662 Gas storage revenue, net — 10,780 10,780 — 10,780 Asset management revenue, net — 8,548 8,548 — 8,548 Appliance retail center revenue — 5,595 5,595 — 5,595 Other revenue — — — 572 572 Revenue from contracts with customers 670,662 24,923 695,585 572 696,157 Alternative revenue 8,989 — 8,989 — 8,989 Leasing revenue 997 — 997 — 997 Total operating revenues $ 680,648 $ 24,923 $ 705,571 $ 572 $ 706,143 NW Natural's revenue represents substantially all of NW Holdings' revenue and is recognized for both registrants when the obligation to customers is satisfied and in the amount expected to be received in exchange for transferring goods or providing services. Revenue from contracts with customers contains one performance obligation that is generally satisfied over time, using the output method based on time elapsed, due to the continuous nature of the service provided. The transaction price is determined by a set price agreed upon in the contract or dependent on regulatory tariffs. Customer accounts are settled on a monthly basis or paid at time of sale and based on historical experience. It is probable that we will collect substantially all of the consideration to which we are entitled. NW Holdings and NW Natural do not have any material contract assets, as net accounts receivable and accrued unbilled revenue balances are unconditional and only involve the passage of time until such balances are billed and collected. NW Holdings and NW Natural do not have any material contract liabilities. Revenue-based taxes are primarily franchise taxes, which are collected from NGD customers and remitted to taxing authorities. Beginning January 1, 2018, revenue taxes are included in operating revenues with an equal and offsetting expense recognized in operating expenses in the consolidated statements of comprehensive income. Natural Gas Distribution Natural gas sales. NW Natural's primary source of revenue is providing natural gas to customers in the NGD service territory, which includes residential, commercial, industrial and transportation customers. NGD revenue is generally recognized over time upon delivery of the gas commodity or service to the customer, and the amount of consideration received and recognized as revenue is dependent on the Oregon and Washington tariffs. Customer accounts are to be paid in full each month, and there is no right of return or warranty for services provided. Revenues include firm and interruptible sales and transportation services, franchise taxes recovered from the customer, late payment fees, service fees, and accruals for gas delivered but not yet billed (accrued unbilled revenue). The accrued unbilled revenue balance is based on estimates of deliveries during the period from the last meter reading and management judgment is required for a number of factors used in this calculation, including customer use and weather factors. We applied the significant financing practical expedient and have not adjusted the consideration NW Natural expects to receive from NGD customers for the effects of a significant financing component as all payment arrangements are settled annually. Due to the election of the right to invoice practical expedient, we do not disclose the value of unsatisfied performance obligations as of December 31, 2019 . Alternative revenue. Weather normalization (WARM) and decoupling mechanisms are considered to be alternative revenue programs. Alternative revenue programs are considered to be contracts between NW Natural and its regulator and are excluded from revenue from contracts with customers. Leasing revenue. Leasing revenue primarily consists of revenues from NW Natural's North Mist Storage contract with Portland General Electric (PGE) in support of PGE's gas-fired electric power generation facilities under an initial 30 -year contract with options to extend, totaling up to an additional 50 years upon mutual agreement of the parties. The facility is accounted for as a sales-type lease with regulatory accounting deferral treatment. The investment is included in rate base under an established cost-of-service tariff schedule, with revenues recognized according to the tariff schedule and as such, profit upon commencement was deferred and will be amortized over the lease term. Leasing revenue also contains rental revenue from small leases of property owned by NW Natural to third parties. The majority of these transactions are accounted for as operating leases and the revenue is recognized over the term of the lease agreement. Lease revenue is excluded from revenue from contracts with customers. See Note 7. NW Natural Other Gas storage revenue. NW Natural's other revenue includes gas storage activity, which includes Mist Interstate Storage Services used to store natural gas for customers. Gas storage revenue is generally recognized over time as the gas storage service is provided to the customer and the amount of consideration received and recognized as revenue is dependent on set rates defined per the storage agreements. Noncash consideration in the form of dekatherms of natural gas is received as consideration for providing gas injection services to gas storage customers. This noncash consideration is measured at fair value using the average spot rate. Customer accounts are generally paid in full each month, and there is no right of return or warranty for services provided. Revenues include firm and interruptible storage services, net of the regulatory sharing amount refunded to NGD customers. Asset management revenue. Revenues include the optimization of the storage assets and pipeline capacity and are provided net of the profit sharing amount refunded to NGD customers. Certain asset management revenues received are recognized over time using a straight-line approach over the term of each contract, and the amount of consideration received and recognized as revenue is dependent on a variable pricing model. Variable revenues earned above guaranteed amounts are estimated and recognized at the end of each period using the most likely amount approach. Additionally, other asset management revenues may be based on a fixed rate. Generally, asset management accounts are settled on a monthly basis. As of December 31, 2019 , unrecognized revenue for the fixed component of the transaction price related to gas storage and asset management revenue was approximately $73.4 million . Of this amount, approximately $16.0 million will be recognized in 2020 , $18.2 million in 2021 , $14.5 million in 2022 , $11.6 million in 2023 , $7.8 million in 2024 , and $5.3 million thereafter. The amounts presented here are calculated using current contracted rates. Appliance retail center revenue. NW Natural owns and operates an appliance store that is open to the public, where customers can purchase natural gas home appliances. Revenue from the sale of appliances is recognized at the point in time in which the appliance is transferred to the third party responsible for delivery and installation services and when the customer has legal title to the appliance. It is required that the sale be paid for in full prior to transfer of legal title. The amount of consideration received and recognized as revenue varies with changes in marketing incentives and discounts offered to customers. NW Holdings Other NW Holdings' primary source of other revenue is providing water and wastewater services to customers. Water distribution and wastewater collection revenue is generally recognized over time upon delivery of the water commodity or wastewater collection service to the customer, and the amount of consideration received and recognized as revenue is dependent on the water customer rates set by the applicable state public utility commission and contractual rates for wastewater customers. Customer accounts are to be paid in full each month, and there is no right of return or warranty for services provided. We applied the significant financing practical expedient and have not adjusted the consideration we expect to receive from water distribution and wastewater collection customers for the effects of a significant financing component as all payment arrangements are settled annually. Due to the election of the right to invoice practical expedient, we do not disclose the value of unsatisfied performance obligations as of December 31, 2019 .

Leases (Notes)

Leases (Notes)	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Leases of Lessee Disclosure	LEASES Lease Revenue Leasing revenue primarily consists of NW Natural's North Mist natural gas storage agreement with PGE which is billed under an OPUC-approved rate schedule and includes an initial 30 -year term with options to extend, totaling up to an additional 50 years upon mutual agreement of the parties. Under U.S. GAAP, this agreement is classified as a sales-type lease and qualifies for regulatory accounting deferral treatment. The investment in the storage facility is included in rate base under a separately established cost-of-service tariff, with revenues recognized according to the tariff schedule. As such, the selling profit that was calculated upon commencement as part of the sale-type lease recognition was deferred and will be amortized over the lease term. Billing rates under the cost-of-service tariff will be updated annually to reflect current information including depreciable asset levels, forecasted operating expenses, and the results of regulatory proceedings, as applicable, and revenue received under this agreement is recognized as operating revenue on the consolidated statements of comprehensive income. There are no variable payments or residual value guarantees. The lease does not contain an option to purchase the underlying assets. NW Natural also maintains a sales-type lease for specialized compressor facilities to provide high pressure compressed natural gas (CNG) services. Lease payments are outlined in an OPUC-approved rate schedule over a 10 -year term. There are no variable payments or residual value guarantees. The selling profit computed upon lease commencement was not significant. Our lessor portfolio also contains small leases of property owned by NW Natural to third parties. These transactions are accounted for as operating leases and the revenue is recognized over the term of the lease agreement. The components of lease revenue at NW Natural were as follows: In thousands Year ended December 31, 2019 Lease revenue Operating leases $ 171 Sales-type leases 11,198 Total lease revenue $ 11,369 Total future minimum lease payments to be received under non-cancelable leases at NW Natural at December 31, 2019 are as follows: In thousands Operating Sales-Type Total 2020 $ 65 $ 18,228 $ 18,293 2021 49 17,518 17,567 2022 45 17,026 17,071 2023 45 16,557 16,602 2024 45 15,867 15,912 Thereafter 93 264,740 264,833 Total lease revenue $ 342 $ 349,936 $ 350,278 Less: imputed interest 202,319 Total leases receivable $ 147,617 The total leases receivable above is reported under the NGD segment and the short- and long-term portions are included within other current assets and assets under sales-type leases on the consolidated balance sheets, respectively. The total amount of unguaranteed residual assets at December 31, 2019 was $4.0 million and is included in assets under sales-type leases on the consolidated balance sheets. Additionally, under regulatory accounting, the revenues and expenses associated with these agreements are presented on the consolidated statements of comprehensive income such that their presentation aligns with similar regulated activities at NW Natural. Additionally, future minimum lease payments of $0.5 million for each of the years ending 2020, 2021 and 2022 are to be received under non-cancelable operating leases associated with non-utility property rentals. For the year ended December 31, 2019 , approximately $0.5 million of lease revenue is presented in other income (expense), net on the consolidated statements of comprehensive income as it is non-operating income. Lease Expense Operating Leases We have operating leases for land, buildings and equipment. Our primary lease is for NW Natural's operations center. Our leases have remaining lease terms of one year to 11 years. Many of our lease agreements include options to extend the lease, which we do not include in our minimum lease terms unless they are reasonably certain to be exercised. Short-term leases with a term of 12 months or less are not recorded on the balance sheet. As most of our leases do not provide an implicit rate and are entered into by NW Natural, we use NW Natural's incremental borrowing rate based on information available at the lease commencement date in determining the present value of lease payments. The components of lease expense, a portion of which is capitalized, were as follows: Year ended December 31, 2019 In thousands NW Natural Other NW Holdings Operating lease expense $ 4,620 $ 191 $ 4,811 Short-term lease expense 1,146 — 1,146 Supplemental balance sheet information related to operating leases as of December 31, 2019 is as follows: In thousands NW Natural Other NW Holdings Operating lease right of use assets $ 2,760 $ 190 $ 2,950 Operating lease liabilities - current liabilities $ 1,979 $ 122 $ 2,101 Operating lease liabilities - non-current liabilities 772 69 841 Total operating lease liabilities $ 2,751 $ 191 $ 2,942 As of December 31, 2019 , the weighted average remaining lease term for the operating leases is one year for NW Natural. The weighted average discount rate used in the valuation of the operating lease right of use assets over the remaining lease term is 3.98% for NW Natural. Maturities of operating lease liabilities at December 31, 2019 were as follows: In thousands NW Natural Other NW Holdings 2020 $ 2,029 $ 126 $ 2,155 2021 143 52 195 2022 111 18 129 2023 88 — 88 2024 89 — 89 Thereafter 526 — 526 Total lease payments 2,986 196 3,182 Less: imputed interest 235 5 240 Total lease obligations 2,751 191 2,942 Less: current obligations 1,979 122 2,101 Long-term lease obligations $ 772 $ 69 $ 841 As of December 31, 2019 , finance lease liabilities with maturities of less than one year were $0.2 million at NW Natural. Significant Lease Not Yet Commenced In October 2017, NW Natural entered into a 20 -year operating lease agreement for a new corporate operations center in Portland, Oregon in anticipation of the expiration of the current operations center lease in 2020. The lease commenced in the first quarter of 2020 and total estimated base rent payments over the life of the lease are approximately $160 million . There is an option to extend the term of the lease for two additional periods of seven years . Cash Flow Information Supplemental cash flow information related to leases was as follows: Year ended December 31, 2019 NW Natural Other NW Holdings Cash paid for amounts included in the measurement of lease liabilities Operating cash flows from operating leases $ 4,447 $ 182 $ 4,629 Finance cash flows from finance leases 120 — 120 Right of use assets obtained in exchange for lease obligations Operating leases $ 7,205 $ 372 $ 7,577 Finance leases 312 — 312 Finance Leases NW Natural also leases building storage spaces for use as a gas meter room in order to provide natural gas to multifamily or mixed use developments. These contracts are accounted for as finance leases and typically involve a one-time upfront payment with no remaining liability. The right of use asset for finance leases was $0.5 million at December 31, 2019 . Lease Disclosures Related to Periods Prior to the First Quarter of 2019 Land, buildings, and equipment are leased under agreements that expire in various years, including a 99-year land lease that extends through 2108. Rental costs for continuing operations were $5.9 million , $7.3 million , and $5.9 million for the years ended December 31, 2018, 2017, and 2016, respectively, a portion of which was capitalized. The following table reflects NW Natural's future minimum lease payments due under non-cancelable operating leases for continuing operations at December 31, 2018. These commitments relate principally to the lease of the corporate operations center and underground gas storage facilities. In thousands Minimum lease payments 2019 $ 5,368 2020 4,812 2021 7,077 2022 7,223 2023 7,304 Thereafter 149,881 Total $ 181,665

Debt

Debt	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Debt [Text Block]	DEBT Short-Term Debt The primary source of short-term liquidity for NW Holdings is cash balances, dividends from its operating subsidiaries, in particular NW Natural, available cash from a multi-year credit facility, and short-term credit facilities it may enter into from time to time. The primary source of short-term liquidity for NW Natural is from the sale of commercial paper, its multi-year credit facilities, and short-term credit facilities it may enter into from time to time. In addition to issuing commercial paper or bank loans to meet working capital requirements, including seasonal requirements to finance gas purchases and accounts receivable, short-term debt may also be used to temporarily fund capital requirements. For NW Natural, commercial paper and bank loans are periodically refinanced through the sale of long-term debt or equity contributions from NW Holdings. NW Natural's commercial paper is sold through two commercial banks under an issuing and paying agency agreement and is supported by one or more unsecured revolving credit facilities. See “ Credit Agreements ” below. At December 31, 2019 and 2018 , NW Holdings had short-term debt outstanding of $149.1 million and $217.6 million , respectively. The weighted average interest rate of NW Holdings' short-term debt outstanding at December 31, 2019 and 2018 was 2.0% and 3.0% , respectively. At December 31, 2019 and 2018 , NW Natural had $125.1 million and $217.5 million of commercial paper outstanding, respectively. The weighted average interest rate of commercial paper outstanding at December 31, 2019 and 2018 was 2.0% and 3.0% , respectively. The carrying cost of commercial paper approximates fair value using Level 2 inputs. See Note 2 for a description of the fair value hierarchy. At December 31, 2019 , NW Natural's commercial paper had a maximum remaining maturity of 22 days and an average remaining maturity of 10 days. Credit Agreements NW Holdings In October 2018, NW Holdings entered into a $100.0 million credit agreement, with a feature that allows it to request increases in the total commitment amount, up to a maximum of $150.0 million . The maturity date of the agreement is October 2, 2023 , with available extensions of commitments for two additional one-year periods, subject to lender approval. The NW Holdings credit agreement permits the issuance of letters of credit in an aggregate amount of up to $40.0 million . The principal amount of borrowings under the credit agreement is due and payable on the maturity date. The credit agreement requires NW Holdings to maintain a consolidated indebtedness to total capitalization ratio of 70% or less. Failure to comply with this covenant would entitle the lenders to terminate their lending commitments and accelerate the maturity of all amounts outstanding. NW Holdings was in compliance with this covenant at December 31, 2019 and 2018 . The agreement also requires NW Holdings to maintain debt ratings (which are defined by a formula using NW Natural's credit ratings in the event NW Holdings does not have a credit rating) with Standard & Poor's (S&P) and Moody's Investors Service, Inc. (Moody’s) and notify the lenders of any change in its senior unsecured debt ratings or senior secured debt ratings, as applicable, by such rating agencies. A change in NW Holdings' debt ratings by S&P or Moody’s is not an event of default, nor is the maintenance of a specific minimum level of debt rating a condition of drawing upon the credit agreement. Rather, interest rates on any loans outstanding under the credit agreements are tied to debt ratings and therefore, a change in the debt rating would increase or decrease the cost of any loans under the credit agreements when ratings are changed. NW Holdings does not currently maintain ratings with S&P or Moody's. There was a $24.0 million outstanding balance and no outstanding balances under the NW Holdings agreement at December 31, 2019 and 2018 , respectively. No letters of credit were issued or outstanding under the NW Holdings agreement at December 31, 2019 and 2018 . NW Holdings had $1.0 million and $2.8 million of letters of credit issued and outstanding in support of acquisitions of water companies, separate from the aforementioned credit agreement, at December 31, 2019 and 2018 , respectively. NW Natural In October 2018, NW Natural entered into a new multi-year credit agreement for unsecured revolving loans totaling $300.0 million , with a feature that allows NW Natural to request increases in the total commitment amount, up to a maximum of $450.0 million . The maturity date of the agreement is October 2, 2023 with available extensions of commitments for two additional one-year periods, subject to lender approval. The new credit agreement is substantially similar to the prior credit agreement which was terminated upon the closing of the New Credit Agreement. The new credit agreement permits the issuance of letters of credit in an aggregate amount of up to $60.0 million . The principal amount of borrowings under the credit agreement is due and payable on the maturity date. There were no outstanding balances under NW Natural's prior credit agreement or the new credit agreement and no letters of credit issued or outstanding at December 31, 2019 and 2018 . NW Natural's prior credit agreement and the new credit agreement require NW Natural to maintain a consolidated indebtedness to total capitalization ratio of 70% or less. Failure to comply with this covenant would entitle the lenders to terminate their lending commitments and accelerate the maturity of all amounts outstanding. NW Natural was in compliance with this covenant at December 31, 2019 and 2018 . The new credit agreement also requires NW Natural to maintain credit ratings with S&P and Moody’s and notify the lenders of any change in NW Natural's senior unsecured debt ratings or senior secured debt ratings, as applicable, by such rating agencies. A change in NW Natural's debt ratings by S&P or Moody’s is not an event of default, nor is the maintenance of a specific minimum level of debt rating a condition of drawing upon the new credit agreement. Rather, interest rates on any loans outstanding under the new credit agreement are tied to debt ratings and therefore, a change in the debt rating would increase or decrease the cost of any loans under the new credit agreement when ratings are changed. Long-Term Debt NW Holdings At December 31, 2019 and 2018 , NW Holdings had long-term debt outstanding of $881.1 million and $736.2 million , respectively; which included $5.7 million and $5.6 million of unamortized debt issuance costs at NW Natural, respectively. NW Holdings' long-term debt is primarily comprised of debt held at its wholly-owned subsidiaries NW Natural (shown below) and NWN Water. Long-term debt at NWN Water is primarily comprised of a two-year term loan agreement for $35.0 million , due in 2021 . NWN Water entered into this agreement in June 2019 and the loan carried an interest rate of 2.35% at December 31, 2019 , which is based upon the one-month LIBOR rate. The loan is guaranteed by NW Holdings and requires NW Holdings to maintain a consolidated indebtedness to total capitalization ratio of 70% or less. Failure to comply with this covenant would entitle the lenders to terminate their lending commitments and accelerate the maturity of all amounts outstanding. NW Holdings was in compliance with this covenant at December 31, 2019 , with a consolidated indebtedness to total capitalization ratio of 54.3% . NW Natural NW Natural's issuance of FMBs, which includes NW Natural's medium-term notes, under the Mortgage and Deed of Trust (Mortgage) is limited by eligible property, adjusted net earnings, and other provisions of the Mortgage. The Mortgage constitutes a first mortgage lien on substantially all of NW Natural's NGD property. Maturities and Outstanding Long-Term Debt Retirement of long-term debt for each of the annual periods through December 31, 2024 and thereafter are as follows: In thousands Long-term debt maturities 2020 $ 75,000 2021 60,000 2022 — 2023 90,000 2024 — Thereafter 624,700 The following table presents debt outstanding as of December 31: In thousands 2019 2018 NW Natural First Mortgage Bonds: 8.310% Series due 2019 $ — $ 10,000 7.630% Series due 2019 — 20,000 5.370% Series due 2020 75,000 75,000 9.050% Series due 2021 10,000 10,000 3.176% Series due 2021 50,000 50,000 3.542% Series due 2023 50,000 50,000 5.620% Series due 2023 40,000 40,000 7.720% Series due 2025 20,000 20,000 6.520% Series due 2025 10,000 10,000 7.050% Series due 2026 20,000 20,000 3.211% Series due 2026 35,000 35,000 7.000% Series due 2027 20,000 20,000 2.822% Series due 2027 25,000 25,000 6.650% Series due 2027 19,700 19,700 6.650% Series due 2028 10,000 10,000 3.141% Series due 2029 50,000 — 7.740% Series due 2030 20,000 20,000 7.850% Series due 2030 10,000 10,000 5.820% Series due 2032 30,000 30,000 5.660% Series due 2033 40,000 40,000 5.250% Series due 2035 10,000 10,000 4.000% Series due 2042 50,000 50,000 4.136% Series due 2046 40,000 40,000 3.685% Series due 2047 75,000 75,000 4.110% Series due 2048 50,000 50,000 3.869% Series due 2049 90,000 — Long-term debt, gross 849,700 739,700 Less: current maturities 75,000 30,000 Total long-term debt $ 774,700 $ 709,700 First Mortgage Bonds In June 2019 , NW Natural issued $140.0 million of FMBs consisting of $50.0 million with an interest rate of 3.141% , due in 2029 , and $90.0 million with an interest rate of 3.869% , due in 2049 . In September 2018 , NW Natural issued $50.0 million of FMBs with an interest rate of 4.110% , due in 2048 . Retirements of Long-Term Debt In September 2019 , NW Natural retired $10.0 million of FMBs with an interest rate of 8.310% , and retired $20.0 million of FMBs with an interest rate of 7.630% in December 2019 . In March 2018 , NW Natural retired $22.0 million of FMBs with an interest rate of 6.600% , and retired $75.0 million of FMBs with an interest rate of 1.545% in December 2018 . Fair Value of Long-Term Debt NW Holdings' and NW Natural's outstanding debt does not trade in active markets. The fair value of debt is estimated using natural gas distribution companies with similar credit ratings, terms, and remaining maturities to NW Holdings' and NW Natural's debt that actively trade in public markets. Substantially all outstanding debt at NW Holdings is comprised of NW Natural debt. These valuations are based on Level 2 inputs as defined in the fair value hierarchy. See Note 2 . The following table provides an estimate of the fair value of NW Holdings' long-term debt, including current maturities of long-term debt, using market prices in effect on the valuation date : December 31, In thousands 2019 2018 Gross long-term debt $ 886,776 $ 741,813 Unamortized debt issuance costs (5,712 ) (5,577 ) Carrying amount $ 881,064 $ 736,236 Estimated fair value $ 957,268 $ 762,335 The following table provides an estimate of the fair value of NW Natural's long-term debt, including current maturities of long-term debt, using market prices in effect on the valuation date : December 31, In thousands 2019 2018 Gross long-term debt $ 849,700 $ 739,700 Unamortized debt issuance costs (5,712 ) (5,577 ) Carrying amount $ 843,988 $ 734,123 Estimated fair value $ 919,835 $ 760,222

Stock-Based Compensation (Notes

Stock-Based Compensation (Notes)	12 Months Ended
	Dec. 31, 2019
Share-based Payment Arrangement [Abstract]
Share-based Payment Arrangement [Text Block]	STOCK-BASED COMPENSATION Stock-based compensation plans are designed to promote stock ownership in NW Holdings by employees and officers of NW Holdings and its affiliates. These compensation plans include a Long Term Incentive Plan (LTIP), an ESPP, and a Restated SOP. Long Term Incentive Plan The LTIP is intended to provide a flexible, competitive compensation program for eligible officers and key employees. Under the LTIP, shares of NW Holdings common stock are authorized for equity incentive grants in the form of stock, restricted stock, restricted stock units, stock options, or performance shares. An aggregate of 1,100,000 shares were authorized for issuance as of December 31, 2019 . Shares awarded under the LTIP may be purchased on the open market or issued as original shares. Of the 1,100,000 shares of common stock authorized for LTIP awards at December 31, 2019 , there were 510,931 shares available for issuance under any type of award. This assumes market, performance, and service-based grants currently outstanding are awarded at the target level. There were no outstanding grants of restricted stock or stock options under the LTIP at December 31, 2019 or 2018 . The LTIP stock awards are compensatory awards for which compensation expense is based on the fair value of stock awards, with expense being recognized over the performance and vesting period of the outstanding awards. Forfeitures are recognized as they occur. Performance Shares LTIP performance shares incorporate a combination of market, performance, and service-based factors. The following table summarizes performance share expense information: Dollars in thousands Shares (1) Expense During Award Year (2) Total Expense for Award Estimated award: 2017-2019 grant (3) 41,573 $ 572 $ 1,971 Actual award: 2016-2018 grant 28,218 598 1,413 2015-2017 grant 18,304 (346 ) 1,169 (1) In addition to common stock shares, a participant also receives a dividend equivalent cash payment equal to the number of shares of common stock received on the award payout multiplied by the aggregate cash dividends paid per share during the performance period. (2) Amount represents the expense recognized in the third year of the vesting period noted above. For the 2015-2017 grant, targets were not met and expense that had been previously recognized was reversed during 2017. (3) This represents the estimated number of shares to be awarded as of December 31, 2019 as certain performance share measures have been achieved. Amounts are subject to change with final payout amounts authorized by the Board of Directors in February 2020 . The aggregate number of performance shares granted and outstanding at the target and maximum levels were as follows: Dollars in thousands Performance Share Awards Outstanding 2019 Cumulative Expense Performance Period Target Maximum Expense December 31, 2019 2017-19 30,234 60,468 $ 572 $ 1,971 2018-20 — — — — 2019-21 — — — — Total 30,234 60,468 $ 572 For the 2017-2019 performance period, performance share awards are based on the achievement of EPS and Return on Invested Capital (ROIC) factors, which can be modified by a Total Shareholder Return (TSR) factor relative to the performance of the Russell 2500 Utilities Index over the three-year performance period and a growth modifier based on accumulative EBITDA. For the 2018-2020 and 2019-2021 performance period, performance share awards are based on the achievement of a three-year ROIC threshold that must be met and a cumulative EPS factor, which can be modified by a TSR factor relative to the performance of the Russell 2500 Utilities Index over the three-year performance period. The 2018-2020 and 2019-2021 performance period allows for one of the performance factors to remain variable until the first quarter of the third year of the award period. As the performance factor will not be approved until the first quarter of 2020 and 2021, there is not a mutual understanding of the awards' key terms and conditions between NW Natural and the participants as of December 31, 2019, and therefore, no expense was recognized for the 2018-2020 and 2019-2021 performance period. NW Natural will calculate the grant date fair value and recognize expense once the final performance factor has been approved. If the target is achieved for the 2018-2020 and 2019-2021 awards, NW Holdings would grant 31,825 and 35,170 shares in the first quarter of 2020 and 2021, respectively. Compensation expense is recognized in accordance with accounting standards for stock-based compensation and calculated based on performance levels achieved and an estimated fair value using the Monte-Carlo method. Due to there not being a mutual understanding of the 2018-2020 and 2019-2021 awards' key terms and conditions as noted above, the grant date fair value has not yet been determined and no nonvested shares existed at December 31, 2019 . The weighted-average grant date fair value of nonvested shares associated with the 2017-2019 awards was $ 57.05 per share at December 31, 2018 . The weighted-average grant date fair value of shares vested during the year was $ 57.05 per share and there were no performance shares granted during the year and no unrecognized compensation expense for accounting purposes as of December 31, 2019 . Restricted Stock Units In 2012, RSUs began being granted under the LTIP instead of stock options under the Restated SOP. Generally, the RSUs awarded are forfeitable and include a performance-based threshold as well as a vesting period of four years from the grant date. Upon vesting, the RSU holder is issued one share of common stock plus a cash payment equal to the total amount of dividends paid per share between the grant date and vesting date of that portion of the RSU. The fair value of an RSU is equal to the closing market price of NW Holdings' common stock on the grant date. During 2019 , total RSU expense was $ 1.8 million compared to $ 1.8 million in 2018 and $ 1.6 million in 2017 . As of December 31, 2019 , there was $ 3.4 million of unrecognized compensation cost from grants of RSUs, which is expected to be recognized over a period extending through 2024 . Information regarding the RSU activity is summarized as follows: Number of RSUs Weighted - Average Price Per RSU Nonvested, December 31, 2016 89,973 $ 48.85 Granted 32,168 60.51 Vested (35,341 ) 47.07 Forfeited (2,278 ) 53.78 Nonvested, December 31, 2017 84,522 53.90 Granted 32,450 57.59 Vested (32,689 ) 50.75 Forfeited (1,603 ) 59.95 Nonvested, December 31, 2018 82,680 56.47 Granted 36,018 65.29 Vested (35,778 ) 54.22 Forfeited (3,187 ) 63.89 Nonvested, December 31, 2019 79,733 $ 61.17 Restated Stock Option Plan The NW Natural Restated SOP was terminated for new option grants in 2012; however, options granted before the plan terminated remain outstanding until the earlier of their expiration, forfeiture, or exercise and are now exercisable for shares of NW Holdings common stock. Any new grants of stock options will be made under NW Holdings' LTIP, however, no option grants have been awarded since 2012 and all stock options were vested as of December 31, 2015. Options under the Restated SOP were granted to officers and key employees designated by a committee of the Board of Directors. All options were granted at an option price equal to the closing market price on the date of grant and may be exercised for a period of up to 10 years and seven days from the date of grant. Option holders may exchange shares they have owned for at least six months , valued at the current market price, to purchase shares at the option price. Information regarding the Restated SOP activity is summarized as follows: Option Shares Weighted - Average Price Per Share Intrinsic Value (In millions) Balance outstanding and exercisable, December 31, 2016 180,163 $ 44.38 $ 2.8 Exercised (88,275 ) 44.33 1.8 Forfeited (200 ) 41.15 n/a Balance outstanding and exercisable, December 31, 2017 91,688 44.43 1.4 Exercised (35,450 ) 43.61 0.8 Forfeited (300 ) 43.29 n/a Balance outstanding and exercisable, December 31, 2018 55,938 44.96 0.9 Exercised (45,000 ) 44.79 1.0 Expired — — n/a Balance outstanding and exercisable, December 31, 2019 10,938 $ 45.67 $ 0.3 During 2019 , cash of $ 2.0 million was received for stock options exercised and $ 0.2 million related tax benefit was recognized. The weighted-average remaining life of options exercisable and outstanding at December 31, 2019 was 1.12 years. Employee Stock Purchase Plan NW Holdings' ESPP allows employees of NW Holdings, NW Natural and certain designated subsidiaries to purchase common stock at 85% of the closing price on the trading day immediately preceding the initial offering date, which is set annually. For the 2019-2020 ESPP period, each eligible employee may purchase up to $ 21,222 worth of stock through payroll deductions over a period defined by the Board of Directors, with shares issued at the end of the subscription period. Stock-Based Compensation Expense Stock-based compensation expense is recognized as operations and maintenance expense or is capitalized as part of construction overhead at the entity at which the award recipient is employed. The following table summarizes the NW Holdings' financial statement impact, substantially all of which was recorded at NW Natural, of stock-based compensation under the LTIP, Restated SOP and ESPP: In thousands 2019 2018 2017 Operations and maintenance expense, for stock-based compensation $ 2,172 $ 2,489 $ 2,354 Income tax benefit (575 ) (659 ) (930 ) Net stock-based compensation effect on net income (loss) 1,597 1,830 1,424 Amounts capitalized for stock-based compensation $ 430 $ 531 $ 528

Pension and Other Postretiremen

Pension and Other Postretirement Benefits Costs	12 Months Ended
	Dec. 31, 2019
Retirement Benefits [Abstract]
Pension and Other Postretirement Benefits Costs	PENSION AND OTHER POSTRETIREMENT BENEFIT COSTS NW Natural maintains a qualified non-contributory defined benefit pension plan (Pension Plan), non-qualified supplemental pension plans for eligible executive officers and other key employees, and other postretirement employee benefit plans. NW Natural also has a qualified defined contribution plan (Retirement K Savings Plan) for all eligible employees. The Pension Plan and Retirement K Savings Plan have plan assets, which are held in qualified trusts to fund retirement benefits. Effective January 1, 2007 and 2010, the qualified defined benefit pension plans and postretirement benefits for non-union employees and union employees, respectively, were closed to new participants. Non-union and union employees hired or re-hired after December 31, 2006 and 2009, respectively, and employees of NW Natural subsidiaries are provided an enhanced Retirement K Savings Plan benefit. The following table provides a reconciliation of the changes in NW Natural's benefit obligations and fair value of plan assets, as applicable, for NW Natural's pension and other postretirement benefit plans, excluding the Retirement K Savings Plan, and a summary of the funded status and amounts recognized in NW Holdings' and NW Natural's consolidated balance sheets as of December 31: Postretirement Benefit Plans Pension Benefits Other Benefits In thousands 2019 2018 2019 2018 Reconciliation of change in benefit obligation: Obligation at January 1 $ 455,568 $ 486,289 $ 28,172 $ 28,927 Service cost 6,308 7,185 244 282 Interest cost 18,683 16,991 1,117 964 Net actuarial (gain) loss 58,269 (32,979 ) 1,809 (327 ) Benefits paid (23,160 ) (21,918 ) (1,774 ) (1,674 ) Obligation at December 31 $ 515,668 $ 455,568 $ 29,568 $ 28,172 Reconciliation of change in plan assets: Fair value of plan assets at January 1 $ 257,797 $ 287,925 $ — $ — Actual return on plan assets 65,104 (25,925 ) — — Employer contributions 13,310 17,715 1,774 1,674 Benefits paid (23,160 ) (21,918 ) (1,774 ) (1,674 ) Fair value of plan assets at December 31 $ 313,051 $ 257,797 $ — $ — Funded status at December 31 $ (202,617 ) $ (197,771 ) $ (29,568 ) $ (28,172 ) NW Natural's Pension Plan had a projected benefit obligation of $ 477.3 million and $ 420.2 million at December 31, 2019 and 2018 , respectively, and fair values of plan assets of $ 313.1 million and $ 257.8 million , respectively. The plan had an accumulated benefit obligation of $434.9 million and $385.9 million at December 31, 2019 and 2018 , respectively. The following table presents amounts realized through regulatory assets or in other comprehensive loss (income) for the years ended December 31: Regulatory Assets Other Comprehensive Loss (Income) Pension Benefits Other Postretirement Benefits Pension Benefits In thousands 2019 2018 2017 2019 2018 2017 2019 2018 2017 Net actuarial loss (gain) $ 10,424 $ 14,261 $ 12,177 $ 1,809 $ (327 ) $ (214 ) $ 3,595 $ (677 ) $ 2,777 Amortization of: Prior service cost (7 ) (42 ) (127 ) 468 468 468 — — — Actuarial loss (14,057 ) (18,761 ) (14,802 ) (369 ) (448 ) (696 ) (648 ) (1,052 ) (946 ) Total $ (3,640 ) $ (4,542 ) $ (2,752 ) $ 1,908 $ (307 ) $ (442 ) $ 2,947 $ (1,729 ) $ 1,831 The following table presents amounts recognized in regulatory assets and accumulated other comprehensive loss (AOCL) at December 31: Regulatory Assets AOCL Pension Benefits Other Postretirement Benefits Pension Benefits In thousands 2019 2018 2019 2018 2019 2018 Prior service cost (credit) $ — $ 7 $ (1,270 ) $ (1,738 ) $ — $ — Net actuarial loss 166,903 170,535 7,629 6,189 14,484 11,537 Total $ 166,903 $ 170,542 $ 6,359 $ 4,451 $ 14,484 $ 11,537 The following table presents amounts recognized by NW Holdings and NW Natural in AOCL and the changes in AOCL related to NW Natural's non-qualified employee benefit plans: Year Ended December 31, In thousands 2019 2018 Beginning balance $ (7,188 ) $ (8,438 ) Amounts reclassified to AOCL (3,611 ) 642 Amounts reclassified from AOCL: Amortization of actuarial losses 648 1,052 Reclassification of stranded tax effects (1) (1,366 ) — Total reclassifications before tax (4,329 ) 1,694 Tax expense (benefit) 784 (444 ) Total reclassifications for the period (3,545 ) 1,250 Ending balance $ (10,733 ) $ (7,188 ) (1) Reclassification of $1.4 million of income tax effects resulting from the TCJA from accumulated other comprehensive loss to retained earnings was made pursuant to the adoption of ASU 2018-02. See Note 2 . In 2020 , NW Natural will amortize an estimated $ 18.3 million from regulatory assets to net periodic benefit costs, consisting of $ 18.8 million of actuarial losses offset by $0.5 million of prior service credits. A total of $ 0.9 million will be amortized from AOCL to earnings related to actuarial losses in 2020 . The assumed discount rates for NW Natural's Pension Plan and other postretirement benefit plans were determined independently based on the FTSE Above Median Curve (discount rate curve), which uses high quality corporate bonds rated AA- or higher by S&P or Aa3 or higher by Moody’s. The discount rate curve was applied to match the estimated cash flows in each of the plans to reflect the timing and amount of expected future benefit payments for these plans. The assumed expected long-term rate of return on plan assets for the Pension Plan was developed using a weighted-average of the expected returns for the target asset portfolio. In developing the expected long-term rate of return assumption, consideration was given to the historical performance of each asset class in which the plan’s assets are invested and the target asset allocation for plan assets. The investment strategy and policies for Pension Plan assets held in the retirement trust fund were approved by the NW Natural Retirement Committee, which is composed of senior management with the assistance of an outside investment consultant. The policies set forth the guidelines and objectives governing the investment of plan assets. Plan assets are invested for total return with appropriate consideration for liquidity, portfolio risk, and return expectations. All investments are expected to satisfy the prudent investments rule under the Employee Retirement Income Security Act of 1974. The approved asset classes may include cash and short-term investments, fixed income, common stock and convertible securities, absolute and real return strategies, and real estate. Plan assets may be invested in separately managed accounts or in commingled or mutual funds. Investment re-balancing takes place periodically as needed, or when significant cash flows occur, in order to maintain the allocation of assets within the stated target ranges. The retirement trust fund is not currently invested in NW Holdings or NW Natural securities. The following table presents the Pension Plan asset target allocation at December 31, 2019 : Asset Category Target Allocation Long government/credit 20 % U.S. large cap equity 18 Non-U.S. equity 18 Absolute return strategies 12 U.S. small/mid cap equity 10 Real estate funds 7 High yield bonds 5 Emerging markets equity 5 Emerging market debt 5 Non-qualified supplemental defined benefit plan obligations were $ 38.3 million and $ 35.4 million at December 31, 2019 and 2018 , respectively. These plans are not subject to regulatory deferral, and the changes in actuarial gains and losses, prior service costs, and transition assets or obligations are recognized in AOCL, net of tax until they are amortized as a component of net periodic benefit cost. These are unfunded, non-qualified plans with no plan assets; however, a significant portion of the obligations is indirectly funded with company and trust-owned life insurance and other assets. Other postretirement benefit plans are unfunded plans but are subject to regulatory deferral. The actuarial gains and losses, prior service costs, and transition assets or obligations for these plans are recognized as a regulatory asset. Net periodic benefit costs consist of service costs, interest costs, the expected returns on plan assets, and the amortization of gains and losses and prior service costs. The gains and losses are the sum of the actuarial and asset gains and losses throughout the year and are amortized over the average remaining service period of active participants. The asset gains and losses are based in part on a market-related valuation of assets. The market-related valuation reflects differences between expected returns and actual investment returns with the differences recognized over a two-year period from the year in which they occur, thereby reducing year-to-year net periodic benefit cost volatility. The service cost component of net periodic benefit cost for NW Natural pension and other postretirement benefit plans is recognized in operations and maintenance expense in the consolidated statements of comprehensive income. The other non-service cost components are recognized in other income (expense), net in the consolidated statements of comprehensive income. The following table provides the components of net periodic benefit cost for NW Natural's pension and other postretirement benefit plans for the years ended December 31: Pension Benefits Other Postretirement Benefits In thousands 2019 2018 2017 2019 2018 2017 Service cost $ 6,308 $ 7,185 $ 7,090 $ 244 $ 282 $ 341 Interest cost 18,684 16,991 18,111 1,116 964 1,141 Expected return on plan assets (20,854 ) (20,639 ) (20,433 ) — — — Amortization of prior service costs 7 43 127 (468 ) (468 ) (468 ) Amortization of net actuarial loss 14,704 19,813 15,748 368 448 696 Net periodic benefit cost 18,849 23,393 20,643 1,260 1,226 1,710 Amount allocated to construction (2,493 ) (2,764 ) (6,597 ) (86 ) (98 ) (587 ) Amount deferred to regulatory balancing account — (10,314 ) (6,542 ) — — — Net periodic benefit cost charged to expense 16,356 10,315 7,504 1,174 1,128 1,123 Regulatory pension disallowance 10,500 — — — — — Amortization of regulatory balancing account 16,841 — — — — — Net amount charged to expense $ 43,697 $ 10,315 $ 7,504 $ 1,174 $ 1,128 $ 1,123 Net periodic benefit costs are reduced by amounts capitalized to NGD plant. In addition, a certain amount of net periodic benefit costs were recorded to the regulatory balancing account, representing net periodic pension expense for the Pension Plan above the amount set in rates, as approved by the OPUC, from 2011 through October 31, 2018. In March 2019, the OPUC issued an order concluding the NW Natural 2018 Oregon rate case. The order allowed for the application of certain deferred revenues and tax benefits from the TCJA to reduce NW Natural's pension regulatory balancing account. A corresponding total of $12.5 million in pension expenses were recognized in operating and maintenance expense and other income (expense), net in the consolidated statements of comprehensive income in the first quarter of 2019, with offsetting benefits recorded within operating revenues and income taxes. The order also directed NW Natural to reduce the balancing account by an additional $10.5 million , of which $3.9 million was charged to operations and maintenance expense and $6.6 million was charged to other income (expense), net in the consolidated statements of comprehensive income. Amortization of the remaining amount of the balancing account began in the second quarter of 2019 in accordance with the order. Total amortization of the regulatory balancing account of $16.8 million in 2019 , of which $6.2 million was charged to operations and maintenance expense and $10.6 million was charged to other income (expense), net. Total deferrals of the regulatory balancing account were $10.3 million in 2018 , of which $2.4 million was deferred from operations and maintenance expense and $7.9 million was deferred from other income (expense), net. The following table provides the assumptions used in measuring periodic benefit costs and benefit obligations for the years ended December 31: Pension Benefits Other Postretirement Benefits 2019 2018 2017 2019 2018 2017 Assumptions for net periodic benefit cost: Weighted-average discount rate 4.19 % 3.51 % 3.99 % 4.13 % 3.44 % 3.85 % Rate of increase in compensation 3.25-3.5% 3.25-4.5% 3.25-4.5% n/a n/a n/a Expected long-term rate of return 7.50 % 7.50 % 7.50 % n/a n/a n/a Assumptions for year-end funded status: Weighted-average discount rate 3.16 % 4.20 % 3.52 % 3.11 % 4.13 % 3.44 % Rate of increase in compensation (1) 3.50-6.50% 3.25-4.5% 3.25-4.5% n/a n/a n/a Expected long-term rate of return 7.25 % 7.50 % 7.50 % n/a n/a n/a (1) Rate assumption is 6.50% in 2020 and 3.50% thereafter. The 2020 compensation increase assumption was a result of the 2019 execution of a new collective bargaining agreement with unionized members of NW Natural effective December 1, 2019. The assumed annual increase in health care cost trend rates used in measuring other postretirement benefits as of December 31, 2019 was 6.50% . These trend rates apply to both medical and prescription drugs. Medical costs and prescription drugs are assumed to decrease gradually each year to a rate of 4.75% by 2026 . Assumed health care cost trend rates can have a significant effect on the amounts reported for the health care plans; however, other postretirement benefit plans have a cap on the amount of costs reimbursable by NW Natural. A one percentage point change in assumed health care cost trend rates would have the following effects: In thousands 1% Increase 1% Decrease Effect on net periodic postretirement health care benefit cost $ 49 $ (44 ) Effect on the accumulated postretirement benefit obligation 710 (640 ) Mortality assumptions are reviewed annually and are updated for material changes as necessary. In 2019, mortality rate assumptions were updated from RP-2014 mortality tables using scale MP-2018 to Pri-2012 mortality tables using scale MP-2019, which partially offset increases of the projected benefit obligation. The following table provides information regarding employer contributions and benefit payments for NW Natural's Pension Plan, non-qualified pension plans, and other postretirement benefit plans for the years ended December 31, and estimated future contributions and payments: In thousands Pension Benefits Other Benefits Employer Contributions: 2018 $ 17,715 $ 1,674 2019 13,310 1,774 2020 (estimated) 31,338 1,756 Benefit Payments: 2017 31,580 1,737 2018 21,918 1,674 2019 23,160 1,774 Estimated Future Benefit Payments: 2020 23,412 1,756 2021 24,304 1,833 2022 25,094 1,848 2023 25,941 1,899 2024 26,757 1,903 2025-2029 148,000 8,945 Employer Contributions to Company-Sponsored Defined Benefit Pension Plans NW Natural makes contributions to its qualified defined benefit Pension Plans based on actuarial assumptions and estimates, tax regulations, and funding requirements under federal law. The Pension Protection Act of 2006 (the Act) established funding requirements for defined benefit plans. The Act establishes a 100% funding target over seven years for plan years beginning after December 31, 2008. In July 2012, President Obama signed the Moving Ahead for Progress in the 21st Century Act (MAP-21) into law, which changed several provisions affecting pension plans, including temporary funding relief and Pension Benefit Guaranty Corporation (PBGC) premium increases, which shifts the level of minimum required contributions from the short-term to the long-term as well as increasing the operational costs of running a pension plan. MAP-21 established a new minimum and maximum corridor for segment rates based on a 25-year average of bond yields, which resulted in lower minimum contributions requirements than those under previous regulations. MAP-21, as amended, provides for the current corridor to be in effect through 2020 and subsequently broaden on an annual basis from 2021 through 2024. The Pension Plan was underfunded by $ 164.3 million at December 31, 2019 . NW Natural made cash contributions totaling $ 11.0 million to its Pension Plan for 2019 . During 2020 , NW Natural expects to make contributions of approximately $29.0 million to this plan. Multiemployer Pension Plan In addition to the NW Natural-sponsored Pension Plan presented above, prior to 2014 NW Natural contributed to a multiemployer pension plan for its NGD union employees known as the Western States Office and Professional Employees International Union Pension Fund (Western States Plan). That plan's employer identification number is 94-6076144. Effective December 22, 2013, NW Natural withdrew from the plan, which was a noncash transaction. Vested participants will receive all benefits accrued through the date of withdrawal. As the plan was underfunded at the time of withdrawal, NW Natural was assessed a withdrawal liability of $8.3 million , plus interest, which requires NW Natural to pay $0.6 million each year to the plan for 20 years beginning in July 2014. The cost of the withdrawal liability was deferred to a regulatory account on the balance sheet. Payments were $0.6 million for 2019 , and as of December 31, 2019 the liability balance was $6.5 million . Contributions to the plan were $0.6 million for each of 2018 and 2017, which was approximately 5% to 6% of the total contributions to the plan by all employer participants in those years. Defined Contribution Plan NW Natural's Retirement K Savings Plan is a qualified defined contribution plan under Internal Revenue Code Sections 401(a) and 401(k). NW Natural contributions totaled $ 7.0 million , $6.5 million , and $5.4 million for 2019 , 2018 , and 2017 , respectively. The Retirement K Savings Plan includes an Employee Stock Ownership Plan. Deferred Compensation Plans NW Natural's supplemental deferred compensation plans for eligible officers and senior managers are non-qualified plans. These plans are designed to enhance the retirement savings of employees and to assist them in strengthening their financial security by providing an incentive to save and invest regularly. Fair Value Below is a description of the valuation methodologies used for assets measured at fair value. In cases where NW Natural's Pension Plan is invested through a collective trust fund or mutual fund, the fund's market value is utilized. Market values for investments directly owned are also utilized. U.S. EQUITY. These are non-published net asset value (NAV) assets. The non-published NAV assets consist of commingled trusts where NAV is not published but the investment can be readily disposed of at NAV or market value. The underlying investments in this asset class includes investments primarily in U.S. common stocks. INTERNATIONAL/GLOBAL EQUITY. These are Level 1 and non-published NAV assets. The Level 1 asset is a mutual fund, and the non-published NAV assets consist of commingled trusts where the NAV/unit price is not published, but the investment can be readily disposed of at the NAV/unit price. The mutual funds has a readily determinable fair value, including a published NAV, and the commingled trusts are valued at unit price. This asset class includes investments primarily in foreign equity common stocks. LIABILITY HEDGING. These are non-published NAV assets. The non-published NAV assets consist of commingled trusts where NAV is not published but the investment can be readily disposed of at NAV or market value. The underlying investments in this asset class include long duration fixed income investments primarily in U.S. treasuries, U.S. government agencies, municipal securities, mortgage-backed securities, asset-backed securities, as well as U.S. and international investment-grade corporate bonds. OPPORTUNISTIC. These are non-published NAV assets consisting of commingled trusts where the investments can be readily disposed of at unit price, and a hedge fund of funds where the valuation is not published. This hedge fund of funds is winding down. Based on recent dispositions, NW Natural believes the remaining investment is fairly valued. The hedge fund of funds is valued at the weighted average value of investments in various hedge funds, which in turn are valued at the closing price of the underlying securities. This asset class includes investments in emerging market debt, leveraged loans, REITs, high yield bonds, a commodities fund, and a hedge fund of funds . ABSOLUTE RETURN STRATEGY. This is a non-published NAV asset consisting of a hedge fund of funds where the valuation is not published. This hedge fund of funds is winding down. Based on recent dispositions, NW Natural believes the remaining investment is fairly valued. The hedge fund of funds is valued at the weighted average value of investments in various hedge funds, which in turn are valued at the closing price of the underlying securities. This asset class primarily includes investments in common stocks and fixed income securities. CASH AND CASH EQUIVALENTS. These are Level 1 and non-published NAV assets. The Level 1 assets consist of cash in U.S. dollars, which can be readily disposed of at face value. The non-published NAV assets represent mutual funds without published NAV's but the investment can be readily disposed of at the NAV. The mutual funds are valued at the NAV of the shares held by the plan at the valuation date. The preceding valuation methods may produce a fair value calculation that is not indicative of net realizable value or reflective of future fair values. Although we believe these valuation methods are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain investments could result in a different fair value measurement at the reporting date. Investment securities are exposed to various financial risks including interest rate, market, and credit risks. Due to the level of risk associated with certain investment securities, it is reasonably possible that changes in the values of NW Natural's investment securities will occur in the near term and such changes could materially affect NW Natural's investment account balances and the amounts reported as plan assets available for benefit payments. The following tables present the fair value of NW Natural's plan assets, including outstanding receivables and liabilities, of NW Natural's retirement trust fund: In thousands December 31, 2019 Investments Level 1 Level 2 Level 3 Non-Published NAV (1) Total US equity $ — $ — $ — $ 95,604 $ 95,604 International / Global equity 33,168 — — 74,337 107,505 Liability hedging — — — 93,028 93,028 Opportunistic — — — 9,864 9,864 Cash and cash equivalents — — — 7,049 7,049 Total investments $ 33,168 $ — $ — $ 279,882 $ 313,050 December 31, 2018 Investments Level 1 Level 2 Level 3 Non-Published NAV (1) Total US equity $ — $ — $ — $ 85,233 $ 85,233 International / Global equity 24,994 — — 70,017 95,011 Liability hedging — — — 45,659 45,659 Opportunistic — — — 23,186 23,186 Cash and cash equivalents — — — 8,707 8,707 Total investments $ 24,994 $ — $ — $ 232,802 $ 257,796 December 31, 2019 2018 Receivables: Accrued interest and dividend income $ 3,243 $ 1 Due from broker for securities sold — — Total receivables 3,243 1 Liabilities: Due to broker for securities purchased 3,242 — Total investment in retirement trust $ 313,051 $ 257,797 (1) The fair value for these investments is determined using Net Asset Value per share (NAV) as of December 31, as a practical expedient, and therefore they are not classified within the fair value hierarchy. These investments primarily consist of institutional investment products, for which the NAV is generally not publicly available.

Income Tax

Income Tax	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income Tax [Text Block]	INCOME TAX The following table provides a reconciliation between income taxes calculated at the statutory federal tax rate and the provision for income taxes reflected in the NW Holdings and NW Natural statements of comprehensive income or loss for December 31: NW Holdings NW Natural Dollars in thousands 2019 2018 2017 2019 2018 2017 Income taxes at federal statutory rate $ 16,370 $ 19,222 $ 39,578 $ 17,438 $ 19,434 $ 39,624 Increase (decrease): State income tax, net of federal 4,422 4,927 5,066 4,716 4,982 5,072 Differences required to be flowed-through by regulatory commissions (5,772 ) 1,302 2,357 (5,772 ) 1,302 2,357 Effect of the TCJA — — (3,376 ) — — (2,956 ) Deferred tax rate differential post-TCJA — (76 ) — — (75 ) — Regulatory settlement (1,129 ) — — (1,129 ) — — Other, net (1,249 ) (1,184 ) (2,617 ) (1,188 ) (1,184 ) (2,619 ) Total provision for income taxes $ 12,642 $ 24,191 $ 41,008 $ 14,065 $ 24,459 $ 41,478 Effective tax rate 16.2 % 26.4 % 36.3 % 16.9 % 26.4 % 36.6 % The NW Holdings and NW Natural effective income tax rates for 2019 compared to 2018 changed primarily as a result of lower pre-tax income and amortization of excess deferred income tax benefits as ordered by regulatory commissions. The NW Holdings and NW Natural effective income tax rates for 2018 compared to 2017 changed primarily as a result of the lower federal corporate income tax rate provided for by the TCJA . The provision for current and deferred income taxes consists of the following at December 31: NW Holdings NW Natural In thousands 2019 2018 2017 2019 2018 2017 Current Federal $ 5,530 $ 8,953 $ 19,345 $ 6,755 $ 9,127 $ 19,304 State 1,667 3,785 5,963 2,101 3,846 5,956 7,197 12,738 25,308 8,856 12,973 25,260 Deferred Federal 1,515 9,001 13,869 1,340 9,025 14,371 State 3,930 2,452 1,831 3,869 2,461 1,847 5,445 11,453 15,700 5,209 11,486 16,218 Income tax provision $ 12,642 $ 24,191 $ 41,008 $ 14,065 $ 24,459 $ 41,478 The following table summarizes the tax effect of significant items comprising NW Holdings and NW Natural's deferred income tax balances recorded at December 31: NW Holdings NW Natural In thousands 2019 2018 2019 2018 Deferred tax liabilities: Plant and property $ 269,886 $ 288,385 $ 281,044 $ 303,186 Leases receivable 40,133 — 40,133 — Pension and postretirement obligations 22,635 27,135 22,635 27,135 Income tax regulatory asset 19,382 21,403 19,382 21,402 Other 751 1,061 410 537 Total deferred income tax liabilities $ 352,787 $ 337,984 $ 363,604 $ 352,260 Deferred income tax assets: Income tax regulatory liability $ 54,259 $ 57,469 $ 54,259 $ 57,469 Other intangible assets 2,723 — — — Net operating losses and credits carried forward 162 52 48 52 Total deferred income tax assets $ 57,144 $ 57,521 $ 54,307 $ 57,521 Total net deferred income tax liabilities $ 295,643 $ 280,463 $ 309,297 $ 294,739 At December 31, 2019 and 2018 , regulatory income tax assets of $16.9 million and $19.1 million , respectively, were recorded by NW Natural, a portion of which is recorded in current assets. These regulatory income tax assets primarily represent future rate recovery of deferred tax liabilities, resulting from differences in NGD plant financial statement and tax bases and NGD plant removal costs, which were previously flowed through for rate making purposes and to take into account the additional future taxes, which will be generated by that recovery. These deferred tax liabilities, and the associated regulatory income tax assets, are currently being recovered through customer rates. At December 31, 2019 and 2018 , regulatory income tax assets of $2.5 million and $2.3 million , respectively, were recorded by NW Natural, representing future recovery of deferred tax liabilities resulting from the equity portion of AFUDC. At December 31, 2019 and 2018 , deferred tax assets of $54.3 million and $57.5 million , respectively, were recorded by NW Natural representing the future income tax benefit associated with the excess deferred income tax regulatory liability recorded as a result of the lower federal corporate income tax rate provided for by the TCJA. At December 31, 2019 and 2018 , regulatory liability balances representing the benefit of the change in deferred taxes as a result of the TCJA of $205.0 million and $217.1 million , respectively, were recorded by NW Natural. NW Natural’s natural gas utility rates include an allowance to provide for the recovery of the anticipated provision for income taxes incurred as a result of providing regulated services. As a result of the 21 percent federal corporate income tax rate enacted in 2017, NW Natural recorded an additional regulatory liability in 2018 and 2019 reflecting the deferral of the estimated rate benefit for customers. The deferral period for Oregon ended on October 31, 2018 coincident with new rates beginning November 1, 2018. The deferral period for Washington ended on October 31, 2019 coincident with new rates beginning November 1, 2019. At December 31, 2019 and 2018, a regulatory liability of $1.7 million and $8.2 million , respectively, was recorded to reflect this estimated revenue deferral. NW Holdings and NW Natural assess the available positive and negative evidence to estimate if sufficient taxable income will be generated to utilize their respective existing deferred tax assets. Based upon this assessment, NW Holdings and NW Natural determined that it is more likely than not that all of their respective deferred tax assets recorded as of December 31, 2019 will be realized. The Company estimates it has net operating loss (NOL) carryforwards of $0.4 million for federal taxes and $0.4 million for Oregon taxes at December 31, 2019. We anticipate fully utilizing these NOL carryforward balances before they begin to expire in 2027 for federal and 2022 for Oregon. California alternative minimum tax (AMT) credits of $0.1 million are also available. The AMT credits do not expire. Uncertain tax positions are accounted for in accordance with accounting standards that require an assessment of the anticipated settlement outcome of material uncertain tax positions taken in a prior year, or planned to be taken in the current year. Until such positions are sustained, the uncertain tax benefits resulting from such positions would not be recognized. No reserves for uncertain tax positions were recorded as of December 31, 2019, 2018, or 2017. The federal income tax returns for tax years 2015 and earlier are closed by statute. The IRS Compliance Assurance Process (CAP) examination of the 2016 and 2017 tax years have been completed. There were no material changes to these returns as filed. The 2018 and 2019 tax years are currently under IRS CAP examination. Our 2020 CAP application has been filed. Under the CAP program, NW Holdings and NW Natural work with the IRS to identify and resolve material tax matters before the tax return is filed each year. As of December 31, 2019, income tax years 2015 through 2018 remain open for examination by the State of California. Income tax year 2018 is open for examination by the State of Idaho. The State of Oregon examined the Oregon corporate income tax returns for tax years 2015, 2016, and 2017. No material changes occurred as a result of this examination. U.S. Federal TCJA Matters On December 22, 2017, the TCJA was enacted and permanently lowered the U.S. federal corporate income tax rate to 21% from the previous maximum rate of 35% , effective for the tax year beginning January 1, 2018. The TCJA included specific provisions related to regulated public utilities that provide for the continued deductibility of interest expense and the elimination of bonus tax depreciation for property both acquired and placed into service on or after January 1, 2018. Under pre-TCJA law, business interest was generally deductible in the determination of taxable income. The TCJA imposed a new limitation on the deductibility of net business interest expense in excess of approximately 30 percent of adjusted taxable income. Taxpayers operating in the trade or business of a regulated utility are excluded from these new interest expense limitations. Proposed U.S. Treasury Regulations were published in November of 2018 which provide a de minimis rule whereby if 90 percent or more of a taxpayer's adjusted asset basis is allocable to regulated utility activities, then all of the business interest expense of that taxpayer is deemed to be excepted business interest of the regulated utility activity and is thereby not limited under the TCJA. As a result of the de minimis rule, NW Holdings and NW Natural anticipate that business interest expense will not be limited under the TCJA. The TCJA generally provides for immediate full expensing for qualified property both acquired and placed in service after September 27, 2017 and before January 1, 2023. This would generally provide for accelerated cost recovery for capital investments. However, the definition of qualified property excludes property used in the trade or business of a regulated utility. Final U.S. Treasury Regulations were published in September of 2019 which clarified that bonus tax depreciation would not be available for regulated utility activity assets both acquired and placed in service by NW Holdings or NW Natural on or after January 1, 2018. Proposed U.S. Treasury Regulations released in September of 2019 indicated that long production period property acquired before September 27, 2017 continues to qualify for bonus depreciation in the year placed in service consistent with pre-TCJA law. The SEC staff previously issued Staff Accounting Bulletin 118, which provided guidance on accounting for the tax effects of the TCJA. SAB 118 provided a measurement period that should not extend beyond one year from the TCJA enactment date for companies to complete the accounting for the TCJA under ASC 740. To the extent that a company’s accounting for certain income tax effects of the TCJA was incomplete but a reasonable estimate could be made, a company would record a provisional estimate in the financial statements. NW Natural previously disclosed that due to uncertainties with respect to the availability of bonus tax depreciation for regulated utility activity assets under the TCJA that the effects of bonus tax depreciation for assets placed in service after September 27, 2017 but before January 1, 2018 had not been recorded. The determination to exclude all assets placed in service after September 27, 2017 but before January 1, 2018 from bonus tax depreciation was provisional as provided for under SAB 118. As a result of the Proposed Regulations on bonus tax depreciation published in August of 2018, NW Natural revised the provisional estimate of deferred taxes and income taxes payable to reflect the effects of bonus tax depreciation for assets placed in service after September 27, 2017 but before January 1, 2018. In the third quarter of 2018, NW Natural recognized increases to prepaid income tax of $7.4 million , deferred income tax liability of $4.1 million , and regulatory liability of $3.3 million . In the fourth quarter of 2018, NW Natural recognized additional increases to prepaid income tax of $0.5 million , deferred income tax liability of $0.3 million , and regulatory liability of $0.2 million . The accounting for income tax effects of the TCJA was complete at the end of calendar year 2018. NW Natural previously filed applications with the OPUC and WUTC to defer the NGD net income tax benefits resulting from the TCJA. In March 2019, the OPUC issued an order addressing the regulatory amortization of the income tax benefits from the TCJA that NW Natural deferred for Oregon customers in December of 2017. Under the order, NW Natural will provide the benefit of these TCJA income tax deferrals to Oregon customers through ongoing annual credits to customer base rates and as a one-time recovery of a portion of the pension balancing account regulatory asset balance. On an annualized basis, it is anticipated that the income tax benefits from the provision of these TCJA benefits to customers should approximate the reduction to pretax income that occurs as a result of the customer base rate credits and one-time recovery of a portion of the pension balancing account. In October 2019, the WUTC issued an order addressing the regulatory amortization of the income tax benefits from the TCJA that NW Natural deferred for Washington customers in December of 2017. Under the order, NW Natural will provide deferred income tax benefits from the TCJA to customers through base rate credits beginning November 1, 2019.

Property, Plant and Equipment

Property, Plant and Equipment	12 Months Ended
	Dec. 31, 2019
Public Utilities, Property, Plant and Equipment [Abstract]
Property, Plant and Equipment [Text Block]	PROPERTY, PLANT, AND EQUIPMENT The following table sets forth the major classifications of property, plant, and equipment and accumulated depreciation of continuing operations at December 31: In thousands 2019 2018 NW Natural: NGD plant in service $ 3,302,049 $ 3,134,122 NGD work in progress 84,965 204,978 Less: Accumulated depreciation 1,017,931 974,252 NGD plant, net 2,369,083 2,364,848 Other plant in service 63,513 66,009 Other construction work in progress 5,548 5,330 Less: Accumulated depreciation 18,662 18,603 Other plant, net (1) 50,399 52,736 Total property, plant, and equipment $ 2,419,482 $ 2,417,584 Other (NW Holdings): Other plant in service $ 20,671 $ 4,051 Less: Accumulated depreciation 1,254 263 Other plant, net (1) 19,417 3,788 NW Holdings: Total property, plant, and equipment $ 2,438,899 $ 2,421,372 NW Natural and NW Holdings: Capital expenditures in accrued liabilities $ 32,502 $ 23,676 (1) NW Natural previously reported other balances which were restated due to certain assets and liabilities now being classified as discontinued operations assets and liabilities in its balance sheets. See Note 19 for further discussion. Accumulated depreciation does not include the accumulated provision for asset removal costs of $401.9 million and $380.5 million at December 31, 2019 and 2018 , respectively. These accrued asset removal costs are reflected on the balance sheet as regulatory liabilities. See Note 2 . During 2019 and 2018 , no equipment was acquired under capital leases. NW Holdings Other plant balances include long-lived assets associated with water operations and non-regulated activities not held by NW Natural or its subsidiaries. NW Natural Other plant balances include long-lived assets not related to NGD and long-lived assets that may be used to support NGD operations. The weighted average depreciation rate for NGD assets was 2.9% during 2019 and 2.8% during 2018 , and 2017 . The weighted average depreciation rate for assets not related to NGD was 1.8% in 2019 , 2.2% in 2018 , and 1.9% in 2017 . In October 2017, NW Natural entered into a 20 -year lease agreement expected to commence in 2020 for its new corporate operations center location in Portland, Oregon. Under the new lease standard, NW Natural is no longer considered the accounting owner of the asset during construction. As such, the build to suit asset and liability balances at December 31, 2018 of $26.0 million were derecognized in January 2019. The previous build to suit balances were recorded under ASC 840 within property, plant and equipment and other non-current liabilities in the consolidated balance sheet. In May 2019, NW Natural placed its North Mist gas storage expansion facility into service and commenced storage services to the facility's single customer, PGE. Under U.S. GAAP, this agreement is classified as a sales-type lease and qualifies for regulatory accounting deferral treatment. Accordingly, the project was de-recognized from property, plant and equipment upon lease commencement and the investment balance is presented net of the current portion of scheduled billings within assets under sales-type leases on the consolidated balance sheets. A total of $146.0 million was de-recognized from plant on the lease commencement date. The facility is included within rate base for ratemaking purposes. See Note 7 for information regarding leases, including North Mist.

Gas Reserves

Gas Reserves	12 Months Ended
	Dec. 31, 2019
Gas Reserves [Abstract]
Gas Reserves [Text Block]	GAS RESERVES NW Natural has invested $188 million through the gas reserves program in the Jonah Field located in Wyoming as of December 31, 2019 . Gas reserves are stated at cost, net of regulatory amortization, with the associated deferred tax benefits recorded as liabilities in the consolidated balance sheets. The investment in gas reserves provides long-term price protection for NGD customers through the original agreement with Encana Oil & Gas (USA) Inc. under which NW Natural invested $178 million and the amended agreement with Jonah Energy LLC under which an additional $10 million was invested. NW Natural entered into the original agreements with Encana in 2011 under which NW Natural holds working interests in certain sections of the Jonah Field. Gas produced in these sections is sold at prevailing market prices, and revenues from such sales, net of associated operating and production costs and amortization, are credited to the NGD cost of gas. The cost of gas, including a carrying cost for the rate base investment, is included in the annual Oregon PGA filing, which allows NW Natural to recover these costs through customer rates. The investment under the original agreement, less accumulated amortization and deferred taxes, earns a rate of return. In March 2014, NW Natural amended the original gas reserves agreement in order to facilitate Encana's proposed sale of its interest in the Jonah field to Jonah Energy. Under the amendment, NW Natural ended the drilling program with Encana, but increased its working interests in its assigned sections of the Jonah field. NW Natural also retained the right to invest in new wells with Jonah Energy. Under the amended agreement there is still the option to invest in additional wells on a well-by-well basis with drilling costs and resulting gas volumes shared at NW Natural's amended proportionate working interest for each well in which it invests. NW Natural elected to participate in some of the additional wells drilled in 2014, but has not participated in additional wells since 2014. However, there may be the opportunity to participate in more wells in the future. Gas produced from the additional wells is included in the Oregon PGA at a fixed rate of $0.4725 per therm, which approximates the 10-year hedge rate plus financing costs at the inception of the investment. Gas reserves acted to hedge the cost of gas for approximately 5% , 6% and 6% of NGD gas supplies for the years ended December 31, 2019 , 2018 , and 2017 respectively. The following table outlines NW Natural's net gas reserves investment at December 31: In thousands 2019 2018 Gas reserves, current $ 15,278 $ 16,647 Gas reserves, non-current 172,029 170,660 Less: Accumulated amortization 123,635 104,463 Total gas reserves (1) 63,672 82,844 Less: Deferred taxes on gas reserves 15,515 20,071 Net investment in gas reserves $ 48,157 $ 62,773 (1) The net investment in additional wells included in total gas reserves was $3.8 million and $4.8 million at December 31, 2019 and 2018 , respectively. NW Natural's investment is included in NW Holdings' and NW Natural's consolidated balance sheets under gas reserves with the maximum loss exposure limited to the investment balance.

Investments

Investments	12 Months Ended
	Dec. 31, 2019
Investments [Abstract]
Investments	14. INVESTMENTS Investments include financial investments in life insurance policies, and equity method investments in certain partnerships and limited liability companies. The following table summarizes other investments at December 31: NW Holdings NW Natural In thousands 2019 2018 2019 2018 Investments in life insurance policies $ 49,837 $ 49,922 $ 49,837 $ 49,922 Investments in gas pipeline 13,472 13,571 — — Other 24 65 — — Total other investments $ 63,333 $ 63,558 $ 49,837 $ 49,922 Investment in Life Insurance Policies NW Natural has invested in key person life insurance contracts to provide an indirect funding vehicle for certain long-term employee and director benefit plan liabilities. The amount in the above table is reported at cash surrender value, net of policy loans. Investments in Gas Pipeline Trail West Pipeline, LLC (TWP), a wholly-owned subsidiary of TWH, is pursuing the development of a new gas transmission pipeline that would provide an interconnection with NW Natural's NGD system. NWN Energy, a wholly-owned subsidiary of NW Holdings, owns 50% of TWH, and 50% is owned by TransCanada American Investments Ltd., an indirect wholly-owned subsidiary of TransCanada Corporation. Variable Interest Entity (VIE) Analysis TWH is a VIE, with NW Holdings' investment in TWP reported under equity method accounting. It has been determined that NW Holdings is not the primary beneficiary of TWH’s activities as it only has a 50% share of the entity, and there are no stipulations that allow NW Holdings a disproportionate influence over it. Investments in TWH and TWP are included in other investments on NW Holdings' balance sheet. If this investment is not developed, then the maximum loss exposure related to TWH is limited to NW Holdings' equity investment balance, less its share of any cash or other assets available to NW Holdings as a 50% owner. The investment balance in TWH was $13.4 million at December 31, 2019 and 2018 . Impairment Analysis Investments in nonconsolidated entities accounted for under the equity method are reviewed for impairment at each reporting period and following updates to our corporate planning assumptions. If it is determined a loss in value is other than temporary, a charge is recognized for the difference between the investment’s carrying value and its estimated fair value. Fair value is based on quoted market prices when available or on the present value of expected future cash flows. Differing assumptions could affect the timing and amount of a charge recorded in any period. In 2011, TWP withdrew its original application with the FERC for a proposed natural gas pipeline in Oregon and informed FERC that it intended to re-file an application to reflect changes in the project scope aligning the project with the region’s current and future gas infrastructure needs. TWP continues working with customers in the Pacific Northwest to further understand their gas transportation needs and determine the commercial support for a revised pipeline proposal. A new FERC certificate application is expected to be filed to reflect a revised scope based on these regional needs. NW Holdings' equity investment was not impaired at December 31, 2019 as the fair value of expected cash flows from planned development exceeded NW Holdings' remaining equity investment of $ 13.4 million at December 31, 2019 . However, if NW Holdings learns that the project is not viable or will not go forward, it could be required to recognize a maximum charge of up to approximately $ 13.4 million based on the current amount of the equity investment, net of cash and working capital at TWP. NW Holdings will continue to monitor and update the impairment analysis as required.

Business Combinations Business

Business Combinations Business Combinations	12 Months Ended
	Dec. 31, 2019
Business Combinations [Abstract]
Business Combinations	BUSINESS COMBINATIONS 2019 Business Combinations Sunriver On May 31, 2019 , NWN Water of Oregon, a wholly-owned indirect subsidiary of NW Holdings, completed the acquisition of Sunriver Water and Sunriver Environmental (collectively referred to as Sunriver), a privately-owned water utility and wastewater treatment company located in Sunriver, Oregon that serves approximately 9,400 connections. The acquisition-date fair value of the total consideration transferred, after closing adjustments, was approximately $55.0 million in cash consideration. The transaction aligns with NW Holdings' water sector strategy as it continues to expand its water utility service territory in the Pacific Northwest and begins to pursue wastewater investment opportunities. The Sunriver acquisition met the criteria of a business combination, and as such a preliminary allocation of the consideration to the acquired assets based on their estimated fair value as of the acquisition date was performed. In accordance with U.S. GAAP, the fair value determination was made using existing regulatory conditions for assets associated with Sunriver Water, LLC as well as existing market conditions and standard valuation approaches for assets associated with Sunriver Environmental, LLC in order to allocate value as determined by an independent third party assessor for certain assets, which involved the use of management judgment in determining the significant estimates and assumptions used by the assessor, with the remaining difference from the consideration transferred being recorded as goodwill. This allocation is considered preliminary as of December 31, 2019 , as facts and circumstances that existed as of the acquisition date may be discovered as we continue to integrate Sunriver. As a result, subsequent adjustments to the preliminary valuation of tangible assets, contract assets and liabilities, tax positions, and goodwill may be required. Subsequent adjustments are not expected to be significant, and any such adjustments are expected to be completed within the one-year measurement period. The acquisition costs were expensed as incurred. Preliminary goodwill of $40.1 million was recognized from this acquisition. The goodwill recognized is attributable to Sunriver's regulated water utility service territory, experienced workforce, and the strategic benefits for both the water utility and wastewater services expected from growth in its service territory. No intangible assets aside from goodwill were acquired. The total amount of goodwill that is expected to be deductible for income tax purposes is approximately $50.2 million . The preliminary purchase price for the acquisition has been allocated to the net assets acquired as of the acquisition date and is as follows: In thousands December 31, 2019 Current assets $ 221 Property, plant and equipment 13,819 Goodwill 40,118 Deferred tax assets 812 Current liabilities (22 ) Total net assets acquired $ 54,948 The amount of Sunriver revenues included in NW Holdings' consolidated statements of comprehensive income is $3.7 million for the year ended December 31, 2019. Earnings from Sunriver activities for the year ended December 31, 2019 were not material to the results of NW Holdings. Other Acquisitions During the year ended December 31, 2019, NWN Water completed three additional acquisitions qualifying as business combinations. The aggregate fair value of the preliminary consideration transferred for these acquisitions was approximately $2.0 million . These business combinations were not significant to NW Holdings' results of operations. 2018 Business Combinations Falls Water On September 13, 2018 , NWN Water, then a wholly-owned subsidiary of NW Natural and now a wholly-owned subsidiary of NW Holdings, completed the acquisition of Falls Water, a privately-owned water utility in the Pacific Northwest for non-cash consideration of $8.5 million , in the form of 125,000 shares of NW Natural common stock, which were converted to NW Holdings common stock in our October 1, 2018 reorganization. Falls Water became a wholly-owned subsidiary of NWN Water and marked its first acquisition in the water utility sector. This acquisition aligns with NW Holdings' water sector strategy as the acquisition provides NWN Water entry into Idaho, expands service area, and opens further opportunity for growth. Falls Water is based in Idaho Falls, Idaho and served approximately 5,300 connections at the time of acquisition. Through the purchase of all of the outstanding shares of Falls Water, NWN Water acquired the net assets and 100% control of Falls Water. We determined that the Falls Water acquisition met the criteria of a business combination, and as such performed an allocation of the consideration to the acquired assets and assumed liabilities based on their fair value as of the acquisition date, the majority of which was allocated to goodwill. The acquisition costs were insignificant and were expensed as incurred. The results of Falls Water are not material to the consolidated financial results of NW Holdings. Goodwill of $6.2 million was recognized from this acquisition and is attributable to Falls Water's regulated service territory and experienced workforce as well as the strategic benefits expected from this high-growth service territory. NW Holdings has included this goodwill in other for segment reporting purposes, and it is not deductible for income tax purposes. No intangible assets aside from goodwill were acquired. See Note 2 for goodwill impairment information. Other Acquisitions During 2018, in addition to the Falls Water acquisition, NWN Water completed three acquisitions qualifying as business combinations. The aggregate fair value of the consideration transferred for these acquisitions was approximately $2.8 million . These business combinations, both individually and in aggregate, were not significant to NW Holdings' results of operations. As a result of all acquisitions completed, total goodwill was $49.9 million and $9.0 million as of December 31, 2019 and 2018, respectively. The increase in the goodwill balance was due to additions associated with our acquisitions in the water sector. All of our goodwill is related to water and wastewater acquisitions and is included in the other category for segment reporting purposes. The annual impairment assessment of goodwill occurs in the fourth quarter of each year. There have been no impairments recognized to date.

Derivative Instruments

Derivative Instruments	12 Months Ended
	Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments	DERIVATIVE INSTRUMENTS NW Natural enters into financial derivative contracts to hedge a portion of the NGD segment’s natural gas sales requirements. These contracts include swaps, options, and combinations of option contracts. These derivative financial instruments are primarily used to manage commodity price variability. A small portion of NW Natural's derivative hedging strategy involves foreign currency exchange contracts. NW Natural enters into these financial derivatives, up to prescribed limits, primarily to hedge price variability related to physical gas supply contracts as well as to hedge spot purchases of natural gas. The foreign currency forward contracts are used to hedge the fluctuation in foreign currency exchange rates for pipeline demand charges paid in Canadian dollars. In the normal course of business, NW Natural also enters into indexed-price physical forward natural gas commodity purchase contracts and options to meet the requirements of NGD customers. These contracts qualify for regulatory deferral accounting treatment. NW Natural also enters into exchange contracts related to the third-party asset management of its gas portfolio, some of which are derivatives that do not qualify for hedge accounting or regulatory deferral, but are subject to NW Natural's regulatory sharing agreement. These derivatives are recognized in operating revenues, net of amounts shared with NGD customers. Notional Amounts The following table presents the absolute notional amounts related to open positions on NW Natural derivative instruments: At December 31, In thousands 2019 2018 Natural gas (in therms): Financial 651,540 408,850 Physical 512,849 472,275 Foreign exchange $ 6,650 $ 6,936 Purchased Gas Adjustment (PGA) Derivatives entered into by NW Natural for the procurement or hedging of natural gas for future gas years generally receive regulatory deferral accounting treatment. In general, commodity hedging for the current gas year is completed prior to the start of the gas year, and hedge prices are reflected in the weighted-average cost of gas in the PGA filing. Rates and hedging approaches may vary between states due to different rate structures and mechanisms. In addition, as required with the Washington PGA filing, NW Natural incorporated and began implementing risk-responsive hedging strategies for the 2019-20 PGA for its Washington gas supplies. Hedge contracts entered into after the start of the PGA period are subject to the PGA incentive sharing mechanism in Oregon. NW Natural entered the 2019-20 and 2018-19 gas years with forecasted sales volumes hedged at 52% and 48% in financial swap and option contracts, and 19% and 24% in physical gas supplies, respectively. Hedge contracts entered into prior to the PGA filing, in September 2019, were included in the PGA for the 2019-20 gas year. Hedge contracts entered into after the PGA filing, and related to subsequent gas years, may be included in future PGA filings and qualify for regulatory deferral. Unrealized and Realized Gain/Loss The following table reflects the income statement presentation for the unrealized gains and losses from NW Natural's derivative instruments, which also represents all derivative instruments at NW Holdings: December 31, 2019 December 31, 2018 In thousands Natural gas commodity Foreign exchange Natural gas commodity Foreign exchange Benefit (expense) to cost of gas $ 9,863 $ 102 $ (1,239 ) $ (284 ) Operating revenues (expense) (568 ) — 1,660 — Amounts deferred to regulatory accounts on balance sheet (9,376 ) (102 ) (211 ) 284 Total gain (loss) in pre-tax earnings $ (81 ) $ — $ 210 $ — UNREALIZED GAIN/LOSS. Outstanding derivative instruments related to regulated NGD operations are deferred in accordance with regulatory accounting standards. The cost of foreign currency forward and natural gas derivative contracts are recognized immediately in the cost of gas; however, costs above or below the amount embedded in the current year PGA are subject to a regulatory deferral tariff and therefore, are recorded as a regulatory asset or liability. REALIZED GAIN/LOSS. NW Natural realized net gains of $ 17.9 million and net gains of $7.4 million for the years ended December 31, 2019 and 2018 , respectively, from the settlement of natural gas financial derivative contracts. Realized gains and losses offset the higher or lower cost of gas purchased, resulting in no incremental amounts to collect or refund to customers. Credit Risk Management of Financial Derivatives Instruments No collateral was posted with or by NW Natural counterparties as of December 31, 2019 or 2018 . NW Natural attempts to minimize the potential exposure to collateral calls by diversifying counterparties to manage liquidity risk. Counterparties generally allow a certain credit limit threshold before requiring NW Natural to post collateral against loss positions. Given NW Natural's counterparty credit limits and portfolio diversification, it was not subject to collateral calls in 2019 or 2018 . The collateral call exposure is set forth under credit support agreements, which generally contain credit limits. NW Natural could also be subject to collateral call exposure where it has agreed to provide adequate assurance, which is not specific as to the amount of credit limit allowed, but could potentially require additional collateral in the event of a material adverse change. Based upon current commodity financial swap and option contracts outstanding, which reflect unrealized gains of $ 5.6 million at December 31, 2019 , we have estimated the level of collateral demands, with and without potential adequate assurance calls, using current gas prices and various credit downgrade rating scenarios for NW Natural as follows: Credit Rating Downgrade Scenarios In thousands (Current Ratings) A+/A3 BBB+/Baa1 BBB/Baa2 BBB-/Baa3 Speculative With Adequate Assurance Calls $ — $ — $ — $ — $ (66 ) Without Adequate Assurance Calls — — — — (66 ) NW Natural's financial derivative instruments are subject to master netting arrangements; however, they are presented on a gross basis in the consolidated balance sheets. NW Natural and its counterparties have the ability to set-off obligations to each other under specified circumstances. Such circumstances may include a defaulting party, a credit change due to a merger affecting either party, or any other termination event. If netted by counterparty, NW Natural's physical and financial derivative position would result in an asset of $9.4 million and a liability of $1.9 million as of December 31, 2019 , and an asset of $ 3.6 million and a liability of $ 9.3 million as of December 31, 2018 . NW Natural is exposed to derivative credit and liquidity risk primarily through securing fixed price natural gas commodity swaps with financial counterparties. NW Natural utilizes master netting arrangements through International Swaps and Derivatives Association contracts to minimize this risk along with collateral support agreements with counterparties based on their credit ratings. In certain cases, NW Natural requires guarantees or letters of credit from counterparties to meet its minimum credit requirement standards. NW Natural's financial derivatives policy requires counterparties to have an investment-grade credit rating at the time the derivative instrument is entered into, and specifies limits on the contract amount and duration based on each counterparty’s credit rating. NW Natural does not speculate with derivatives. Derivatives are used to hedge exposure above risk tolerance limits. Increases in market risk created by the use of derivatives is offset by the exposures they modify. We actively monitor NW Natural's derivative credit exposure and place counterparties on hold for trading purposes or require other forms of credit assurance, such as letters of credit, cash collateral, or guarantees as circumstances warrant. The ongoing assessment of counterparty credit risk includes consideration of credit ratings, credit default swap spreads, bond market credit spreads, financial condition, government actions, and market news. A Monte Carlo simulation model is used to estimate the change in credit and liquidity risk from the volatility of natural gas prices. The results of the model are used to establish trading limits. NW Natural's outstanding financial derivatives at December 31, 2019 mature by October 31, 2022 . We could become materially exposed to credit risk with one or more of our counterparties if natural gas prices experience a significant increase. If a counterparty were to become insolvent or fail to perform on its obligations, we could suffer a material loss; however, we would expect such a loss to be eligible for regulatory deferral and rate recovery, subject to a prudence review. All of our existing counterparties currently have investment-grade credit ratings. Fair Value In accordance with fair value accounting, NW natural includes non-performance risk in calculating fair value adjustments. This includes a credit risk adjustment based on the credit spreads of NW Natural counterparties when in an unrealized gain position, or on NW Natural's own credit spread when it is in an unrealized loss position. The inputs in our valuation models include natural gas futures, volatility, credit default swap spreads, and interest rates. Additionally, the assessment of non-performance risk is generally derived from the credit default swap market and from bond market credit spreads. The impact of the credit risk adjustments for all outstanding derivatives was immaterial to the fair value calculation at December 31, 2019 . As of December 31, 2019 and 2018 , the net fair value was an asset of $ 7.5 million and a liability of $ 5.7 million , respectively, using significant other observable, or Level 2, inputs. No Level 3 inputs were used in our derivative valuations, and there were no transfers between Level 1 or Level 2 during the years ended December 31, 2019 and 2018

Commitments and Contigencies

Commitments and Contigencies	12 Months Ended
	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES Gas Purchase and Pipeline Capacity Purchase and Release Commitments NW Natural has signed agreements providing for the reservation of firm pipeline capacity under which it is required to make fixed monthly payments for contracted capacity. The pricing component of the monthly payment is established, subject to change, by U.S. or Canadian regulatory bodies, or is established directly with private counterparties, as applicable. In addition, NW Natural has entered into long-term agreements to release firm pipeline capacity. NW Natural also enters into short-term and long-term gas purchase agreements. The aggregate amounts of these agreements were as follows at December 31, 2019 : In thousands Gas Pipeline Pipeline 2020 $ 86,175 $ 76,897 $ 4,201 2021 2,899 70,638 3,904 2022 — 68,943 3,904 2023 — 68,563 3,904 2024 — 67,052 3,904 Thereafter — 527,148 3,253 Total 89,074 879,241 23,070 Less: Amount representing interest 481 147,613 840 Total at present value $ 88,593 $ 731,628 $ 22,230 Total fixed charges under capacity purchase agreements were $ 82.2 million for 2019 , $82.6 million for 2018 , and $ 85.3 million for 2017 , of which $ 4.3 million , $4.3 million , and $ 4.5 million , respectively, related to capacity releases. In addition, per-unit charges are required to be paid based on the actual quantities shipped under the agreements. In certain take-or-pay purchase commitments, annual deficiencies may be offset by prepayments subject to recovery over a longer term if future purchases exceed the minimum annual requirements. Leases Refer to Note 7 for a discussion of lease commitments and contingencies. Environmental Matters Refer to Note 18 for a discussion of environmental commitments and contingencies.

Environmental Matters

Environmental Matters	12 Months Ended
	Dec. 31, 2019
Environmental Remediation Obligations [Abstract]
Environmental Matters	ENVIRONMENTAL MATTERS NW Natural owns, or previously owned, properties that may require environmental remediation or action. The range of loss for environmental liabilities is estimated based on current remediation technology, enacted laws and regulations, industry experience gained at similar sites, and an assessment of the probable level of involvement and financial condition of other potentially responsible parties (PRPs). When amounts are prudently expended related to site remediation of those sites described herein, NW Natural has recovery mechanisms in place to collect 96.68% of remediation costs allocable to Oregon customers and 3.32% of costs allocable to Washington customers. These sites are subject to the remediation process prescribed by the Environmental Protection Agency (EPA) and the Oregon Department of Environmental Quality (ODEQ). The process begins with a remedial investigation (RI) to determine the nature and extent of contamination and then a risk assessment (RA) to establish whether the contamination at the site poses unacceptable risks to humans and the environment. Next, a feasibility study (FS) or an engineering evaluation/cost analysis (EE/CA) evaluates various remedial alternatives. It is at this point in the process when NW Natural is able to estimate a range of remediation costs and record a reasonable potential remediation liability, or make an adjustment to the existing liability. From this study, the regulatory agency selects a remedy and issues a Record of Decision (ROD). After a ROD is issued, NW Natural would seek to negotiate a consent decree or consent judgment for designing and implementing the remedy. NW Natural would have the ability to further refine estimates of remediation liabilities at that time. Remediation may include treatment of contaminated media such as sediment, soil and groundwater, removal and disposal of media, institutional controls such as legal restrictions on future property use, or natural recovery. Following construction of the remedy, the EPA and ODEQ also have requirements for ongoing maintenance, monitoring and other post-remediation care that may continue for many years. Where appropriate and reasonably known, NW Natural will provide for these costs in the remediation liabilities described below. Due to the numerous uncertainties surrounding the course of environmental remediation and the preliminary nature of several site investigations, in some cases, NW Natural may not be able to reasonably estimate the high end of the range of possible loss. In those cases, the nature of the possible loss has been disclosed, as has the fact that the high end of the range cannot be reasonably estimated where a range of potential loss is available. Unless there is an estimate within the range of possible losses that is more likely than other cost estimates within that range, NW Natural records the liability at the low end of this range. It is likely changes in these estimates and ranges will occur throughout the remediation process for each of these sites due to the continued evaluation and clarification concerning responsibility, the complexity of environmental laws and regulations and the determination by regulators of remediation alternatives. In addition to remediation costs, NW Natural could also be subject to Natural Resource Damages (NRD) claims. NW Natural will assess the likelihood and probability of each claim and recognize a liability if deemed appropriate. Refer to " Other Portland Harbor " below. Environmental Sites The following table summarizes information regarding liabilities related to environmental sites, which are recorded in other current liabilities and other noncurrent liabilities in NW Natural's balance sheet at December 31: Current Liabilities Non-Current Liabilities In thousands 2019 2018 2019 2018 Portland Harbor site: Gasco/Siltronic Sediments $ 11,632 $ 5,117 $ 46,082 $ 44,351 Other Portland Harbor 2,543 2,600 6,920 6,273 Gasco/Siltronic Upland site 14,203 13,983 43,616 44,830 Central Service Center site — 10 — — Front Street site 10,847 11,402 — 3 Oregon Steel Mills — — 179 179 Total $ 39,225 $ 33,112 $ 96,797 $ 95,636 PORTLAND HARBOR SITE. The Portland Harbor is an EPA listed Superfund site that is approximately 10 miles long on the Willamette River and is adjacent to NW Natural's Gasco uplands site. NW Natural is one of over one hundred PRPs to the Superfund site. In January 2017, the EPA issued its Record of Decision, which selects the remedy for the clean-up of the Portland Harbor site (Portland Harbor ROD). The Portland Harbor ROD estimates the present value total cost at approximately $1.05 billion with an accuracy between -30% and +50% of actual costs. NW Natural's potential liability is a portion of the costs of the remedy for the entire Portland Harbor Superfund site. The cost of that remedy is expected to be allocated among more than one hundred PRPs. NW Natural is participating in a non-binding allocation process with the other PRPs in an effort to resolve its potential liability. The Portland Harbor ROD does not provide any additional clarification around allocation of costs among PRPs; accordingly, NW Natural has not modified any of the recorded liabilities at this time as a result of the issuance of the Portland Harbor ROD. NW Natural manages its liability related to the Superfund site as two distinct remediation projects, the Gasco/Siltronic Sediments and Other Portland Harbor projects. Gasco/Siltronic Sediments. In 2009, NW Natural and Siltronic Corporation entered into a separate Administrative Order on Consent with the EPA to evaluate and design specific remedies for sediments adjacent to the Gasco uplands and Siltronic uplands sites. NW Natural submitted a draft EE/CA to the EPA in May 2012 to provide the estimated cost of potential remedial alternatives for this site. In February 2020, NW Natural and the EPA reached an agreement to amend the Administrative Order on Consent to include additional remedial design activities for sediment investigation costs adjacent to the Gasco uplands . At this time, the estimated costs for the various sediment remedy alternatives in the draft EE/CA for the additional studies and design work needed before the cleanup can occur, and for regulatory oversight throughout the cleanup range from $57.7 million to $350 million . NW Natural has recorded a liability of $ 57.7 million for the sediment clean-up, which reflects the low end of the range. At this time, we believe sediments at this site represent the largest portion of NW Natural's liability related to the Portland Harbor site discussed above. Other Portland Harbor. While we believe liabilities associated with the Gasco/Siltronic sediments site represent NW Natural's largest exposure, there are other potential exposures associated with the Portland Harbor ROD, including NRD costs and harborwide remedial design and cleanup costs (including downstream petroleum contamination), for which allocations among the PRPs have not yet been determined. NW Natural and other parties have signed a cooperative agreement with the Portland Harbor Natural Resource Trustee council to participate in a phased NRD assessment to estimate liabilities to support an early restoration-based settlement of NRD claims. One member of this Trustee council, the Yakama Nation, withdrew from the council in 2009, and in 2017, filed suit against NW Natural and 29 other parties seeking remedial costs and NRD assessment costs associated with the Portland Harbor site, set forth in the complaint. The complaint seeks recovery of alleged costs totaling $0.3 million in connection with the selection of a remedial action for the Portland Harbor site as well as declaratory judgment for unspecified future remedial action costs and for costs to assess the injury, loss or destruction of natural resources resulting from the release of hazardous substances at and from the Portland Harbor site. The Yakama Nation has filed two amended complaints addressing certain pleading defects and dismissing the State of Oregon. On the motion of NW Natural and certain other defendants the federal court has stayed the case pending the outcome of the non-binding allocation proceeding discussed above. NW Natural has recorded a liability for NRD claims which is at the low end of the range of the potential liability; the high end of the range cannot be reasonably estimated at this time. The NRD liability is not included in the aforementioned range of costs provided in the Portland Harbor ROD. GASCO UPLANDS SITE. A predecessor of NW Natural, Portland Gas and Coke Company, owned a former gas manufacturing plant that was closed in 1958 (Gasco site) and is adjacent to the Portland Harbor site described above. The Gasco site has been under investigation by NW Natural for environmental contamination under the ODEQ Voluntary Cleanup Program (VCP). It is not included in the range of remedial costs for the Portland Harbor site noted above. The Gasco site is managed in two parts, the uplands portion and the groundwater source control action. NW Natural submitted a revised Remedial Investigation Report for the uplands to ODEQ in May 2007. In March 2015, ODEQ approved Remedial Assessment (RA) for this site, enabling commencement of work on the FS in 2016. NW Natural has recognized a liability for the remediation of the uplands portion of the site which is at the low end of the range of potential liability; the high end of the range cannot be reasonably estimated at this time. In October 2016, ODEQ and NW Natural agreed to amend their VCP agreement to incorporate a portion of the Siltronic property adjacent to the Gasco site formerly owned by Portland Gas & Coke between 1939 and 1960 into the Gasco RA and FS, excluding the uplands for Siltronic. Previously, NW Natural was conducting an investigation of manufactured gas plant constituents on the entire Siltronic uplands for ODEQ. Siltronic will be working with ODEQ directly on environmental impacts to the remainder of its property. In September 2013, NW Natural completed construction of a groundwater source control system, including a water treatment station, at the Gasco site. NW Natural has estimated the cost associated with the ongoing operation of the system and has recognized a liability which is at the low end of the range of potential cost. NW Natural cannot estimate the high end of the range at this time due to the uncertainty associated with the duration of running the water treatment station, which is highly dependent on the remedy determined for both the upland portion as well as the final remedy for Gasco sediment exposure. OTHER SITES. In addition to those sites above, NW Natural has environmental exposures at three other sites: Central Service Center, Front Street and Oregon Steel Mills. NW Natural may have exposure at other sites that have not been identified at this time. Due to the uncertainty of the design of remediation, regulation, timing of the remediation and in the case of the Oregon Steel Mills site, pending litigation, liabilities for each of these sites have been recognized at their respective low end of the range of potential liability; the high end of the range could not be reasonably estimated at this time. Central Service Center site. The investigative phase to characterize the existing site has been completed and determined by the Oregon Department of Environmental Quality (DEQ) to be sufficient to allow for the issuance of a Conditional No Further Action (cNFA). The Company is now conducting ongoing environmental monitoring activities over the next 5 years in order to meet the conditions which were included within the cNFA. Front Street site. The Front Street site was the former location of a gas manufacturing plant NW Natural operated (the former Portland Gas Manufacturing site, or PGM). At ODEQ’s request, NW Natural conducted a sediment and source control investigation and provided findings to ODEQ. In December 2015, an FS on the former Portland Gas Manufacturing site was completed. In July 2017, ODEQ issued the PGM ROD. The ROD specifies the selected remedy, which requires a combination of dredging, capping, treatment, and natural recovery. In addition, the selected remedy also requires institutional controls and long-term inspection and maintenance. NW Natural revised the liability in the second quarter of 2017 to incorporate the estimated undiscounted cost of approximately $10.5 million for the selected remedy. Further, NW Natural has recognized an additional liability of $0.3 million for additional studies and design costs as well as regulatory oversight throughout the cleanup. NW Natural plans to construct the remedy in 2020. Oregon Steel Mills site. Refer to the “Legal Proceedings,” below. Environmental Cost Deferral and Recovery NW Natural has authorizations in Oregon and Washington to defer costs related to remediation of properties that are owned or were previously owned by NW Natural. In Oregon, a Site Remediation and Recovery Mechanism (SRRM) is currently in place to recover prudently incurred costs allocable to Oregon customers, subject to an earnings test. On October 21, 2019 the WUTC authorized an Environmental Cost Recovery Mechanism (ECRM) for recovery of prudently incurred costs allocable to Washington customers beginning November 1, 2019. The following table presents information regarding the total regulatory assets deferred as of December 31: In thousands 2019 2018 Deferred costs and interest (1) $ 36,673 $ 41,883 Accrued site liabilities (2) 135,662 128,369 Insurance proceeds and interest (79,949 ) (88,502 ) Total regulatory asset deferral (1) $ 92,386 $ 81,750 Current regulatory assets (3) 4,762 5,601 Long-term regulatory assets (3) 87,624 76,149 (1) Includes pre-review and post-review deferred costs, amounts currently in amortization, and interest, net of amounts collected from customers. In Oregon, NW Natural earns a carrying charge on cash amounts paid, whereas amounts accrued but not yet paid do not earn a carrying charge until expended. NW Natural also accrues a carrying charge on insurance proceeds for amounts owed to customers. In Washington, neither the cash paid nor insurance proceeds accrue a carrying charge. (2) Excludes 3.32% of the Front Street site liability, or $0.4 million in 2019 and $0.4 million in 2018 , as the OPUC only allows recovery of 96.68% of costs for those sites allocable to Oregon, including those that historically served only Oregon customers. (3) Amounts included in this estimate are still subject to a prudence review by the OPUC and WUTC, and earnings test review by the OPUC. Amounts do not include the $5.0 million tariff rider. See " Oregon SRRM " below. Oregon SRRM COLLECTIONS FROM OREGON CUSTOMERS. Under the SRRM collection process there are three types of deferred environmental remediation expense: • Pre-review - This class of costs represents remediation spend that has not yet been deemed prudent by the OPUC. Carrying costs on these remediation expenses are recorded at NW Natural's authorized cost of capital. NW Natural anticipates the prudence review for annual costs and approval of the earnings test prescribed by the OPUC to occur by the third quarter of the following year. • Post-review - This class of costs represents remediation spend that has been deemed prudent and allowed after applying the earnings test, but is not yet included in amortization. NW Natural earns a carrying cost on these amounts at a rate equal to the five-year treasury rate plus 100 basis points. • Amortization - This class of costs represents amounts included in current customer rates for collection and is generally calculated as one-fifth of the post-review deferred balance. NW Natural earns a carrying cost equal to the amortization rate determined annually by the OPUC, which approximates a short-term borrowing rate. In addition to the collection amount noted above, an order issued by the OPUC provides for the annual collection of $5.0 million from Oregon customers through a tariff rider. As NW Natural collects amounts from customers, it recognizes these collections as revenue and separately amortizes an equal and offsetting amount of its deferred regulatory asset balance through the environmental remediation operating expense line shown separately in the operating expense section of the income statement. NW Natural received total environmental insurance proceeds of approximately $150 million as a result of settlements from litigation that was dismissed in July 2014. Under a 2015 OPUC order which established the SRRM, one-third of the Oregon allocated proceeds were applied to costs deferred through 2012 with the remaining two-thirds applied to costs at a rate of $5.0 million per year plus interest over the following 20 years. NW Natural accrues interest on the Oregon allocated insurance proceeds in the customer’s favor at a rate equal to the five-year treasury rate plus 100 basis points. As of December 31, 2019 , NW Natural has applied $78.2 million of insurance proceeds to prudently incurred remediation costs allocated to Oregon. OREGON ENVIRONMENTAL EARNINGS TEST. To the extent NW Natural earns at or below its authorized Return on Equity (ROE), remediation expenses and interest in excess of the $5.0 million tariff rider and $5.0 million insurance proceeds are recoverable through the SRRM. To the extent NW Natural earns more than its authorized ROE in a year, it is required to cover environmental expenses and interest on expenses greater than the $10.0 million with those earnings that exceed its authorized ROE. Washington ECRM WASHINGTON DEFERRAL. On October 21, 2019 the WUTC issued an order (WUTC Order) establishing the ECRM which allows for recovery of past deferred and future prudently incurred environmental remediation costs allocable to Washington customers through application of insurance proceeds and collections from customers. Environmental remediation expenses relating to sites that previously served both Oregon and Washington customers are allocated between states with Washington customers receiving 3.32% percent of the costs and insurance proceeds. As a result of the WUTC Order, in the fourth quarter of 2019 approximately $3.0 million of prudently incurred costs deferred from the initial deferral authorization in February 2011 through November 2018 were fully offset with insurance proceeds. In addition, approximately $1.5 million of disallowed deferred environmental remediation expenses incurred prior to the deferral authorization were charged to environmental remediation expense. Insurance proceeds will be fully applied to costs incurred between December 2018 and June 2019 once deemed prudent in future rate proceedings. Remaining insurance proceeds will be amortized over a 10.5 year period ending December 31, 2029. On an annual basis, NW Natural will file for a prudence determination and a request to amortize costs to the extent that remediation expenses exceed the insurance amortization. After insurance proceeds are fully amortized, if in a particular year the request to collect deferred amounts exceeds one percent of Washington normalized revenues, then the excess will be collected over three years with interest. Legal Proceedings NW Holdings is not currently party to any direct claims or litigation, though in the future it may be subject to claims and litigation arising in the ordinary course of business. NW Natural is subject to claims and litigation arising in the ordinary course of business. Although the final outcome of any of these legal proceedings cannot be predicted with certainty, including the matter described below, NW Natural and NW Holdings do not expect that the ultimate disposition of any of these matters will have a material effect on financial condition, results of operations, or cash flows. OREGON STEEL MILLS SITE. In 2004, NW Natural was served with a third-party complaint by the Port of Portland (the Port) in a Multnomah County Circuit Court case, Oregon Steel Mills, Inc. v. The Port of Portland. The Port alleges that in the 1940s and 1950s petroleum wastes generated by NW Natural's predecessor, Portland Gas & Coke Company, and 10 other third-party defendants, were disposed of in a waste oil disposal facility operated by the United States or Shaver Transportation Company on property then owned by the Port and now owned by Evraz Oregon Steel Mills. The complaint seeks contribution for unspecified past remedial action costs incurred by the Port regarding the former waste oil disposal facility as well as a declaratory judgment allocating liability for future remedial action costs. No date has been set for trial. In August 2017, the case was stayed pending the outcome of the Portland Harbor allocation process or other mediation. Although the final outcome of this proceeding cannot be predicted with certainty, NW Natural and NW Holdings do not expect the ultimate disposition of this matter will have a material effect on NW Natural's or NW Holdings' financial condition, results of operations, or cash flows. For additional information regarding other commitments and contingencies, see Note 17 .

Discontinued Operations

Discontinued Operations	12 Months Ended
	Dec. 31, 2019
Northwest Natural Gas Company [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operations	DISCONTINUED OPERATIONS NW Holdings On June 20, 2018, NWN Gas Storage, then a wholly-owned subsidiary of NW Natural, entered into a Purchase and Sale Agreement (the Agreement) that provides for the sale by NWN Gas Storage of all of the membership interests in Gill Ranch. Gill Ranch owns a 75% interest in the natural gas storage facility located near Fresno, California known as the Gill Ranch Gas Storage Facility. Pacific Gas and Electric Company (PG&E) owns the remaining 25% interest in the Gill Ranch Gas Storage Facility. The CPUC regulates Gill Ranch under a market-based rate model which allows for the price of storage services to be set by the marketplace. The CPUC also regulates the issuance of securities, system of accounts, and regulates intrastate storage services. The sale of Gill Ranch was approved by the CPUC in December 2019. The Agreement provides for an initial cash purchase price of $25.0 million (subject to a working capital adjustment), plus potential additional payments to NWN Gas Storage of up to $26.5 million in the aggregate if Gill Ranch achieves certain economic performance levels for the first three full gas storage years (April 1 of one year through March 31 of the following year) occurring after the closing and the remaining portion of the gas storage year during which the closing occurs. As a result of the strategic shift away from the California gas storage market and the significance of Gill Ranch's financial results in 2017, we concluded that the pending sale of Gill Ranch qualified it as assets and liabilities held for sale and discontinued operations. As such, the assets and liabilities associated with Gill Ranch have been classified as discontinued operations assets and discontinued operations liabilities, respectively, and, the results of Gill Ranch are presented, net of tax, as discontinued operations separately from the results of continuing operations for all periods presented. The expenses included in the results of discontinued operations are the direct operating expenses incurred by Gill Ranch that may be reasonably segregated from the costs of NW Holdings' continuing operations. The following table presents the carrying amounts of the major components of Gill Ranch that are classified as discontinued operations assets and liabilities on the consolidated balance sheets: NW Holdings Discontinued Operations In thousands 2019 2018 Assets: Accounts receivable $ 333 $ 390 Inventories 695 685 Other current assets 457 333 Property, plant, and equipment 13,291 11,621 Less: Accumulated depreciation 7 7 Operating lease right of use asset 118 — Other non-current assets 247 247 Total discontinued operations assets - current assets (1) $ 15,134 $ 13,269 Liabilities: Accounts payable $ 1,250 $ 873 Other current liabilities 848 307 Operating lease liabilities 116 — Other non-current liabilities 11,495 11,779 Total discontinued operations liabilities - current liabilities (1) $ 13,709 $ 12,959 (1) The total assets and liabilities of Gill Ranch are classified as current as of December 31, 2018 because it was probable that the sale would be completed within one year. The following table presents the operating results of Gill Ranch, which was historically reported within the gas storage segment, and is presented net of tax on NW Holdings' consolidated statements of comprehensive income: NW Holdings Discontinued Operations In thousands, except per share data 2019 2018 2017 Revenues $ 5,301 $ 3,579 $ 7,135 Expenses Operations and maintenance 8,587 5,771 7,245 General taxes 219 479 1,373 Depreciation and amortization 423 430 4,525 Other expenses and interest 931 609 975 Impairment expense — — 192,478 Total expenses 10,160 7,289 206,596 Loss from discontinued operations before income tax (4,859 ) (3,710 ) (199,461 ) Income tax benefit (1) (1,283 ) (968 ) (71,765 ) Loss from discontinued operations, net of tax $ (3,576 ) $ (2,742 ) $ (127,696 ) Loss from discontinued operations per share of common stock: Basic $ (0.12 ) $ (0.10 ) $ (4.45 ) Diluted (0.12 ) (0.09 ) (4.44 ) (1) 2017 income tax benefit includes approximately $18 million of tax benefit from the enactment of the TCJA. The TCJA was enacted December 22, 2017 and resulted in the federal tax rate changing from 35% to 21% . NW Natural As part of the holding company reorganization in October 2018, NWN Energy, NWN Gas Storage, Gill Ranch, NNG Financial, NWN Water, and NW Holdings, which were direct and indirect subsidiaries of NW Natural prior to the reorganization, are no longer subsidiaries of NW Natural. See Note 1 for additional information. As a result, NW Natural's financial statements reflect amounts related to these entities as discontinued operations for all periods presented. The expenses included in the results of discontinued operations are the direct operating expenses incurred by the entities that may be reasonably segregated from the costs of NW Natural's continuing operations. The following table presents the operating results prior to the holding company reorganization effective October 1, 2018 of NWN Energy, NWN Gas Storage, Gill Ranch, NNG Financial, NWN Water, and NW Holdings, which were historically reported within the gas storage segment and other, and is presented net of tax on NW Natural's consolidated statements of comprehensive income: NW Natural Discontinued Operations In thousands, except per share data 2018 2017 Revenues $ 3,016 $ 7,360 Expenses Operations and maintenance 4,151 7,423 General taxes 448 1,410 Depreciation and amortization 420 4,555 Other expenses and interest 342 650 Impairment expense — 192,478 Total expenses 5,361 206,516 Loss from discontinued operations before income tax (2,345 ) (199,156 ) Income tax benefit (1) (622 ) (71,813 ) Loss from discontinued operations, net of tax $ (1,723 ) $ (127,343 ) (1) 2017 income tax benefit includes approximately $18 million of tax benefit from the enactment of the TCJA. The TCJA was enacted December 22, 2017 and resulted in the federal tax rate changing from 35% to 21% .

Subsequent Event

Subsequent Event	12 Months Ended
	Dec. 31, 2019
Subsequent Event [Line Items]
Subsequent Events [Text Block]	Subsequent Events Suncadia Acquisition Completed On January 31, 2020, NWN Water of Washington, a wholly-owned indirect subsidiary of NW Holdings, completed the acquisition of Suncadia Water, a privately-owned water utility, and Suncadia Environmental, a wastewater company (collectively referred to as Suncadia). The acquisition was made for preliminary cash consideration of $18.9 million , subject to closing adjustments. Suncadia is based in Cle Elum, Washington and serves approximately 2,800 connections. A $1.0 million letter of credit outstanding at NW Holdings as of December 31, 2019 for purposes of facilitating the acquisition was extinguished upon the close of the transaction. The preliminary allocation of consideration to the acquired assets and assumed liabilities based on their fair value is not yet complete as valuation procedures are pending. We expect the purchase price to be primarily allocated to property, plant and equipment and goodwill. Acquisition costs were insignificant and were expensed as incurred. See Note 2 and Note 15 for more information regarding business combinations.

Quarterly Financial Information

Quarterly Financial Information	12 Months Ended
	Dec. 31, 2019
Schedule Of Quarterly Financial Information [Abstract]
Quarterly Financial Information [Text Block]	NORTHWEST NATURAL HOLDING COMPANY QUARTERLY FINANCIAL INFORMATION (UNAUDITED) NW Holdings Quarter Ended (1) In thousands, except per share data March 31 June 30 September 30 December 31 2019 Operating revenues $ 285,348 $ 123,433 $ 90,317 $ 247,274 Net income (loss) from continuing operations 43,418 2,051 (18,506 ) 38,348 Loss from discontinued operations, net of tax (217 ) (956 ) (795 ) (1,608 ) Net income (loss) $ 43,201 $ 1,095 $ (19,301 ) $ 36,740 Average common shares outstanding: Basic 28,906 29,337 30,429 30,448 Diluted 28,970 29,394 30,429 30,521 Earnings (loss) from continuing operations per share of common stock: Basic $ 1.50 $ 0.07 $ (0.61 ) $ 1.26 Diluted 1.50 0.07 (0.61 ) 1.26 Loss from discontinued operations per share of common stock: Basic $ (0.01 ) $ (0.03 ) $ (0.02 ) $ (0.05 ) Diluted (0.01 ) (0.03 ) (0.02 ) (0.05 ) Earnings (loss) per share of common stock: Basic $ 1.49 $ 0.04 $ (0.63 ) $ 1.21 Diluted 1.49 0.04 (0.63 ) 1.20 2018 Operating revenues $ 263,635 $ 124,567 $ 91,239 $ 226,702 Net income (loss) from continuing operations 42,011 (339 ) (11,144 ) 36,783 Loss from discontinued operations, net of tax (474 ) (659 ) (650 ) (959 ) Net income (loss) $ 41,537 $ (998 ) $ (11,794 ) $ 35,824 Average common shares outstanding: Basic 28,753 28,791 28,815 28,851 Diluted 28,803 28,791 28,815 28,940 Earnings (loss) from continuing operations per share of common stock: Basic $ 1.46 $ (0.01 ) $ (0.39 ) $ 1.27 Diluted 1.46 (0.01 ) (0.39 ) 1.27 Loss from discontinued operations per share of common stock: Basic $ (0.02 ) $ (0.02 ) $ (0.02 ) $ (0.03 ) Diluted (0.02 ) (0.02 ) (0.02 ) (0.03 ) Earnings (loss) per share of common stock: Basic $ 1.44 $ (0.03 ) $ (0.41 ) $ 1.24 Diluted 1.44 (0.03 ) (0.41 ) 1.24 (1) Quarterly earnings (loss) per share are based upon the average number of common shares outstanding during each quarter. Variations in earnings between quarterly periods are due primarily to the seasonal nature of our business. NORTHWEST NATURAL GAS COMPANY QUARTERLY FINANCIAL INFORMATION (UNAUDITED) NW Natural Quarter ended In thousands March 31 June 30 September 30 December 31 2019 Operating revenues $ 284,846 $ 122,242 $ 87,592 $ 245,264 Net income (loss) $ 43,895 $ 3,054 $ (17,588 ) $ 39,613 2018 Operating revenues $ 263,635 $ 124,563 $ 91,227 $ 226,146 Net income (loss) from continuing operations 42,014 (271 ) (11,275 ) 37,581 Loss from discontinued operations, net of tax (477 ) (727 ) (519 ) — Net income (loss) $ 41,537 $ (998 ) $ (11,794 ) $ 37,581

Condensed Financials Standalone

Condensed Financials Standalone Holdco Condensed Financials Standalone Holdco (Notes)	12 Months Ended
	Dec. 31, 2019
Condensed Financial Statements, Captions [Line Items]
Condensed Financial Information of Parent Company Only Disclosure [Text Block]	NORTHWEST NATURAL HOLDING COMPANY CONDENSED STATEMENTS OF COMPREHENSIVE INCOME (PARENT COMPANY ONLY) In thousands Year ended December 31, 2019 Inception through December 31, 2018 Operating expenses: Operations and maintenance $ 2,747 $ 838 Total operating expenses 2,747 838 Loss from operations (2,747 ) (838 ) Earnings from investment in subsidiaries, net of tax 64,328 36,469 Other income (expense), net (22 ) 36 Interest expense, net 726 53 Income before income taxes 60,833 35,614 Income tax expense (benefit) (902 ) (225 ) Net income $ 61,735 $ 35,839 See Notes to Condensed Financial Statements NORTHWEST NATURAL HOLDING COMPANY CONDENSED BALANCE SHEETS (PARENT COMPANY ONLY) As of December 31, In thousands 2019 2018 Assets: Current assets: Cash and cash equivalents $ 119 4,011 Receivables from affiliates 1,950 2,796 Income taxes receivable 256 6,000 Other current assets 4,600 3,078 Total current assets 6,925 15,885 Non-current assets: Investments in subsidiaries 888,477 754,971 Other investments 24 65 Deferred tax assets 191 — Other non-current assets 245 310 Total non-current assets 888,937 755,346 Total assets $ 895,862 $ 771,231 Liabilities and equity: Current liabilities: Short-term debt $ 24,000 $ — Accounts payable 612 168 Payables to affiliates 3,697 9,166 Taxes accrued 127 — Interest accrued — 32 Other current liabilities 37 — Total current liabilities 28,473 9,366 Long-term debt — (1 ) Deferred credits and other non-current liabilities: Deferred tax liabilities — 7 Total deferred credits and other non-current liabilities — 7 Equity: Common stock 840,364 739,722 Retained earnings 27,025 22,137 Total equity 867,389 761,859 Total liabilities and equity $ 895,862 $ 771,231 See Notes to Condensed Financial Statements NORTHWEST NATURAL HOLDING COMPANY CONDENSED STATEMENTS OF CASH FLOWS (PARENT COMPANY ONLY) In thousands Year ended December 31, 2019 Inception through December 31, 2018 Operating activities: Net income $ 61,735 $ 35,839 Adjustments to reconcile net income to cash used in operations: Equity in earnings of subsidiaries, net of tax (64,328 ) (36,469 ) Deferred income taxes (198 ) 7 Other 66 15 Changes in assets and liabilities: Receivables, net 846 (585 ) Income and other taxes 4,325 (9,034 ) Accounts payable (5,177 ) 9,304 Interest accrued (32 ) 32 Other, net (346 ) (44 ) Cash used in operating activities (3,109 ) (935 ) Investing activities: Contributions to subsidiaries (157,591 ) (1,804 ) Cash used in investing activities (157,591 ) (1,804 ) Financing activities: Proceeds from stock options exercised 2,015 — Proceeds from common stock issued 92,956 — Change in short-term debt 24,000 — Cash dividend payments received from subsidiaries 88,439 — Cash dividend payments on common stock (53,339 ) (12,923 ) Capital contributions — 20,000 Other 2,737 (327 ) Cash provided by financing activities 156,808 6,750 Increase (decrease) in cash and cash equivalents (3,892 ) 4,011 Cash and cash equivalents, beginning of period 4,011 — Cash and cash equivalents, end of period $ 119 $ 4,011 See Notes to Condensed Financial Statements NW Holdings is an energy services holding company that conducts substantially all of its business operations through its subsidiaries, particularly NW Natural. These condensed financial statements and related footnotes have been prepared in accordance with Rule 12-04, Schedule I of Regulation S-X. These financial statements, in which NW Holdings' subsidiaries have been included using the equity method, should be read in conjunction with the consolidated financial statements and notes thereto of NW Holdings included in Item 8 of this Form 10-K. Equity earnings of subsidiaries including earnings from NW Natural were $64.3 million and $35.6 million for the years ended December 31, 2019 and 2018 . Cash dividends paid to NW Holdings from wholly-owned subsidiaries were $88.4 million for the year ended December 31, 2019 . No cash dividends were paid from subsidiaries to NW Holdings in 2018 . 2. DEBT For information concerning NW Holdings' debt obligations, see Note 9 to the consolidated financial statements included in Item 8 of this report.

Valuation Allowances and Reserv

Valuation Allowances and Reserves	12 Months Ended
	Dec. 31, 2019
Entity Information [Line Items]
Schedule of Valuation and Qualifying Accounts	NORTHWEST NATURAL HOLDING COMPANY SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES COLUMN A COLUMN B COLUMN C COLUMN D COLUMN E Additions Deductions In thousands (year ended December 31) Balance at beginning of period Charged to costs and expenses Charged to other accounts Net write-offs Balance at end of period 2019 Reserves deducted in balance sheet from assets to which they apply: Allowance for uncollectible accounts $ 977 $ 450 $ — $ 754 $ 673 2018 Reserves deducted in balance sheet from assets to which they apply: Allowance for uncollectible accounts $ 956 $ 680 $ — $ 659 $ 977 2017 Reserves deducted in balance sheet from assets to which they apply: Allowance for uncollectible accounts $ 1,290 $ 865 $ — $ 1,199 $ 956 NORTHWEST NATURAL GAS COMPANY SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES COLUMN A COLUMN B COLUMN C COLUMN D COLUMN E Additions Deductions In thousands (year ended December 31) Balance at beginning of period Charged to costs and expenses Charged to other accounts Net write-offs Balance at end of period 2019 Reserves deducted in balance sheet from assets to which they apply: Allowance for uncollectible accounts $ 975 $ 450 $ — $ 753 $ 672 2018 Reserves deducted in balance sheet from assets to which they apply: Allowance for uncollectible accounts $ 956 $ 678 $ — $ 659 $ 975 2017 Reserves deducted in balance sheet from assets to which they apply: Allowance for uncollectible accounts $ 1,290 $ 865 $ — $ 1,199 $ 956

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with generally accepted accounting principles in the United States of America (U.S. GAAP) requires management to make estimates and assumptions that affect reported amounts in the consolidated financial statements and accompanying notes. Actual amounts could differ from those estimates, and changes would most likely be reported in future periods. Management believes the estimates and assumptions used are reasonable .
Industry Regulation	Industry Regulation NW Holdings' principal business is to operate as a holding company for NW Natural and its other subsidiaries. NW Natural's principal business is the distribution of natural gas, which is regulated by the OPUC and WUTC. NW Natural also has natural gas storage services, which are regulated by the FERC, and to a certain extent by the OPUC and WUTC. Additionally, certain of NW Holdings' subsidiaries own water businesses, which are regulated by the public utility commission in the state in which the water utility is located, which is currently Oregon, Washington and Idaho. Accounting records and practices of the regulated businesses conform to the requirements and uniform system of accounts prescribed by these regulatory authorities in accordance with U.S. GAAP. The businesses in which customer rates are regulated by the OPUC, WUTC, IPUC, and FERC have approved cost-based rates which are intended to allow such businesses to earn a reasonable return on invested capital. In applying regulatory accounting principles, NW Holdings and NW Natural capitalize or defer certain costs and revenues as regulatory assets and liabilities pursuant to orders of the applicable state public utility commission, which provide for the recovery of revenues or expenses from, or refunds to, utility customers in future periods, including a return or a carrying charge in certain cases. Amounts NW Natural deferred as regulatory assets and liabilities were as follows: Regulatory Assets In thousands 2019 2018 Current: Unrealized loss on derivatives (1) $ 2,000 $ 12,381 Gas costs 20,140 2,873 Environmental costs (2) 4,762 5,601 Decoupling (3) 1,969 9,140 Pension balancing (4) 5,939 — Income taxes 2,209 2,218 Other (5) 4,910 9,717 Total current $ 41,929 $ 41,930 Non-current: Unrealized loss on derivatives (1) $ 609 $ 3,025 Pension balancing (4) 48,251 74,173 Income taxes 17,173 19,185 Pension and other postretirement benefit liabilities 173,262 174,993 Environmental costs (2) 87,624 76,149 Gas costs 2,866 9,978 Decoupling (3) — 2,545 Other (5) 13,361 11,738 Total non-current $ 343,146 $ 371,786 Regulatory Liabilities In thousands 2019 2018 Current: Gas costs $ 1,223 $ 17,182 Unrealized gain on derivatives (1) 6,622 8,740 Decoupling (3) 4,831 2,264 Income taxes (6) 8,435 — Other (5) 23,546 19,250 Total current $ 44,657 $ 47,436 Non-current: Gas costs $ 2,013 $ 552 Unrealized gain on derivatives (1) 3,337 725 Decoupling (3) 6,378 — Income taxes (6) 198,219 225,408 Accrued asset removal costs (7) 401,893 380,464 Other (5) 13,877 4,411 Total non-current $ 625,717 $ 611,560 (1) Unrealized gains or losses on derivatives are non-cash items and, therefore, do not earn a rate of return or a carrying charge. These amounts are recoverable through natural gas distribution rates as part of the annual Purchased Gas Adjustment (PGA) mechanism when realized at settlement. (2) Refer to the Environmental Cost Deferral and Recovery table in Note 18 for a description of environmental costs. (3) This deferral represents the margin adjustment resulting from differences between actual and expected volumes. (4) Refer to Note 10 for information regarding the deferral of pension expenses. (5) Balances consist of deferrals and amortizations under approved regulatory mechanisms and typically earn a rate of return or carrying charge. (6) This balance represents estimated amounts associated with the Tax Cuts and Jobs Act. See Note 11 . (7) Estimated costs of removal on certain regulated properties are collected through rates. See "Accounting Policies— Plant, Property, and Accrued Asset Removal Costs " below. The amortization period for NW Natural's regulatory assets and liabilities ranges from less than one year to an indeterminable period. Regulatory deferrals for gas costs payable are generally amortized over 12 months beginning each November 1 following the gas contract year during which the deferred gas costs are recorded. Similarly, most other regulatory deferred accounts are amortized over 12 months . However, certain regulatory account balances, such as income taxes, environmental costs, pension liabilities, and accrued asset removal costs, are large and tend to be amortized over longer periods once NW Natural has agreed upon an amortization period with the respective regulatory agency. We believe all costs incurred and deferred at December 31, 2019 are prudent. All regulatory assets and liabilities are reviewed annually for recoverability, or more often if circumstances warrant. If we should determine that all or a portion of these regulatory assets or liabilities no longer meet the criteria for continued application of regulatory accounting, then NW Natural would be required to write-off the net unrecoverable balances in the period such determination is made. Regulatory interest income of $19.6 million and $7.6 million and regulatory interest expense of $12.3 million and $5.9 million was recognized within other income (expense), net for the years ended December 31, 2019 and 2018 , respectively. Environmental Regulatory Accounting See Note 18 for information about the SRRM and OPUC orders regarding implementation.
New Accounting Standards	New Accounting Standards NW Natural and NW Holdings consider the applicability and impact of all accounting standards updates (ASUs) issued by the Financial Accounting Standards Board (FASB). ASUs not listed below were assessed and determined to be either not applicable or are expected to have minimal impact on consolidated financial position or results of operations. Recently Adopted Accounting Pronouncements ACCUMULATED OTHER COMPREHENSIVE INCOME. On February 14, 2018, the FASB issued ASU 2018-02, "Income Statement—Reporting Comprehensive Income: Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income." This update was issued in response to concerns from certain stakeholders regarding the current requirements under U.S. GAAP that deferred tax assets and liabilities are adjusted for a change in tax laws or rates, and the effect is to be included in income from continuing operations in the period of the enactment date. This requirement is also applicable to items in accumulated other comprehensive income where the related tax effects were originally recognized in other comprehensive income. The adjustment of deferred taxes due to the new corporate income tax rate enacted through the Tax Cuts and Jobs Act (TCJA) on December 22, 2017 recognized in income from continuing operations causes the tax effects of items within accumulated other comprehensive income (referred to as stranded tax effects) to not reflect the appropriate tax rate. The amendments in this update allow but do not require a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the TCJA and require certain disclosures about stranded tax effects. NW Natural adopted and applied the standard in the first quarter of 2019. NW Natural elected to reclassify the stranded tax effects of the TCJA of $1.4 million from accumulated other comprehensive loss to retained earnings in the period of adoption. Going forward, our policy is that, in the event that regulation changes result in stranded tax effects, such amounts will be reclassified from accumulated other comprehensive income (loss) to retained earnings in the final period that the related deferred tax balance remeasurement is expected to impact income from continuing operations. DERIVATIVES AND HEDGING. On August 28, 2017, the FASB issued ASU 2017-12, "Derivatives and Hedging: Targeted Improvements to Accounting for Hedging Activities." The purpose of the amendment is to more closely align hedge accounting with companies’ risk management strategies. The ASU amends the accounting for risk component hedging, the hedged item in fair value hedges of interest rate risk, and amounts excluded from the assessment of hedge effectiveness. The guidance also amends the recognition and presentation of the effect of hedging instruments and includes other simplifications of hedge accounting. The amendments in this update were effective beginning January 1, 2019 and were applied prospectively to hedging instruments. The adoption did not have an impact on the financial statements or disclosures of NW Holdings or NW Natural. GOODWILL. On January 26, 2017, the FASB issued ASU 2017-04, "Simplifying the Test for Goodwill Impairment." The ASU removes Step 2 from the goodwill impairment test and under the amended guidance an entity should perform its annual goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount and recognize an impairment charge for the amount in which the carrying amounts exceed the fair value of the reporting unit. The amendments in this standard are effective for us beginning January 1, 2020 and early adoption is permitted for interim or annual goodwill impairment tests performed after January 1, 2017. NW Natural early adopted ASU 2017-04 in the quarter ended September 30, 2018. The adoption of this ASU did not materially affect the financial statements and disclosures of NW Holdings or NW Natural. LEASES. On February 25, 2016, the FASB issued ASU 2016-02, "Leases," which revises the existing lease accounting guidance. Pursuant to the new standard (“ASC 842”), lessees are required to recognize all leases, including operating leases that are greater than 12 months at lease commencement, on the balance sheet and record corresponding right of use assets and lease liabilities. Lessor accounting will remain substantially the same under the new standard. Quantitative and qualitative disclosures are also required for users of the financial statements to have a clear understanding of the nature of our leasing activities. We elected the alternative prospective transition approach for adoption beginning January 1, 2019. All comparative periods prior to January 1, 2019 will retain the financial reporting and disclosure requirements of ASC 840 “Leases” (“ASC 840”). There was no cumulative effect adjustment to the opening balance of retained earnings recorded as of January 1, 2019 for adoption as there were no initial direct costs or other capitalized costs related to the legacy leases that needed to be derecognized upon adoption of ASC 842. We elected the land easement optional practical expedient to not evaluate existing or expired land easements that were not previously accounted for as leases under the ASC 840 lease guidance. For the existing lease portfolio, we did not elect the optional practical expedient package to retain the legacy lease accounting conclusions upon adoption; we re-assessed our existing contracts under the new leasing standard including whether the contract meets the definition of a lease and lease classification. As a result, we determined that most of our underground gas storage contracts no longer meet the definition of a lease under the new lease standard. In October 2017, NW Natural entered into a 20-year operating lease agreement commencing in 2020 for a new corporate operations center location in Portland, Oregon. The lease was analyzed under ASC 840 in consideration of build-to-suit lease accounting guidance with the conclusion that NW Natural was the owner of the asset during construction for accounting purposes. Under the new lease standard, ASC 842, NW Natural is no longer considered the owner of the asset during construction for accounting purposes. As such, in January 2019 we derecognized the build-to-suit asset and liability balances of $26.0 million as of December 31, 2018 that were previously recorded within property, plant and equipment and other non-current liabilities in the consolidated balance sheet. Upon adoption on January 1, 2019, NW Holdings recorded an operating lease right of use asset and an associated operating lease liability of approximately $7.3 million , of which $7.0 million was recorded at NW Natural. Lease liabilities are measured using NW Natural's incremental borrowing rate based on information available at the lease commencement date in determining the present value of lease payments. As of December 31, 2019 , our lessee portfolio under the new standard consists primarily of our current leased corporate operations center, which expires in 2020. Our lessor portfolio primarily consists of our North Mist Facility which classified as a sales-type lease. See Note 7 for more information. CLOUD COMPUTING. On August 29, 2018, the FASB issued ASU 2018-15, "Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract." The purpose of the amendment is to align the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. The amendments in this update are effective for us beginning January 1, 2020. Early adoption is permitted, and NW Holdings and NW Natural early adopted ASU 2018-15 in the quarter ended March 31, 2019 utilizing the prospective application methodology. The adoption of this ASU did not materially affect the financial statements and disclosures of NW Holdings or NW Natural. Recently Issued Accounting Pronouncements INCOME TAXES. On December 18, 2019, the FASB issued ASU 2019-12, "Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes." The purpose of the amendment is to reduce cost and complexity related to accounting for income taxes by removing certain exceptions to the general principles and improving consistent application for other areas in Topic 740. The amendments in this update are effective for us beginning January 1, 2021. Early adoption is permitted. The amended presentation and disclosure guidance should be applied retrospectively. We do not expect this ASU to materially affect the financial statements and disclosures of NW Holdings or NW Natural. RETIREMENT BENEFITS. On August 28, 2018, the FASB issued ASU 2018-14, "Changes to the Disclosure Requirements for Defined Benefit Plans." The purpose of the amendment is to modify the disclosure requirements for defined benefit pension and other postretirement plans. The amendments in this update are effective for us beginning January 1, 2020. Early adoption is permitted. The amended presentation and disclosure guidance should be applied retrospectively. We do not expect this ASU to materially affect the financial statements and disclosures of NW Holdings or NW Natural. FAIR VALUE MEASUREMENT. On August 28, 2018, the FASB issued ASU 2018-13, "Changes to the Disclosure Requirements for Fair Value Measurement." The purpose of the amendment is to modify the disclosure requirements for fair value measurements. The amendments in this update are effective for us beginning January 1, 2020. Early adoption is permitted. The amendments on changes in unrealized gains and losses, the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements and the narrative description of measurement uncertainty should be applied prospectively. All other amendments should be applied retrospectively. NW Holdings and NW Natural do not have either Level 3 fair value measurements or transfers between Level 1 or Level 2 in their current portfolios, and therefore, we do not expect this ASU to have an impact on the financial statements and disclosures of NW Holdings or NW Natural. CREDIT LOSSES. On June 16, 2016, the FASB issued ASU 2016-13, "Measurement of Credit Losses on Financial Instruments," which applies to financial assets subject to credit losses and measured at amortized cost. The new standard will require financial assets measured at amortized cost to be presented at the net amount expected to be collected and the allowance for credit losses is to be recorded as a valuation account that is deducted from the amortized cost basis. The amendments in this update are effective beginning January 1, 2020. Early adoption is permitted for fiscal years beginning after December 15, 2018. The majority of NW Holdings' and NW Natural's financial assets are short-term in nature, such as trade receivables, and therefore, we do not expect this ASU to materially affect our financial statements and disclosures.
Property, Plant and Accrued Asset Removal Costs	Plant, Property, and Accrued Asset Removal Costs Plant and property are stated at cost, including capitalized labor, materials, and overhead. In accordance with regulatory accounting standards, the cost of acquiring and constructing long-lived plant and property generally includes an allowance for funds used during construction (AFUDC) or capitalized interest. AFUDC represents the regulatory financing cost incurred when debt and equity funds are used for construction (see “ AFUDC ” below). When constructed assets are subject to market-based rates rather than cost-based rates, the financing costs incurred during construction are included in capitalized interest in accordance with U.S. GAAP, not as regulatory financing costs under AFUDC. In accordance with long-standing regulatory treatment, our depreciation rates consist of three components: one based on the average service life of the asset, a second based on the estimated salvage value of the asset, and a third based on the asset’s estimated cost of removal. We collect, through rates, the estimated cost of removal on certain regulated properties through depreciation expense, with a corresponding offset to accumulated depreciation. These removal costs are non-legal obligations as defined by regulatory accounting guidance. Therefore, we have included these costs as non-current regulatory liabilities rather than as accumulated depreciation on our consolidated balance sheets. In the rate setting process, the liability for removal costs is treated as a reduction to the net rate base on which the NGD business has the opportunity to earn its allowed rate of return. The costs of NGD plant retired or otherwise disposed of are removed from NGD plant and charged to accumulated depreciation for recovery or refund through future rates. Gains from the sale of regulated assets are generally deferred and refunded to customers. For assets not related to NGD, we record a gain or loss upon the disposal of the property, and the gain or loss is recorded in operating income or loss in the consolidated statements of comprehensive income. The provision for depreciation of NGD property, plant, and equipment is recorded under the group method on a straight-line basis with rates computed in accordance with depreciation studies approved by regulatory authorities. The weighted-average depreciation rate for NGD assets in service was approximately 2.9 % for 2019 , and 2.8% for 2018 , and 2017 , reflecting the approximate weighted-average economic life of the property. This includes 2019 weighted-average depreciation rates for the following asset categories: 2.6 % for transmission and distribution plant, 2.2 % for gas storage facilities, 5.7 % for general plant, and 4.7 % for intangible and other fixed assets. AFUDC. Certain additions to NGD plant include AFUDC, which represents the net cost of debt and equity funds used during construction. AFUDC is calculated using actual interest rates for debt and authorized rates for ROE, if applicable. If short-term debt balances are less than the total balance of construction work in progress, then a composite AFUDC rate is used to represent interest on all debt funds, shown as a reduction to interest charges, and on ROE funds, shown as other income. While cash is not immediately recognized from recording AFUDC, it is realized in future years through rate recovery resulting from the higher NGD cost of service. Our composite AFUDC rate was 3.9 % in 2019 , 5.2 % in 2018 , and 5.5 % in 2017 . IMPAIRMENT OF LONG-LIVED ASSETS. We review the carrying value of long-lived assets whenever events or changes in circumstances indicate the carrying amount of the assets may not be recoverable. Factors that would necessitate an impairment assessment of long-lived assets include a significant adverse change in the extent or manner in which the asset is used, a significant adverse change in legal factors or business climate that could affect the value of the asset, or a significant decline in the observable market value or expected future cash flows of the asset, among others. When such factors are present, we assess the recoverability by determining whether the carrying value of the asset will be recovered through expected future cash flows. An asset is determined to be impaired when the carrying value of the asset exceeds the expected undiscounted future cash flows from the use and eventual disposition of the asset. If an impairment is indicated, we record an impairment loss for the difference between the carrying value and the fair value of the long-lived assets. Fair value is estimated using appropriate valuation methodologies, which may include an estimate of discounted cash flows. In the fourth quarter of 2017, a non-cash pre-tax impairment of long-lived assets at the Gill Ranch Facility of $192.5 million was recognized. The income approach was used to estimate fair value, using the estimated future net cash flows. We also compared the results of the income approach to our own recent sale experience and recent market comparable transactions in order to estimate fair value. The Gill Ranch Facility was originally included in the gas storage segment, which has since been eliminated, and is now included in discontinued operations. We determined circumstances existed that indicated the carrying value of the assets may not be recoverable. Those circumstances included the completion of a comprehensive strategic review process that evaluated various alternatives including a potential sale, as well as contracting for available storage at lower than anticipated values for the coming storage year. Given these considerations, management re-evaluated the estimated cash flows from our interests in the Gill Ranch Facility, and determined that those estimated cash flows were no longer sufficient to cover the carrying value of the assets. The results of Gill Ranch have been presented as a discontinued operation for NW Holdings and NW Natural on the consolidated statements of comprehensive income and cash flows, and the assets and liabilities associated with Gill Ranch have been classified as discontinued operations assets and liabilities on the consolidated balance sheets. See Note 19 for additional information.
Cash and Cash Equivalents	Cash and Cash Equivalents For purposes of reporting cash flows, cash and cash equivalents include cash on hand plus highly liquid investment accounts with original maturity dates of three months or less. At December 31, 2019 and 2018 , NW Holdings had outstanding checks of approximately $ 3.2 million and $ 2.7 million , respectively, substantially all of which is recorded at NW Natural. These balances are included in accounts payable in the NW Holdings and NW Natural balance sheets.
Revenue Recognition and Accrued Unbilled Revenue	Revenue Recognition and Accrued Unbilled Revenue Revenues, derived primarily from the sale and transportation of natural gas, are recognized upon delivery of the gas commodity or service to customers. Revenues include accruals for gas or water delivered but not yet billed to customers based on estimates of deliveries from meter reading dates to month end (accrued unbilled revenue). Accrued unbilled revenue is dependent upon a number of factors that require management’s judgment, including total natural gas receipts and deliveries, customer use of natural gas or water by billing cycle, and weather factors. Accrued unbilled revenue is reversed the following month when actual billings occur. NW Holdings' accrued unbilled revenue at December 31, 2019 and 2018 was $56.2 million and $57.8 million respectively, substantially all of which is accrued unbilled revenue at NW Natural. Revenues not related to NGD are derived primarily from Interstate Storage Services, asset management activities at the Mist gas storage facility, and other investments and business activities. At the Mist underground storage facility, revenues are primarily firm service revenues in the form of fixed monthly reservation charges. In addition, we also have asset management service revenue from an independent energy marketing company that optimizes commodity, storage, and pipeline capacity release transactions. Under this agreement, guaranteed asset management revenue is recognized using a straight-line, pro-rata methodology over the term of each contract. Revenues earned above the guaranteed amount are recognized as they are earned.
Revenue Taxes	Revenue Taxes Revenue-based taxes are primarily franchise taxes, which are collected from customers and remitted to taxing authorities. In 2018, revenue taxes are included in operating expenses in the statements of comprehensive income for NW Holdings and NW Natural. In 2017 and 2016, revenue taxes are included in operating revenues in the statements of comprehensive income for NW Holdings and NW Natural. All revenue taxes are recorded at NW Natural and were $30.3 million , $30.1 million , and $19.1 million for 2019 , 2018 , and 2017 , respectively.
Accounts Receivable and Allowance for Uncollectible Accounts	Accounts Receivable and Allowance for Uncollectible Accounts Accounts receivable consist primarily of amounts due for natural gas sales and transportation services to NGD customers, plus amounts due for gas storage services. At NW Holdings and NW Natural we establish allowances for uncollectible accounts (allowance) for trade receivables, including accrued unbilled revenue, based on the aging of receivables, collection experience of past due account balances including payment plans, and historical trends of write-offs as a percent of revenues. A specific allowance is established and recorded for large individual customer receivables when amounts are identified as unlikely to be partially or fully recovered. Inactive accounts are written-off against the allowance after they are 120 days past due or when deemed uncollectible. Differences between the estimated allowance and actual write-offs will occur based on a number of factors, including changes in economic conditions, customer creditworthiness, and natural gas prices. The allowance for uncollectible accounts is adjusted quarterly, as necessary, based on information currently available.
Inventories	Inventories NGD gas inventories, which consist of natural gas in storage for NGD customers, are stated at the lower of weighted-average cost or net realizable value. The regulatory treatment of these inventories provides for cost recovery in customer rates. NGD gas inventories injected into storage are priced in inventory based on actual purchase costs, and those withdrawn from storage are charged to cost of gas during the period they are withdrawn at the weighted-average inventory cost. Gas storage inventories, which primarily represent inventories at the Gill Ranch Facility and are included in Discontinued operations - current assets on the consolidated balance sheets, mainly consist of natural gas received as fuel-in-kind from storage customers. Gas storage inventories are valued at the lower of average cost or net realizable value. Cushion gas is not included in inventory balances, is recorded at original cost, and is classified as a long-term plant asset. Materials and supplies inventories consist of inventories both related to and unrelated to NGD and are stated at the lower of average cost or net realizable value. NW Natural's NGD and gas storage inventories totaled $ 27.5 million and $ 29.9 million at 2019 and 2018 , respectively. At December 31, 2019 and 2018 , NW Holdings' materials and supplies inventories, which are comprised primarily of NW Natural's materials and supplies, totaled $ 16.5 million and $ 14.2 million , respectively.
Gas Reserves	Gas Reserves Gas reserves are payments to acquire and produce natural gas reserves. Gas reserves are stated at cost, adjusted for regulatory amortization, with the associated deferred tax benefits recorded as liabilities on the balance sheet. The current portion is calculated based on expected gas deliveries within the next fiscal year. NW Natural recognizes regulatory amortization of this asset on a volumetric basis calculated using the estimated gas reserves and the estimated therms extracted and sold each month. The amortization of gas reserves is recorded to cost of gas along with gas production revenues and production costs. See Note 13 .
Derivatives	Derivatives NW Natural's derivatives are measured at fair value and recognized as either assets or liabilities on the balance sheet. Changes in the fair value of the derivatives are recognized in earnings unless specific regulatory or hedge accounting criteria are met. Accounting for derivatives and hedges provides an exception for contracts intended for normal purchases and normal sales for which physical delivery is probable. In addition, certain derivative contracts are approved by regulatory authorities for recovery or refund through customer rates. Accordingly, the changes in fair value of these approved contracts are deferred as regulatory assets or liabilities pursuant to regulatory accounting principles. NW Natural's financial derivatives generally qualify for deferral under regulatory accounting. NW Natural's index-priced physical derivative contracts also qualify for regulatory deferral accounting treatment. Derivative contracts entered into for NGD requirements after the annual PGA rate has been set and maturing during the PGA year are subject to the PGA incentive sharing mechanism. In Oregon, NW Natural participates in a PGA sharing mechanism under which it is required to select either an 80% or 90% deferral of higher or lower gas costs such that the impact on current earnings from the gas cost sharing is either 20% or 10% of gas cost differences compared to PGA prices, respectively. For each of the PGA years in Oregon beginning November 1, 2019 , 2018 , and 2017 , NW Natural selected the 90% deferral of gas cost differences. In Washington, 100% of the differences between the PGA prices and actual gas costs are deferred. See Note 16 . NW Natural's financial derivatives policy sets forth the guidelines for using selected derivative products to support prudent risk management strategies within designated parameters. NW Natural's objective for using derivatives is to decrease the volatility of gas prices and cash flows without speculative risk. The use of derivatives is permitted only after the risk exposures have been identified, are determined not to exceed acceptable tolerance levels, and are determined necessary to support normal business activities. NW Natural does not enter into derivative instruments for trading purposes. All derivatives for NW Holdings are currently held at NW Natural.
Fair Value	Fair Value In accordance with fair value accounting, we use the following fair value hierarchy for determining inputs for our debt, pension plan assets, and derivative fair value measurements: • Level 1: Valuation is based on quoted prices for identical instruments traded in active markets; • Level 2: Valuation is based on quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model-based valuation techniques for which all significant assumptions are observable in the market; and • Level 3: Valuation is generated from model-based techniques that use significant assumptions not observable in the market. These unobservable assumptions reflect our own estimates of assumptions market participants would use in valuing the asset or liability. In addition, the fair value for certain pension trust investments is determined using Net Asset Value per share (NAV) as a practical expedient, and therefore they are not classified within the fair value hierarchy. These investments primarily consist of institutional investment products. When developing fair value measurements, it is our policy to use quoted market prices whenever available or to maximize the use of observable inputs and minimize the use of unobservable inputs when quoted market prices are not available. Fair values are primarily developed using industry-standard models that consider various inputs including: (a) quoted future prices for commodities; (b) forward currency prices; (c) time value; (d) volatility factors; (e) current market and contractual prices for underlying instruments; (f) market interest rates and yield curves; (g) credit spreads; and (h) other relevant economic measures. NW Natural considers liquid points for natural gas hedging to be those points for which there are regularly published prices in a nationally recognized publication or where the instruments are traded on an exchange.
Goodwill	Goodwill and Business Combinations NW Holdings, through its wholly-owned subsidiary NWN Water and NW Water's wholly-owned subsidiaries, has completed various acquisitions that resulted in the recognition of goodwill. Goodwill is measured as the excess of the acquisition-date fair value of the consideration transferred over the acquisition-date fair value of the net identifiable assets assumed. Adjustments are recorded during the measurement period to finalize the allocation of the purchase price. The carrying value of goodwill is reviewed annually during the fourth quarter using balances as of October 1, or whenever events or changes in circumstance indicate that such carrying values may not be recoverable. The goodwill assessment policy begins with a qualitative analysis in which events and circumstances are evaluated, including macroeconomic conditions, industry and market conditions, regulatory environments, and overall financial performance of the reporting unit. If the qualitative assessment indicates that the carrying value may be at risk of recoverability, a quantitative evaluation is performed to measure the carrying value of the goodwill against the fair value of the reporting unit. The reporting unit is determined primarily based on current operating segments and the level of review provided by the Chief Operating Decision Maker (CODM) and/or segment management on the operating segment's financial results. Reporting units are evaluated periodically for changes in the corporate environment. As of December 31, 2019 and 2018 , NW Holdings had goodwill of $49.9 million and $9.0 million , respectively. All of NW Holdings' goodwill was acquired in 2018 and 2019 through the business combinations completed by NWN Water and its wholly-owned subsidiaries. No impairment charges were recorded as a result of the fourth quarter goodwill impairment assessment.
Income Taxes	Income Taxes We account for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the enactment date period unless, for NW Natural, a regulatory order specifies deferral of the effect of the change in tax rates over a longer period of time. For NW Natural, deferred income tax assets and liabilities are also recognized for temporary differences where the deferred income tax benefits or expenses have previously been flowed through in the ratemaking process of the NGD business. Regulatory tax assets and liabilities are recorded on these deferred tax assets and liabilities to the extent it is believed they will be recoverable from or refunded to customers in future rates. Deferred investment tax credits on NGD plant additions, which reduce income taxes payable, are deferred for financial statement purposes and amortized over the life of the related plant. NW Holdings files consolidated or combined income tax returns that include NW Natural. Income tax expense is allocated on a separate company basis incorporating certain consolidated return considerations. Subsidiary income taxes payable or receivable are generally settled with NW Holdings, the common agent for income tax matters. Interest and penalties related to unrecognized tax benefits, if any, are recognized within income tax expense and accrued interest and penalties are recognized within the related tax liability line in the consolidated balance sheets. No accrued interest or penalties for uncertain tax benefits have been recorded. See Note 11 .
Environmental Contingencies	Environmental Contingencies Loss contingencies are recorded as liabilities when it is probable a liability has been incurred and the amount of the loss is reasonably estimable in accordance with accounting standards for contingencies. Estimating probable losses requires an analysis of uncertainties that often depend upon judgments about potential actions by third parties. Accruals for loss contingencies are recorded based on an analysis of potential results. With respect to environmental liabilities and related costs, estimates are developed based on a review of information available from numerous sources, including completed studies and site specific negotiations. NW Natural's policy is to accrue the full amount of such liability when information is sufficient to reasonably estimate the amount of probable liability. When information is not available to reasonably estimate the probable liability, or when only the range of probable liabilities can be estimated and no amount within the range is more likely than another, it is our policy to accrue at the low end of the range. Accordingly, due to numerous uncertainties surrounding the course of environmental remediation and the preliminary nature of several site investigations, in some cases, it may not be possible to reasonably estimate the high end of the range of possible loss. In those cases, the nature of the potential loss and the fact that the high end of the range cannot be reasonably estimated is disclosed. See Note 18 .
Subsequent Events	Subsequent Events We monitor significant events occurring after the balance sheet date and prior to the issuance of the financial statements to determine the impacts, if any, of events on the financial statements to be issued. Refer to Note 20 for our subsequent events.

Significant Accounting Polici_3

Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Schedule of Regulatory Assets	Amounts NW Natural deferred as regulatory assets and liabilities were as follows: Regulatory Assets In thousands 2019 2018 Current: Unrealized loss on derivatives (1) $ 2,000 $ 12,381 Gas costs 20,140 2,873 Environmental costs (2) 4,762 5,601 Decoupling (3) 1,969 9,140 Pension balancing (4) 5,939 — Income taxes 2,209 2,218 Other (5) 4,910 9,717 Total current $ 41,929 $ 41,930 Non-current: Unrealized loss on derivatives (1) $ 609 $ 3,025 Pension balancing (4) 48,251 74,173 Income taxes 17,173 19,185 Pension and other postretirement benefit liabilities 173,262 174,993 Environmental costs (2) 87,624 76,149 Gas costs 2,866 9,978 Decoupling (3) — 2,545 Other (5) 13,361 11,738 Total non-current $ 343,146 $ 371,786
Schedule of Regulatory Liabilities	Regulatory Liabilities In thousands 2019 2018 Current: Gas costs $ 1,223 $ 17,182 Unrealized gain on derivatives (1) 6,622 8,740 Decoupling (3) 4,831 2,264 Income taxes (6) 8,435 — Other (5) 23,546 19,250 Total current $ 44,657 $ 47,436 Non-current: Gas costs $ 2,013 $ 552 Unrealized gain on derivatives (1) 3,337 725 Decoupling (3) 6,378 — Income taxes (6) 198,219 225,408 Accrued asset removal costs (7) 401,893 380,464 Other (5) 13,877 4,411 Total non-current $ 625,717 $ 611,560 (1) Unrealized gains or losses on derivatives are non-cash items and, therefore, do not earn a rate of return or a carrying charge. These amounts are recoverable through natural gas distribution rates as part of the annual Purchased Gas Adjustment (PGA) mechanism when realized at settlement. (2) Refer to the Environmental Cost Deferral and Recovery table in Note 18 for a description of environmental costs. (3) This deferral represents the margin adjustment resulting from differences between actual and expected volumes. (4) Refer to Note 10 for information regarding the deferral of pension expenses. (5) Balances consist of deferrals and amortizations under approved regulatory mechanisms and typically earn a rate of return or carrying charge. (6) This balance represents estimated amounts associated with the Tax Cuts and Jobs Act. See Note 11 . (7) Estimated costs of removal on certain regulated properties are collected through rates. See "Accounting Policies— Plant, Property, and Accrued Asset Removal Costs " below.

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2019
Earnings Per Share [Abstract]
EPS Calculation [Table Text Block]	NW Holdings' diluted earnings or loss per share are calculated as follows: In thousands, except per share data 2019 2018 2017 Net income from continuing operations $ 65,311 $ 67,311 $ 72,073 Loss from discontinued operations, net of tax (3,576 ) (2,742 ) (127,696 ) Net income (loss) $ 61,735 $ 64,569 $ (55,623 ) Average common shares outstanding - basic 29,786 28,803 28,669 Additional shares for stock-based compensation plans (See Note 8) 73 70 84 Average common shares outstanding - diluted 29,859 28,873 28,753 Earnings from continuing operations per share of common stock: Basic $ 2.19 $ 2.34 $ 2.51 Diluted 2.19 2.33 2.51 Loss from discontinued operations per share of common stock: Basic $ (0.12 ) $ (0.10 ) $ (4.45 ) Diluted (0.12 ) (0.09 ) (4.44 ) Earnings (loss) per share of common stock: Basic $ 2.07 $ 2.24 $ (1.94 ) Diluted 2.07 2.24 (1.93 ) Additional information: Anti-dilutive shares — 2 13

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2019
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	The following table presents summary financial information concerning the reportable segment and other for continuing operations. See Note 19 for information regarding discontinued operations for NW Holdings and NW Natural. In thousands NGD Other NW Natural Other NW Holdings 2019 Operating revenues $ 720,528 $ 19,416 $ 739,944 $ 6,428 $ 746,372 Depreciation and amortization 89,415 990 90,405 1,091 91,496 Income (loss) from operations 135,918 11,428 147,346 (3,872 ) 143,474 Net income (loss) from continuing operations 60,828 8,146 68,974 (3,663 ) 65,311 Capital expenditures 219,880 1,500 221,380 2,091 223,471 Total assets at December 31, 2019 (1) 3,273,835 47,652 3,321,487 91,833 3,413,320 2018 Operating revenues $ 680,648 $ 24,923 $ 705,571 $ 572 $ 706,143 Depreciation and amortization 83,732 1,254 84,986 170 85,156 Income (loss) from operations 118,095 15,004 133,099 (937 ) 132,162 Net income (loss) from continuing operations 57,491 10,558 68,049 (738 ) 67,311 Capital expenditures 212,323 2,005 214,328 308 214,636 Total assets at December 31, 2018 (1) 3,141,969 50,767 3,192,736 36,657 3,229,393 2017 Operating revenues $ 732,942 $ 22,096 $ 755,038 $ — $ 755,038 Depreciation and amortization 79,734 1,290 81,024 29 81,053 Income (loss) from operations (2) 138,450 12,472 150,922 (20 ) 150,902 Net income from continuing operations 60,509 11,211 71,720 353 72,073 Capital expenditures 211,672 1,653 213,325 — 213,325 Total assets at December 31, 2017 (1) 2,961,326 50,471 3,011,797 14,075 3,025,872 (1) Total assets for NW Holdings exclude assets related to discontinued operations of $15.1 million , $13.3 million and $13.9 million as of December 31, 2019 , 2018 , and 2017 , respectively. Total assets for NW Natural exclude assets related to discontinued operations of $31.9 million as of December 31, 2017. (2) Includes $1.0 million of tax expense in NGD, $4.0 million of tax benefit in Other (NW Natural), and $0.4 million of tax benefit in Other (NW Holdings) from the TCJA remeasurement for the year ended December 31, 2017.
Utility Margin	The following table presents additional segment information concerning NGD margin: In thousands 2019 2018 2017 NGD margin calculation: NGD operating revenues $ 720,528 $ 680,648 $ 732,942 Less: NGD cost of gas 255,135 255,743 325,019 Environmental remediation expense 12,337 11,127 15,291 Revenue taxes (1) 30,325 30,082 — NGD margin $ 422,731 $ 383,696 $ 392,632 (1) The change in presentation of revenue taxes was a result of the adoption of ASU 2014-09 "Revenue From Contracts with Customers" and all related amendments on January 1, 2018. This change had no impact on NGD margin results as revenue taxes were previously presented net in NGD operating revenue. For additional information, see Note 2 .

Common Stock (Tables)

Common Stock (Tables)	12 Months Ended
	Dec. 31, 2019
Common Stock [Abstract]
Summary Of Common Stock Shares Issued And Outstanding Table	The following table summarizes the changes in the number of shares of NW Holdings' common stock issued and outstanding: In thousands Shares Balance, December 31, 2016 28,630 Sales to employees under ESPP 18 Stock-based compensation 88 Balance, December 31, 2017 28,736 Sales to employees under ESPP 19 Stock-based compensation 64 Sales to shareholders under DRPP 61 Balance, December 31, 2018 28,880 Sales to employees under ESPP 18 Stock-based compensation 83 Equity Issuance 1,438 Sales to shareholders under DRPP 53 Balance, December 31, 2019 30,472

Revenue (Tables)

Revenue (Tables)	12 Months Ended
	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	The following table presents disaggregated revenue from continuing operations: Year ended December 31, 2019 In thousands NGD Other (NW Natural) NW Natural Other (NW Holdings) NW Holdings Natural gas sales $ 729,296 $ — $ 729,296 $ — $ 729,296 Gas storage revenue, net — 10,240 10,240 — 10,240 Asset management revenue, net — 3,705 3,705 — 3,705 Appliance retail center revenue — 5,471 5,471 — 5,471 Other revenue 847 — 847 6,428 7,275 Revenue from contracts with customers 730,143 19,416 749,559 6,428 755,987 Alternative revenue (20,984 ) — (20,984 ) — (20,984 ) Leasing revenue 11,369 — 11,369 — 11,369 Total operating revenues $ 720,528 $ 19,416 $ 739,944 $ 6,428 $ 746,372

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Lessee, Leases, Supplemental Cash Flow Information [Table Text Block]	Supplemental cash flow information related to leases was as follows: Year ended December 31, 2019 NW Natural Other NW Holdings Cash paid for amounts included in the measurement of lease liabilities Operating cash flows from operating leases $ 4,447 $ 182 $ 4,629 Finance cash flows from finance leases 120 — 120 Right of use assets obtained in exchange for lease obligations Operating leases $ 7,205 $ 372 $ 7,577 Finance leases 312 — 312
Lessee, Operating Lease, Liability, Maturity [Table Text Block]	Maturities of operating lease liabilities at December 31, 2019 were as follows: In thousands NW Natural Other NW Holdings 2020 $ 2,029 $ 126 $ 2,155 2021 143 52 195 2022 111 18 129 2023 88 — 88 2024 89 — 89 Thereafter 526 — 526 Total lease payments 2,986 196 3,182 Less: imputed interest 235 5 240 Total lease obligations 2,751 191 2,942 Less: current obligations 1,979 122 2,101 Long-term lease obligations $ 772 $ 69 $ 841	The following table reflects NW Natural's future minimum lease payments due under non-cancelable operating leases for continuing operations at December 31, 2018. These commitments relate principally to the lease of the corporate operations center and underground gas storage facilities. In thousands Minimum lease payments 2019 $ 5,368 2020 4,812 2021 7,077 2022 7,223 2023 7,304 Thereafter 149,881 Total $ 181,665
Lease, Cost [Table Text Block]	The components of lease expense, a portion of which is capitalized, were as follows: Year ended December 31, 2019 In thousands NW Natural Other NW Holdings Operating lease expense $ 4,620 $ 191 $ 4,811 Short-term lease expense 1,146 — 1,146
Operating Lease, Lease Income [Table Text Block]	The components of lease revenue at NW Natural were as follows: In thousands Year ended December 31, 2019 Lease revenue Operating leases $ 171 Sales-type leases 11,198 Total lease revenue $ 11,369
Lessor, Operating Lease, Payments to be Received, Maturity [Table Text Block]	Total future minimum lease payments to be received under non-cancelable leases at NW Natural at December 31, 2019 are as follows: In thousands Operating Sales-Type Total 2020 $ 65 $ 18,228 $ 18,293 2021 49 17,518 17,567 2022 45 17,026 17,071 2023 45 16,557 16,602 2024 45 15,867 15,912 Thereafter 93 264,740 264,833 Total lease revenue $ 342 $ 349,936 $ 350,278 Less: imputed interest 202,319 Total leases receivable $ 147,617
Operating Lease, Lease Asset and Liabilities [Table Text Block]	Supplemental balance sheet information related to operating leases as of December 31, 2019 is as follows: In thousands NW Natural Other NW Holdings Operating lease right of use assets $ 2,760 $ 190 $ 2,950 Operating lease liabilities - current liabilities $ 1,979 $ 122 $ 2,101 Operating lease liabilities - non-current liabilities 772 69 841 Total operating lease liabilities $ 2,751 $ 191 $ 2,942

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Schedule of Maturities of Long-term Debt [Table Text Block]	Retirement of long-term debt for each of the annual periods through December 31, 2024 and thereafter are as follows: In thousands Long-term debt maturities 2020 $ 75,000 2021 60,000 2022 — 2023 90,000 2024 — Thereafter 624,700
Schedule of Debt [Table Text Block]	The following table presents debt outstanding as of December 31: In thousands 2019 2018 NW Natural First Mortgage Bonds: 8.310% Series due 2019 $ — $ 10,000 7.630% Series due 2019 — 20,000 5.370% Series due 2020 75,000 75,000 9.050% Series due 2021 10,000 10,000 3.176% Series due 2021 50,000 50,000 3.542% Series due 2023 50,000 50,000 5.620% Series due 2023 40,000 40,000 7.720% Series due 2025 20,000 20,000 6.520% Series due 2025 10,000 10,000 7.050% Series due 2026 20,000 20,000 3.211% Series due 2026 35,000 35,000 7.000% Series due 2027 20,000 20,000 2.822% Series due 2027 25,000 25,000 6.650% Series due 2027 19,700 19,700 6.650% Series due 2028 10,000 10,000 3.141% Series due 2029 50,000 — 7.740% Series due 2030 20,000 20,000 7.850% Series due 2030 10,000 10,000 5.820% Series due 2032 30,000 30,000 5.660% Series due 2033 40,000 40,000 5.250% Series due 2035 10,000 10,000 4.000% Series due 2042 50,000 50,000 4.136% Series due 2046 40,000 40,000 3.685% Series due 2047 75,000 75,000 4.110% Series due 2048 50,000 50,000 3.869% Series due 2049 90,000 — Long-term debt, gross 849,700 739,700 Less: current maturities 75,000 30,000 Total long-term debt $ 774,700 $ 709,700
Fair Value Of Long Term Debt Table [Text Block]	The following table provides an estimate of the fair value of NW Natural's long-term debt, including current maturities of long-term debt, using market prices in effect on the valuation date : December 31, In thousands 2019 2018 Gross long-term debt $ 849,700 $ 739,700 Unamortized debt issuance costs (5,712 ) (5,577 ) Carrying amount $ 843,988 $ 734,123 Estimated fair value $ 919,835 $ 760,222

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]	In thousands 2019 2018 2017 Operations and maintenance expense, for stock-based compensation $ 2,172 $ 2,489 $ 2,354 Income tax benefit (575 ) (659 ) (930 ) Net stock-based compensation effect on net income (loss) 1,597 1,830 1,424 Amounts capitalized for stock-based compensation $ 430 $ 531 $ 528
Share-based Payment Arrangement, Option, Activity [Table Text Block]	Option Shares Weighted - Average Price Per Share Intrinsic Value (In millions) Balance outstanding and exercisable, December 31, 2016 180,163 $ 44.38 $ 2.8 Exercised (88,275 ) 44.33 1.8 Forfeited (200 ) 41.15 n/a Balance outstanding and exercisable, December 31, 2017 91,688 44.43 1.4 Exercised (35,450 ) 43.61 0.8 Forfeited (300 ) 43.29 n/a Balance outstanding and exercisable, December 31, 2018 55,938 44.96 0.9 Exercised (45,000 ) 44.79 1.0 Expired — — n/a Balance outstanding and exercisable, December 31, 2019 10,938 $ 45.67 $ 0.3
Share-based Payment Arrangement, Restricted Stock and Restricted Stock Unit, Activity [Table Text Block]	Number of RSUs Weighted - Average Price Per RSU Nonvested, December 31, 2016 89,973 $ 48.85 Granted 32,168 60.51 Vested (35,341 ) 47.07 Forfeited (2,278 ) 53.78 Nonvested, December 31, 2017 84,522 53.90 Granted 32,450 57.59 Vested (32,689 ) 50.75 Forfeited (1,603 ) 59.95 Nonvested, December 31, 2018 82,680 56.47 Granted 36,018 65.29 Vested (35,778 ) 54.22 Forfeited (3,187 ) 63.89 Nonvested, December 31, 2019 79,733 $ 61.17
Share-based Payment Arrangement, Performance Shares, Outstanding Activity [Table Text Block]	The aggregate number of performance shares granted and outstanding at the target and maximum levels were as follows: Dollars in thousands Performance Share Awards Outstanding 2019 Cumulative Expense Performance Period Target Maximum Expense December 31, 2019 2017-19 30,234 60,468 $ 572 $ 1,971 2018-20 — — — — 2019-21 — — — — Total 30,234 60,468 $ 572
Long Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangements by Share-based Payment Award, Performance-Based Units, Vested and Expected to Vest [Table Text Block]	The following table summarizes performance share expense information: Dollars in thousands Shares (1) Expense During Award Year (2) Total Expense for Award Estimated award: 2017-2019 grant (3) 41,573 $ 572 $ 1,971 Actual award: 2016-2018 grant 28,218 598 1,413 2015-2017 grant 18,304 (346 ) 1,169 (1) In addition to common stock shares, a participant also receives a dividend equivalent cash payment equal to the number of shares of common stock received on the award payout multiplied by the aggregate cash dividends paid per share during the performance period. (2) Amount represents the expense recognized in the third year of the vesting period noted above. For the 2015-2017 grant, targets were not met and expense that had been previously recognized was reversed during 2017. (3) This represents the estimated number of shares to be awarded as of December 31, 2019 as certain performance share measures have been achieved. Amounts are subject to change with final payout amounts authorized by the Board of Directors in February 2020 .

Pension and Other Postretirem_2

Pension and Other Postretirement Benefits Costs (Tables)	12 Months Ended
	Dec. 31, 2019
Retirement Benefits [Abstract]
Schedule of Defined Benefit Plans Disclosures	The following table provides a reconciliation of the changes in NW Natural's benefit obligations and fair value of plan assets, as applicable, for NW Natural's pension and other postretirement benefit plans, excluding the Retirement K Savings Plan, and a summary of the funded status and amounts recognized in NW Holdings' and NW Natural's consolidated balance sheets as of December 31: Postretirement Benefit Plans Pension Benefits Other Benefits In thousands 2019 2018 2019 2018 Reconciliation of change in benefit obligation: Obligation at January 1 $ 455,568 $ 486,289 $ 28,172 $ 28,927 Service cost 6,308 7,185 244 282 Interest cost 18,683 16,991 1,117 964 Net actuarial (gain) loss 58,269 (32,979 ) 1,809 (327 ) Benefits paid (23,160 ) (21,918 ) (1,774 ) (1,674 ) Obligation at December 31 $ 515,668 $ 455,568 $ 29,568 $ 28,172 Reconciliation of change in plan assets: Fair value of plan assets at January 1 $ 257,797 $ 287,925 $ — $ — Actual return on plan assets 65,104 (25,925 ) — — Employer contributions 13,310 17,715 1,774 1,674 Benefits paid (23,160 ) (21,918 ) (1,774 ) (1,674 ) Fair value of plan assets at December 31 $ 313,051 $ 257,797 $ — $ — Funded status at December 31 $ (202,617 ) $ (197,771 ) $ (29,568 ) $ (28,172 )
Schedule Of Amounts Recognized In Regulatory Assets Or Other Comprehensive Income Loss	The following table presents amounts realized through regulatory assets or in other comprehensive loss (income) for the years ended December 31: Regulatory Assets Other Comprehensive Loss (Income) Pension Benefits Other Postretirement Benefits Pension Benefits In thousands 2019 2018 2017 2019 2018 2017 2019 2018 2017 Net actuarial loss (gain) $ 10,424 $ 14,261 $ 12,177 $ 1,809 $ (327 ) $ (214 ) $ 3,595 $ (677 ) $ 2,777 Amortization of: Prior service cost (7 ) (42 ) (127 ) 468 468 468 — — — Actuarial loss (14,057 ) (18,761 ) (14,802 ) (369 ) (448 ) (696 ) (648 ) (1,052 ) (946 ) Total $ (3,640 ) $ (4,542 ) $ (2,752 ) $ 1,908 $ (307 ) $ (442 ) $ 2,947 $ (1,729 ) $ 1,831
Schedule Of Defined Benefit Plan Amounts In AOCL And Regulatory Assets	The following table presents amounts recognized in regulatory assets and accumulated other comprehensive loss (AOCL) at December 31: Regulatory Assets AOCL Pension Benefits Other Postretirement Benefits Pension Benefits In thousands 2019 2018 2019 2018 2019 2018 Prior service cost (credit) $ — $ 7 $ (1,270 ) $ (1,738 ) $ — $ — Net actuarial loss 166,903 170,535 7,629 6,189 14,484 11,537 Total $ 166,903 $ 170,542 $ 6,359 $ 4,451 $ 14,484 $ 11,537
Schedule of Amounts Recognized in Other Comprehensive Income (Loss)	The following table presents amounts recognized by NW Holdings and NW Natural in AOCL and the changes in AOCL related to NW Natural's non-qualified employee benefit plans: Year Ended December 31, In thousands 2019 2018 Beginning balance $ (7,188 ) $ (8,438 ) Amounts reclassified to AOCL (3,611 ) 642 Amounts reclassified from AOCL: Amortization of actuarial losses 648 1,052 Reclassification of stranded tax effects (1) (1,366 ) — Total reclassifications before tax (4,329 ) 1,694 Tax expense (benefit) 784 (444 ) Total reclassifications for the period (3,545 ) 1,250 Ending balance $ (10,733 ) $ (7,188 ) (1) Reclassification of $1.4 million of income tax effects resulting from the TCJA from accumulated other comprehensive loss to retained earnings was made pursuant to the adoption of ASU 2018-02. See Note 2 .
Schedule of Allocation of Plan Assets	The following table presents the Pension Plan asset target allocation at December 31, 2019 : Asset Category Target Allocation Long government/credit 20 % U.S. large cap equity 18 Non-U.S. equity 18 Absolute return strategies 12 U.S. small/mid cap equity 10 Real estate funds 7 High yield bonds 5 Emerging markets equity 5 Emerging market debt 5
Schedule of Net Benefit Costs	The following table provides the components of net periodic benefit cost for NW Natural's pension and other postretirement benefit plans for the years ended December 31: Pension Benefits Other Postretirement Benefits In thousands 2019 2018 2017 2019 2018 2017 Service cost $ 6,308 $ 7,185 $ 7,090 $ 244 $ 282 $ 341 Interest cost 18,684 16,991 18,111 1,116 964 1,141 Expected return on plan assets (20,854 ) (20,639 ) (20,433 ) — — — Amortization of prior service costs 7 43 127 (468 ) (468 ) (468 ) Amortization of net actuarial loss 14,704 19,813 15,748 368 448 696 Net periodic benefit cost 18,849 23,393 20,643 1,260 1,226 1,710 Amount allocated to construction (2,493 ) (2,764 ) (6,597 ) (86 ) (98 ) (587 ) Amount deferred to regulatory balancing account — (10,314 ) (6,542 ) — — — Net periodic benefit cost charged to expense 16,356 10,315 7,504 1,174 1,128 1,123 Regulatory pension disallowance 10,500 — — — — — Amortization of regulatory balancing account 16,841 — — — — — Net amount charged to expense $ 43,697 $ 10,315 $ 7,504 $ 1,174 $ 1,128 $ 1,123
Sensitivity Analysis Of Retirement Benefit Costs and Benefit Obligations	The following table provides the assumptions used in measuring periodic benefit costs and benefit obligations for the years ended December 31: Pension Benefits Other Postretirement Benefits 2019 2018 2017 2019 2018 2017 Assumptions for net periodic benefit cost: Weighted-average discount rate 4.19 % 3.51 % 3.99 % 4.13 % 3.44 % 3.85 % Rate of increase in compensation 3.25-3.5% 3.25-4.5% 3.25-4.5% n/a n/a n/a Expected long-term rate of return 7.50 % 7.50 % 7.50 % n/a n/a n/a Assumptions for year-end funded status: Weighted-average discount rate 3.16 % 4.20 % 3.52 % 3.11 % 4.13 % 3.44 % Rate of increase in compensation (1) 3.50-6.50% 3.25-4.5% 3.25-4.5% n/a n/a n/a Expected long-term rate of return 7.25 % 7.50 % 7.50 % n/a n/a n/a
Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates	A one percentage point change in assumed health care cost trend rates would have the following effects: In thousands 1% Increase 1% Decrease Effect on net periodic postretirement health care benefit cost $ 49 $ (44 ) Effect on the accumulated postretirement benefit obligation 710 (640 )
Defined Benefit Plan Estimated Future Employer Contributions Benefit Payments and Estimated Future Payments	The following table provides information regarding employer contributions and benefit payments for NW Natural's Pension Plan, non-qualified pension plans, and other postretirement benefit plans for the years ended December 31, and estimated future contributions and payments: In thousands Pension Benefits Other Benefits Employer Contributions: 2018 $ 17,715 $ 1,674 2019 13,310 1,774 2020 (estimated) 31,338 1,756 Benefit Payments: 2017 31,580 1,737 2018 21,918 1,674 2019 23,160 1,774 Estimated Future Benefit Payments: 2020 23,412 1,756 2021 24,304 1,833 2022 25,094 1,848 2023 25,941 1,899 2024 26,757 1,903 2025-2029 148,000 8,945
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	The following tables present the fair value of NW Natural's plan assets, including outstanding receivables and liabilities, of NW Natural's retirement trust fund: In thousands December 31, 2019 Investments Level 1 Level 2 Level 3 Non-Published NAV (1) Total US equity $ — $ — $ — $ 95,604 $ 95,604 International / Global equity 33,168 — — 74,337 107,505 Liability hedging — — — 93,028 93,028 Opportunistic — — — 9,864 9,864 Cash and cash equivalents — — — 7,049 7,049 Total investments $ 33,168 $ — $ — $ 279,882 $ 313,050 December 31, 2018 Investments Level 1 Level 2 Level 3 Non-Published NAV (1) Total US equity $ — $ — $ — $ 85,233 $ 85,233 International / Global equity 24,994 — — 70,017 95,011 Liability hedging — — — 45,659 45,659 Opportunistic — — — 23,186 23,186 Cash and cash equivalents — — — 8,707 8,707 Total investments $ 24,994 $ — $ — $ 232,802 $ 257,796 December 31, 2019 2018 Receivables: Accrued interest and dividend income $ 3,243 $ 1 Due from broker for securities sold — — Total receivables 3,243 1 Liabilities: Due to broker for securities purchased 3,242 — Total investment in retirement trust $ 313,051 $ 257,797 (1) The fair value for these investments is determined using Net Asset Value per share (NAV) as of December 31, as a practical expedient, and therefore they are not classified within the fair value hierarchy. These investments primarily consist of institutional investment products, for which the NAV is generally not publicly available.

Income Tax (Tables)

Income Tax (Tables)	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	The following table provides a reconciliation between income taxes calculated at the statutory federal tax rate and the provision for income taxes reflected in the NW Holdings and NW Natural statements of comprehensive income or loss for December 31: NW Holdings NW Natural Dollars in thousands 2019 2018 2017 2019 2018 2017 Income taxes at federal statutory rate $ 16,370 $ 19,222 $ 39,578 $ 17,438 $ 19,434 $ 39,624 Increase (decrease): State income tax, net of federal 4,422 4,927 5,066 4,716 4,982 5,072 Differences required to be flowed-through by regulatory commissions (5,772 ) 1,302 2,357 (5,772 ) 1,302 2,357 Effect of the TCJA — — (3,376 ) — — (2,956 ) Deferred tax rate differential post-TCJA — (76 ) — — (75 ) — Regulatory settlement (1,129 ) — — (1,129 ) — — Other, net (1,249 ) (1,184 ) (2,617 ) (1,188 ) (1,184 ) (2,619 ) Total provision for income taxes $ 12,642 $ 24,191 $ 41,008 $ 14,065 $ 24,459 $ 41,478 Effective tax rate 16.2 % 26.4 % 36.3 % 16.9 % 26.4 % 36.6 %
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	The provision for current and deferred income taxes consists of the following at December 31: NW Holdings NW Natural In thousands 2019 2018 2017 2019 2018 2017 Current Federal $ 5,530 $ 8,953 $ 19,345 $ 6,755 $ 9,127 $ 19,304 State 1,667 3,785 5,963 2,101 3,846 5,956 7,197 12,738 25,308 8,856 12,973 25,260 Deferred Federal 1,515 9,001 13,869 1,340 9,025 14,371 State 3,930 2,452 1,831 3,869 2,461 1,847 5,445 11,453 15,700 5,209 11,486 16,218 Income tax provision $ 12,642 $ 24,191 $ 41,008 $ 14,065 $ 24,459 $ 41,478
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]	The following table summarizes the tax effect of significant items comprising NW Holdings and NW Natural's deferred income tax balances recorded at December 31: NW Holdings NW Natural In thousands 2019 2018 2019 2018 Deferred tax liabilities: Plant and property $ 269,886 $ 288,385 $ 281,044 $ 303,186 Leases receivable 40,133 — 40,133 — Pension and postretirement obligations 22,635 27,135 22,635 27,135 Income tax regulatory asset 19,382 21,403 19,382 21,402 Other 751 1,061 410 537 Total deferred income tax liabilities $ 352,787 $ 337,984 $ 363,604 $ 352,260 Deferred income tax assets: Income tax regulatory liability $ 54,259 $ 57,469 $ 54,259 $ 57,469 Other intangible assets 2,723 — — — Net operating losses and credits carried forward 162 52 48 52 Total deferred income tax assets $ 57,144 $ 57,521 $ 54,307 $ 57,521 Total net deferred income tax liabilities $ 295,643 $ 280,463 $ 309,297 $ 294,739

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2019
Public Utilities, Property, Plant and Equipment [Abstract]
Major Classifications Of Property, Plant And Equipment And Accumulated Depreciation [Text Block]	The following table sets forth the major classifications of property, plant, and equipment and accumulated depreciation of continuing operations at December 31: In thousands 2019 2018 NW Natural: NGD plant in service $ 3,302,049 $ 3,134,122 NGD work in progress 84,965 204,978 Less: Accumulated depreciation 1,017,931 974,252 NGD plant, net 2,369,083 2,364,848 Other plant in service 63,513 66,009 Other construction work in progress 5,548 5,330 Less: Accumulated depreciation 18,662 18,603 Other plant, net (1) 50,399 52,736 Total property, plant, and equipment $ 2,419,482 $ 2,417,584 Other (NW Holdings): Other plant in service $ 20,671 $ 4,051 Less: Accumulated depreciation 1,254 263 Other plant, net (1) 19,417 3,788 NW Holdings: Total property, plant, and equipment $ 2,438,899 $ 2,421,372 NW Natural and NW Holdings: Capital expenditures in accrued liabilities $ 32,502 $ 23,676 (1) NW Natural previously reported other balances which were restated due to certain assets and liabilities now being classified as discontinued operations assets and liabilities in its balance sheets. See Note 19 for further discussion.

Gas Reserves (Tables)

Gas Reserves (Tables)	12 Months Ended
	Dec. 31, 2019
Gas Reserves [Abstract]
Gas Reserves Table [Text Block]	The following table outlines NW Natural's net gas reserves investment at December 31: In thousands 2019 2018 Gas reserves, current $ 15,278 $ 16,647 Gas reserves, non-current 172,029 170,660 Less: Accumulated amortization 123,635 104,463 Total gas reserves (1) 63,672 82,844 Less: Deferred taxes on gas reserves 15,515 20,071 Net investment in gas reserves $ 48,157 $ 62,773 (1) The net investment in additional wells included in total gas reserves was $3.8 million and $4.8 million at December 31, 2019 and 2018 , respectively.

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2019
Investments [Abstract]
Schedule Of Long Term Investments	The following table summarizes other investments at December 31: NW Holdings NW Natural In thousands 2019 2018 2019 2018 Investments in life insurance policies $ 49,837 $ 49,922 $ 49,837 $ 49,922 Investments in gas pipeline 13,472 13,571 — — Other 24 65 — — Total other investments $ 63,333 $ 63,558 $ 49,837 $ 49,922

Business Combinations Busines_2

Business Combinations Business Combinations (Tables)	12 Months Ended
	Dec. 31, 2019
Business Combinations [Abstract]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block]	The preliminary purchase price for the acquisition has been allocated to the net assets acquired as of the acquisition date and is as follows: In thousands December 31, 2019 Current assets $ 221 Property, plant and equipment 13,819 Goodwill 40,118 Deferred tax assets 812 Current liabilities (22 ) Total net assets acquired $ 54,948

Derivative Instruments (Tables)

Derivative Instruments (Tables)	12 Months Ended
	Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Notional Amounts of Outstanding Derivative Positions	The following table presents the absolute notional amounts related to open positions on NW Natural derivative instruments: At December 31, In thousands 2019 2018 Natural gas (in therms): Financial 651,540 408,850 Physical 512,849 472,275 Foreign exchange $ 6,650 $ 6,936
Income Statement Presentation of Derivative Instruments	The following table reflects the income statement presentation for the unrealized gains and losses from NW Natural's derivative instruments, which also represents all derivative instruments at NW Holdings: December 31, 2019 December 31, 2018 In thousands Natural gas commodity Foreign exchange Natural gas commodity Foreign exchange Benefit (expense) to cost of gas $ 9,863 $ 102 $ (1,239 ) $ (284 ) Operating revenues (expense) (568 ) — 1,660 — Amounts deferred to regulatory accounts on balance sheet (9,376 ) (102 ) (211 ) 284 Total gain (loss) in pre-tax earnings $ (81 ) $ — $ 210 $ —
Table Of Estimated Collateral Calls Table	Credit Rating Downgrade Scenarios In thousands (Current Ratings) A+/A3 BBB+/Baa1 BBB/Baa2 BBB-/Baa3 Speculative With Adequate Assurance Calls $ — $ — $ — $ — $ (66 ) Without Adequate Assurance Calls — — — — (66 )

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Long-term Purchase Commitment	The aggregate amounts of these agreements were as follows at December 31, 2019 : In thousands Gas Pipeline Pipeline 2020 $ 86,175 $ 76,897 $ 4,201 2021 2,899 70,638 3,904 2022 — 68,943 3,904 2023 — 68,563 3,904 2024 — 67,052 3,904 Thereafter — 527,148 3,253 Total 89,074 879,241 23,070 Less: Amount representing interest 481 147,613 840 Total at present value $ 88,593 $ 731,628 $ 22,230

Environmental Matters (Tables)

Environmental Matters (Tables)	12 Months Ended
	Dec. 31, 2019
Environmental Remediation Obligations [Abstract]
Schedule of Environmental Loss Contingencies by Site	The following table summarizes information regarding liabilities related to environmental sites, which are recorded in other current liabilities and other noncurrent liabilities in NW Natural's balance sheet at December 31: Current Liabilities Non-Current Liabilities In thousands 2019 2018 2019 2018 Portland Harbor site: Gasco/Siltronic Sediments $ 11,632 $ 5,117 $ 46,082 $ 44,351 Other Portland Harbor 2,543 2,600 6,920 6,273 Gasco/Siltronic Upland site 14,203 13,983 43,616 44,830 Central Service Center site — 10 — — Front Street site 10,847 11,402 — 3 Oregon Steel Mills — — 179 179 Total $ 39,225 $ 33,112 $ 96,797 $ 95,636
Environmental Regulatory Table	. The following table presents information regarding the total regulatory assets deferred as of December 31: In thousands 2019 2018 Deferred costs and interest (1) $ 36,673 $ 41,883 Accrued site liabilities (2) 135,662 128,369 Insurance proceeds and interest (79,949 ) (88,502 ) Total regulatory asset deferral (1) $ 92,386 $ 81,750 Current regulatory assets (3) 4,762 5,601 Long-term regulatory assets (3) 87,624 76,149 (1) Includes pre-review and post-review deferred costs, amounts currently in amortization, and interest, net of amounts collected from customers. In Oregon, NW Natural earns a carrying charge on cash amounts paid, whereas amounts accrued but not yet paid do not earn a carrying charge until expended. NW Natural also accrues a carrying charge on insurance proceeds for amounts owed to customers. In Washington, neither the cash paid nor insurance proceeds accrue a carrying charge. (2) Excludes 3.32% of the Front Street site liability, or $0.4 million in 2019 and $0.4 million in 2018 , as the OPUC only allows recovery of 96.68% of costs for those sites allocable to Oregon, including those that historically served only Oregon customers. (3) Amounts included in this estimate are still subject to a prudence review by the OPUC and WUTC, and earnings test review by the OPUC. Amounts do not include the $5.0 million tariff rider. See " Oregon SRRM " below.

Discontinued Operations (Tables

Discontinued Operations (Tables)	12 Months Ended
	Dec. 31, 2019
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Groups, Including Discontinued Operations	The following table presents the operating results prior to the holding company reorganization effective October 1, 2018 of NWN Energy, NWN Gas Storage, Gill Ranch, NNG Financial, NWN Water, and NW Holdings, which were historically reported within the gas storage segment and other, and is presented net of tax on NW Natural's consolidated statements of comprehensive income: NW Natural Discontinued Operations In thousands, except per share data 2018 2017 Revenues $ 3,016 $ 7,360 Expenses Operations and maintenance 4,151 7,423 General taxes 448 1,410 Depreciation and amortization 420 4,555 Other expenses and interest 342 650 Impairment expense — 192,478 Total expenses 5,361 206,516 Loss from discontinued operations before income tax (2,345 ) (199,156 ) Income tax benefit (1) (622 ) (71,813 ) Loss from discontinued operations, net of tax $ (1,723 ) $ (127,343 ) (1) 2017 income tax benefit includes approximately $18 million of tax benefit from the enactment of the TCJA. The TCJA was enacted December 22, 2017 and resulted in the federal tax rate changing from 35% to 21% .
Northwest Holdings [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Groups, Including Discontinued Operations	The following table presents the operating results of Gill Ranch, which was historically reported within the gas storage segment, and is presented net of tax on NW Holdings' consolidated statements of comprehensive income: NW Holdings Discontinued Operations In thousands, except per share data 2019 2018 2017 Revenues $ 5,301 $ 3,579 $ 7,135 Expenses Operations and maintenance 8,587 5,771 7,245 General taxes 219 479 1,373 Depreciation and amortization 423 430 4,525 Other expenses and interest 931 609 975 Impairment expense — — 192,478 Total expenses 10,160 7,289 206,596 Loss from discontinued operations before income tax (4,859 ) (3,710 ) (199,461 ) Income tax benefit (1) (1,283 ) (968 ) (71,765 ) Loss from discontinued operations, net of tax $ (3,576 ) $ (2,742 ) $ (127,696 ) Loss from discontinued operations per share of common stock: Basic $ (0.12 ) $ (0.10 ) $ (4.45 ) Diluted (0.12 ) (0.09 ) (4.44 ) (1) 2017 income tax benefit includes approximately $18 million of tax benefit from the enactment of the TCJA. The TCJA was enacted December 22, 2017 and resulted in the federal tax rate changing from 35% to 21% .
Northwest Natural Gas Company [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Groups, Including Discontinued Operations
Northwest Holdings [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Groups, Including Discontinued Operations	The following table presents the carrying amounts of the major components of Gill Ranch that are classified as discontinued operations assets and liabilities on the consolidated balance sheets: NW Holdings Discontinued Operations In thousands 2019 2018 Assets: Accounts receivable $ 333 $ 390 Inventories 695 685 Other current assets 457 333 Property, plant, and equipment 13,291 11,621 Less: Accumulated depreciation 7 7 Operating lease right of use asset 118 — Other non-current assets 247 247 Total discontinued operations assets - current assets (1) $ 15,134 $ 13,269 Liabilities: Accounts payable $ 1,250 $ 873 Other current liabilities 848 307 Operating lease liabilities 116 — Other non-current liabilities 11,495 11,779 Total discontinued operations liabilities - current liabilities (1) $ 13,709 $ 12,959 (1) The total assets and liabilities of Gill Ranch are classified as current as of December 31, 2018 because it was probable that the sale would be completed within one year.

Quarterly Financial Informati_2

Quarterly Financial Information (Tables)	12 Months Ended
	Dec. 31, 2019
Entity Information [Line Items]
Schedule of Quarterly Financial Information [Table Text Block]	NORTHWEST NATURAL HOLDING COMPANY QUARTERLY FINANCIAL INFORMATION (UNAUDITED) NW Holdings Quarter Ended (1) In thousands, except per share data March 31 June 30 September 30 December 31 2019 Operating revenues $ 285,348 $ 123,433 $ 90,317 $ 247,274 Net income (loss) from continuing operations 43,418 2,051 (18,506 ) 38,348 Loss from discontinued operations, net of tax (217 ) (956 ) (795 ) (1,608 ) Net income (loss) $ 43,201 $ 1,095 $ (19,301 ) $ 36,740 Average common shares outstanding: Basic 28,906 29,337 30,429 30,448 Diluted 28,970 29,394 30,429 30,521 Earnings (loss) from continuing operations per share of common stock: Basic $ 1.50 $ 0.07 $ (0.61 ) $ 1.26 Diluted 1.50 0.07 (0.61 ) 1.26 Loss from discontinued operations per share of common stock: Basic $ (0.01 ) $ (0.03 ) $ (0.02 ) $ (0.05 ) Diluted (0.01 ) (0.03 ) (0.02 ) (0.05 ) Earnings (loss) per share of common stock: Basic $ 1.49 $ 0.04 $ (0.63 ) $ 1.21 Diluted 1.49 0.04 (0.63 ) 1.20 2018 Operating revenues $ 263,635 $ 124,567 $ 91,239 $ 226,702 Net income (loss) from continuing operations 42,011 (339 ) (11,144 ) 36,783 Loss from discontinued operations, net of tax (474 ) (659 ) (650 ) (959 ) Net income (loss) $ 41,537 $ (998 ) $ (11,794 ) $ 35,824 Average common shares outstanding: Basic 28,753 28,791 28,815 28,851 Diluted 28,803 28,791 28,815 28,940 Earnings (loss) from continuing operations per share of common stock: Basic $ 1.46 $ (0.01 ) $ (0.39 ) $ 1.27 Diluted 1.46 (0.01 ) (0.39 ) 1.27 Loss from discontinued operations per share of common stock: Basic $ (0.02 ) $ (0.02 ) $ (0.02 ) $ (0.03 ) Diluted (0.02 ) (0.02 ) (0.02 ) (0.03 ) Earnings (loss) per share of common stock: Basic $ 1.44 $ (0.03 ) $ (0.41 ) $ 1.24 Diluted 1.44 (0.03 ) (0.41 ) 1.24 (1)
Northwest Natural Gas Company [Member]
Entity Information [Line Items]
Schedule of Quarterly Financial Information [Table Text Block]	NORTHWEST NATURAL GAS COMPANY QUARTERLY FINANCIAL INFORMATION (UNAUDITED) NW Natural Quarter ended In thousands March 31 June 30 September 30 December 31 2019 Operating revenues $ 284,846 $ 122,242 $ 87,592 $ 245,264 Net income (loss) $ 43,895 $ 3,054 $ (17,588 ) $ 39,613 2018 Operating revenues $ 263,635 $ 124,563 $ 91,227 $ 226,146 Net income (loss) from continuing operations 42,014 (271 ) (11,275 ) 37,581 Loss from discontinued operations, net of tax (477 ) (727 ) (519 ) — Net income (loss) $ 41,537 $ (998 ) $ (11,794 ) $ 37,581

Condensed Financials Standalo_2

Condensed Financials Standalone Holdco NW Holdings Financial Statements (Tables)	12 Months Ended
	Dec. 31, 2019
Condensed Income Statements, Captions [Line Items]
Condensed Income Statement [Table Text Block]	NORTHWEST NATURAL HOLDING COMPANY CONDENSED STATEMENTS OF COMPREHENSIVE INCOME (PARENT COMPANY ONLY) In thousands Year ended December 31, 2019 Inception through December 31, 2018 Operating expenses: Operations and maintenance $ 2,747 $ 838 Total operating expenses 2,747 838 Loss from operations (2,747 ) (838 ) Earnings from investment in subsidiaries, net of tax 64,328 36,469 Other income (expense), net (22 ) 36 Interest expense, net 726 53 Income before income taxes 60,833 35,614 Income tax expense (benefit) (902 ) (225 ) Net income $ 61,735 $ 35,839
Condensed Balance Sheet [Table Text Block]	NORTHWEST NATURAL HOLDING COMPANY CONDENSED BALANCE SHEETS (PARENT COMPANY ONLY) As of December 31, In thousands 2019 2018 Assets: Current assets: Cash and cash equivalents $ 119 4,011 Receivables from affiliates 1,950 2,796 Income taxes receivable 256 6,000 Other current assets 4,600 3,078 Total current assets 6,925 15,885 Non-current assets: Investments in subsidiaries 888,477 754,971 Other investments 24 65 Deferred tax assets 191 — Other non-current assets 245 310 Total non-current assets 888,937 755,346 Total assets $ 895,862 $ 771,231 Liabilities and equity: Current liabilities: Short-term debt $ 24,000 $ — Accounts payable 612 168 Payables to affiliates 3,697 9,166 Taxes accrued 127 — Interest accrued — 32 Other current liabilities 37 — Total current liabilities 28,473 9,366 Long-term debt — (1 ) Deferred credits and other non-current liabilities: Deferred tax liabilities — 7 Total deferred credits and other non-current liabilities — 7 Equity: Common stock 840,364 739,722 Retained earnings 27,025 22,137 Total equity 867,389 761,859 Total liabilities and equity $ 895,862 $ 771,231
Condensed Cash Flow Statement [Table Text Block]	NORTHWEST NATURAL HOLDING COMPANY CONDENSED STATEMENTS OF CASH FLOWS (PARENT COMPANY ONLY) In thousands Year ended December 31, 2019 Inception through December 31, 2018 Operating activities: Net income $ 61,735 $ 35,839 Adjustments to reconcile net income to cash used in operations: Equity in earnings of subsidiaries, net of tax (64,328 ) (36,469 ) Deferred income taxes (198 ) 7 Other 66 15 Changes in assets and liabilities: Receivables, net 846 (585 ) Income and other taxes 4,325 (9,034 ) Accounts payable (5,177 ) 9,304 Interest accrued (32 ) 32 Other, net (346 ) (44 ) Cash used in operating activities (3,109 ) (935 ) Investing activities: Contributions to subsidiaries (157,591 ) (1,804 ) Cash used in investing activities (157,591 ) (1,804 ) Financing activities: Proceeds from stock options exercised 2,015 — Proceeds from common stock issued 92,956 — Change in short-term debt 24,000 — Cash dividend payments received from subsidiaries 88,439 — Cash dividend payments on common stock (53,339 ) (12,923 ) Capital contributions — 20,000 Other 2,737 (327 ) Cash provided by financing activities 156,808 6,750 Increase (decrease) in cash and cash equivalents (3,892 ) 4,011 Cash and cash equivalents, beginning of period 4,011 — Cash and cash equivalents, end of period $ 119 $ 4,011

Condensed Financials Standalo_3

Condensed Financials Standalone Holdco Condensed Balance Sheet (Tables)	12 Months Ended
	Dec. 31, 2019
Condensed Balance Sheet Statements, Captions [Line Items]
Condensed Balance Sheet [Table Text Block]	NORTHWEST NATURAL HOLDING COMPANY CONDENSED BALANCE SHEETS (PARENT COMPANY ONLY) As of December 31, In thousands 2019 2018 Assets: Current assets: Cash and cash equivalents $ 119 4,011 Receivables from affiliates 1,950 2,796 Income taxes receivable 256 6,000 Other current assets 4,600 3,078 Total current assets 6,925 15,885 Non-current assets: Investments in subsidiaries 888,477 754,971 Other investments 24 65 Deferred tax assets 191 — Other non-current assets 245 310 Total non-current assets 888,937 755,346 Total assets $ 895,862 $ 771,231 Liabilities and equity: Current liabilities: Short-term debt $ 24,000 $ — Accounts payable 612 168 Payables to affiliates 3,697 9,166 Taxes accrued 127 — Interest accrued — 32 Other current liabilities 37 — Total current liabilities 28,473 9,366 Long-term debt — (1 ) Deferred credits and other non-current liabilities: Deferred tax liabilities — 7 Total deferred credits and other non-current liabilities — 7 Equity: Common stock 840,364 739,722 Retained earnings 27,025 22,137 Total equity 867,389 761,859 Total liabilities and equity $ 895,862 $ 771,231

Condensed Financials Standalo_4

Condensed Financials Standalone Holdco Condensed Income Statement (Tables)	12 Months Ended
	Dec. 31, 2019
Condensed Income Statements, Captions [Line Items]
Condensed Income Statement [Table Text Block]	NORTHWEST NATURAL HOLDING COMPANY CONDENSED STATEMENTS OF COMPREHENSIVE INCOME (PARENT COMPANY ONLY) In thousands Year ended December 31, 2019 Inception through December 31, 2018 Operating expenses: Operations and maintenance $ 2,747 $ 838 Total operating expenses 2,747 838 Loss from operations (2,747 ) (838 ) Earnings from investment in subsidiaries, net of tax 64,328 36,469 Other income (expense), net (22 ) 36 Interest expense, net 726 53 Income before income taxes 60,833 35,614 Income tax expense (benefit) (902 ) (225 ) Net income $ 61,735 $ 35,839

Condensed Financials Standalo_5

Condensed Financials Standalone Holdco Condensed Cash Flow (Tables)	12 Months Ended
	Dec. 31, 2019
Condensed Cash Flow Statements, Captions [Line Items]
Condensed Cash Flow Statement [Table Text Block]	NORTHWEST NATURAL HOLDING COMPANY CONDENSED STATEMENTS OF CASH FLOWS (PARENT COMPANY ONLY) In thousands Year ended December 31, 2019 Inception through December 31, 2018 Operating activities: Net income $ 61,735 $ 35,839 Adjustments to reconcile net income to cash used in operations: Equity in earnings of subsidiaries, net of tax (64,328 ) (36,469 ) Deferred income taxes (198 ) 7 Other 66 15 Changes in assets and liabilities: Receivables, net 846 (585 ) Income and other taxes 4,325 (9,034 ) Accounts payable (5,177 ) 9,304 Interest accrued (32 ) 32 Other, net (346 ) (44 ) Cash used in operating activities (3,109 ) (935 ) Investing activities: Contributions to subsidiaries (157,591 ) (1,804 ) Cash used in investing activities (157,591 ) (1,804 ) Financing activities: Proceeds from stock options exercised 2,015 — Proceeds from common stock issued 92,956 — Change in short-term debt 24,000 — Cash dividend payments received from subsidiaries 88,439 — Cash dividend payments on common stock (53,339 ) (12,923 ) Capital contributions — 20,000 Other 2,737 (327 ) Cash provided by financing activities 156,808 6,750 Increase (decrease) in cash and cash equivalents (3,892 ) 4,011 Cash and cash equivalents, beginning of period 4,011 — Cash and cash equivalents, end of period $ 119 $ 4,011

Valuation Allowances and Rese_2

Valuation Allowances and Reserves (Tables)	12 Months Ended
	Dec. 31, 2019
Entity Information [Line Items]
Summary of Valuation Allowance	NORTHWEST NATURAL HOLDING COMPANY SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES COLUMN A COLUMN B COLUMN C COLUMN D COLUMN E Additions Deductions In thousands (year ended December 31) Balance at beginning of period Charged to costs and expenses Charged to other accounts Net write-offs Balance at end of period 2019 Reserves deducted in balance sheet from assets to which they apply: Allowance for uncollectible accounts $ 977 $ 450 $ — $ 754 $ 673 2018 Reserves deducted in balance sheet from assets to which they apply: Allowance for uncollectible accounts $ 956 $ 680 $ — $ 659 $ 977 2017 Reserves deducted in balance sheet from assets to which they apply: Allowance for uncollectible accounts $ 1,290 $ 865 $ — $ 1,199 $ 956
Northwest Natural Gas Company [Member]
Entity Information [Line Items]
Summary of Valuation Allowance	NORTHWEST NATURAL GAS COMPANY SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES COLUMN A COLUMN B COLUMN C COLUMN D COLUMN E Additions Deductions In thousands (year ended December 31) Balance at beginning of period Charged to costs and expenses Charged to other accounts Net write-offs Balance at end of period 2019 Reserves deducted in balance sheet from assets to which they apply: Allowance for uncollectible accounts $ 975 $ 450 $ — $ 753 $ 672 2018 Reserves deducted in balance sheet from assets to which they apply: Allowance for uncollectible accounts $ 956 $ 678 $ — $ 659 $ 975 2017 Reserves deducted in balance sheet from assets to which they apply: Allowance for uncollectible accounts $ 1,290 $ 865 $ — $ 1,199 $ 956

Significant Accounting Polici_4

Significant Accounting Policies - Regulatory Asset Disclosure (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Regulatory Assets [Line Items]
Regulatory Assets, Current	$ 41,929	$ 41,930
Regulatory Assets, Noncurrent	343,146	371,786
Northwest Natural Gas Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Current	41,929	41,930
Regulatory Assets, Noncurrent	343,146	371,786
Northwest Natural Gas Company [Member] | Unrealized loss on derivatives [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Current	2,000	12,381
Regulatory Assets, Noncurrent	609	3,025
Northwest Natural Gas Company [Member] | Gas costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Current	20,140	2,873
Regulatory Assets, Noncurrent	2,866	9,978
Northwest Natural Gas Company [Member] | Environmental costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Current	4,762	5,601
Regulatory Assets, Noncurrent	87,624	76,149
Northwest Natural Gas Company [Member] | Decoupling [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Current	1,969	9,140
Regulatory Assets, Noncurrent	0	2,545
Northwest Natural Gas Company [Member] | Income taxes [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Current	2,209	2,218
Regulatory Assets, Noncurrent	17,173	19,185
Northwest Natural Gas Company [Member] | Pension balancing [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Current	5,939	0
Regulatory Assets, Noncurrent	48,251	74,173
Northwest Natural Gas Company [Member] | Pension and other postretirement benefit liabilities [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	173,262	174,993
Northwest Natural Gas Company [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Current	4,910	9,717
Regulatory Assets, Noncurrent	$ 13,361	$ 11,738

Significant Accounting Polici_5

Significant Accounting Policies - Regulatory Liability Disclosure (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	$ 44,657	$ 47,436
Regulatory Liability, Noncurrent	625,717	611,560
Northwest Natural Gas Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	44,657	47,436
Regulatory Liability, Noncurrent	625,717	611,560
Northwest Natural Gas Company [Member] | Gas costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	1,223	17,182
Regulatory Liability, Noncurrent	2,013	552
Northwest Natural Gas Company [Member] | Unrealized gain on derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	6,622	8,740
Regulatory Liability, Noncurrent	3,337	725
Northwest Natural Gas Company [Member] | Decoupling [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	4,831	2,264
Regulatory Liability, Noncurrent	6,378	0
Northwest Natural Gas Company [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	23,546	19,250
Regulatory Liability, Noncurrent	13,877	4,411
Northwest Natural Gas Company [Member] | Income taxes [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	8,435	0
Regulatory Liability, Noncurrent	198,219	225,408
Northwest Natural Gas Company [Member] | Accrued asset removal costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liability, Noncurrent	$ 401,893	$ 380,464

- Narrative (Details)

- Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Accrued Asset Removal Costs [Abstract]
Weighted Average Depreciation Rates Transmission Distribution		2.60%
Weighted Average Depreciation Rates Gas Storage		2.20%
Weighted Average Depreciation Rates General Plant		5.70%
Weighted Average Depreciation Rates Intangible Other		4.70%
Public Utilities, AFUDC, Rate		3.90%	5.20%	5.50%
Revenue Recognition [Abstract]
Accrued unbilled revenue	$ 56,192	$ 56,192	$ 57,827
Revenue Taxes [Abstract]
Operating Expenses		602,898	573,981	$ 604,136
Inventory Disclosure [Abstract]
Inventory, Raw Materials and Supplies, Net of Reserves	16,500	16,500	14,200
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	49,929	49,929	8,954
Goodwill and Intangible Asset Impairment	0
Accounts Payable [Member]
Cash and Cash Equivalents [Abstract]
Bank Overdrafts	3,200	3,200	2,700
Gill Ranch [Member] | Discontinued Operations, Held-for-sale [Member]
Property, Plant and Accrued Asset Removal Costs [Abstract]
Impairment of Long-Lived Assets		$ 0	0	192,478
Northwest Natural Gas Company [Member]
Industry Regulation [Abstract]
Regulatory Asset, Amortization Period		12 months
Regulatory Asset, Amortization Period, Low End of Range		less than one year
Regulatory Liability, Amortization Period		12 months
Regulatory Liability, Amortization Period, Low End Of Range		less than one year
Revenue Recognition [Abstract]
Accrued unbilled revenue	56,139	$ 56,139	57,773
Revenue Taxes [Abstract]
Operating Expenses		592,598	572,472	$ 604,116
Inventory Disclosure [Abstract]
Inventory - Gas	$ 27,500	$ 27,500	$ 29,900
Northwest Natural Gas Company [Member] | Oregon [Member]
Derivative Instruments and Hedging Activities Disclosure [Abstract]
PGA deferral rate		90.00%	90.00%	90.00%
Northwest Natural Gas Company [Member] | Oregon [Member] | Minimum [Member]
Derivative Instruments and Hedging Activities Disclosure [Abstract]
PGA deferral rate		80.00%
Impact on earnings from gas cost sharing		10.00%
Northwest Natural Gas Company [Member] | Oregon [Member] | Maximum [Member]
Derivative Instruments and Hedging Activities Disclosure [Abstract]
PGA deferral rate		90.00%
Impact on earnings from gas cost sharing		20.00%
Northwest Natural Gas Company [Member] | Washington [Member]
Derivative Instruments and Hedging Activities Disclosure [Abstract]
PGA deferral rate		100.00%	100.00%	100.00%
Asset Recoverable Gas Costs [Member] | Northwest Natural Gas Company [Member]
Industry Regulation [Abstract]
Regulatory Liability, Amortization Period		12 months
Other Nonoperating Income (Expense) [Member]
Industry Regulation [Abstract]
Other Nonoperating Income		$ 19,600	$ 7,600
Other Nonoperating Expense		12,300	5,900
Operating Segments [Member] | Northwest Natural Gas Company [Member]
Revenue Taxes [Abstract]
Utilities Operating Expense, Taxes		30,300	30,100	$ 19,100
Natural Gas Distribution [Member] | Operating Segments [Member]
Revenue Taxes [Abstract]
Utilities Operating Expense, Taxes		$ 30,325	$ 30,082	$ 0
Natural Gas Distribution [Member]
Property, Plant and Accrued Asset Removal Costs [Abstract]
Weighted-average depreciation rate, assets in service		2.90%	2.80%	2.80%

Significant Accounting Polici_6

Significant Accounting Policies - Revenue from Contract with Customer (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues	$ 247,274	$ 90,317	$ 123,433	$ 285,348	$ 226,702	$ 91,239	$ 124,567	$ 263,635	$ 746,372	$ 706,143	$ 755,038
Operating Expenses									602,898	$ 573,981	$ 604,136
Northwest Holdings and Northwest Natural [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues									30,300
Operating Expenses									$ 30,300

Significant Accounting Polici_7

Significant Accounting Policies Significant Accounting Policies - Leases ASU 2016-02 (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property, plant, and equipment	$ 3,476,746	$ 3,414,490
Operating Lease, Right-of-Use Asset	2,950	0
Northwest Natural Gas Company [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property, plant, and equipment	3,456,075	3,410,439
Operating Lease, Right-of-Use Asset	2,760	0
Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	0
Operating Leases, Income Statement, Initial Direct Costs	0
Operating Lease, Right-of-Use Asset	7,300
Accounting Standards Update 2016-02 [Member] | Northwest Natural Gas Company [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Lease, Right-of-Use Asset	$ 7,000
Accounting Standards Update 2016-02 [Member] | New Headquarters Lease [Member] | Build to Suit Lease [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property, plant, and equipment		$ 26,000

Significant Accounting Polici_8

Significant Accounting Policies Significant Accounting Policies - AOCI Tax Effects ASU 2018-02 (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of tax effects from the TCJA		$ 0
Accounting Standards Update 2018-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of tax effects from the TCJA	$ 1,400

Earnings Per Share (Details)

Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Line Items]
Net income from continuing operations	$ 38,348	$ (18,506)	$ 2,051	$ 43,418	$ 36,783	$ (11,144)	$ (339)	$ 42,011	$ 65,311	$ 67,311	$ 72,073
Loss from discontinued operations, net of tax	(1,608)	(795)	(956)	(217)	(959)	(650)	(659)	(474)	(3,576)	(2,742)	(127,696)
Net income (loss)	$ 36,740	$ (19,301)	$ 1,095	$ 43,201	$ 35,824	$ (11,794)	$ (998)	$ 41,537	$ 61,735	$ 64,569	$ (55,623)
Average common shares outstanding:
Average common shares outstanding - basic (in shares)	30,448	30,429	29,337	28,906	28,851	28,815	28,791	28,753	29,786	28,803	28,669
Additional shares for stock-based compensation plans									73	70	84
Average common shares outstanding - diluted (in shares)	30,521	30,429	29,394	28,970	28,940	28,815	28,791	28,803	29,859	28,873	28,753
Earnings from continuing operations per share of common stock:
Basic (in dollars per share)	$ 1.26	$ (0.61)	$ 0.07	$ 1.50	$ 1.27	$ (0.39)	$ (0.01)	$ 1.46	$ 2.19	$ 2.34	$ 2.51
Diluted (in dollars per share)	1.26	(0.61)	0.07	1.50	1.27	(0.39)	(0.01)	1.46	2.19	2.33	2.51
Loss from discontinued operations per share of common stock:
Basic (in dollars per share)	(0.05)	(0.02)	(0.03)	(0.01)	(0.03)	(0.02)	(0.02)	(0.02)	(0.12)	(0.10)	(4.45)
Diluted (in dollars per share)	(0.05)	(0.02)	(0.03)	(0.01)	(0.03)	(0.02)	(0.02)	(0.02)	(0.12)	(0.09)	(4.44)
Earnings (loss) per share of common stock
Basic (in dollars per share)	1.21	(0.63)	0.04	1.49	1.24	(0.41)	(0.03)	1.44	2.07	2.24	(1.94)
Diluted (in dollars per share)	$ 1.20	$ (0.63)	$ 0.04	$ 1.49	$ 1.24	$ (0.41)	$ (0.03)	$ 1.44	$ 2.07	$ 2.24	$ (1.93)
Antidilutive shares									0	2	13
Discontinued Operations, Held-for-sale [Member] | Gill Ranch [Member]
Income Statement [Line Items]
Loss from discontinued operations, net of tax									$ (3,576)	$ (2,742)	$ (127,696)
Loss from discontinued operations per share of common stock:
Basic (in dollars per share)									$ (0.12)	$ (0.10)	$ (4.45)
Diluted (in dollars per share)									$ (0.12)	$ (0.09)	$ (4.44)

Segment Information - Narrative

Segment Information - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Segment Reporting Information [Line Items]
Assets	$ 3,428,454	$ 3,242,662
Operating Segments [Member]
Segment Reporting Information [Line Items]
Number of Reportable Segments	1
Operating Segments [Member] | Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Assets	$ 3,273,835	$ 3,141,969	$ 2,961,326
Northwest Holdings and Northwest Natural [Member] | Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Percent Of Pre Tax Income From Gas Storage Retained When The Costs Of The Capacity Are Not In Utility Rates	80.00%
Percent Of Pre Tax Income From Gas Storage Retained When The Costs Of The Capacity Are In Utility Rates	10.00%
Percent Of Pre Tax Income From Gas Storage Credited To Deferred Regulatory Account	20.00%
Percent Of Pre Tax Income From Gas Storage Credited To Deferred Regulatory Account When In Rates	90.00%
Northwest Holdings and Northwest Natural [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment Reporting, Disclosure of Major Customers	No
Customer Total [Member] | Geographic Concentration Risk [Member] | Oregon [Member] | Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Concentration Risk, Percentage	89.00%
Customer Total [Member] | Geographic Concentration Risk [Member] | Washington [Member] | Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Concentration Risk, Percentage	11.00%
Volumes Delivered [Member] | Residential and Commerical Customers [Member] | Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Concentration Risk, Percentage	60.00%
Gross Profit Margin [Member] | Residential and Commerical Customers [Member] | Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Concentration Risk, Percentage	90.00%

Segment Information - Schedule

Segment Information - Schedule of Summarized Financial Information by Segment (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Operating revenues	$ 247,274	$ 90,317	$ 123,433	$ 285,348	$ 226,702	$ 91,239	$ 124,567	$ 263,635	$ 746,372	$ 706,143	$ 755,038
Depreciation and amortization									91,496	85,156	81,053
Income from operations									143,474	132,162	150,902
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	38,348	(18,506)	2,051	43,418	36,783	(11,144)	(339)	42,011	65,311	67,311	72,073
Capital expenditures									223,471	214,636	213,325
Total assets	3,428,454				3,242,662				3,428,454	3,242,662
Discontinued operations - current assets	15,134				13,269				15,134	13,269
Discontinued operations - total assets					13,300					13,300	13,900
Other Northwest Natural [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues									19,416	24,923	22,096
Depreciation and amortization									990	1,254	1,290
Income from operations									11,428	15,004	12,472
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent									8,146	10,558	11,211
Capital expenditures									1,500	2,005	1,653
Total assets	47,652				50,767				47,652	50,767	50,471
Income Tax Expense (Benefit)											4,000
Northwest Natural Gas Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues									739,944	705,571	755,038
Depreciation and amortization									90,405	84,986	81,024
Income from operations									147,346	133,099	150,922
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent									68,974	68,049	71,720
Capital expenditures									221,380	214,328	213,325
Total assets	3,321,487				3,192,736				3,321,487	3,192,736	3,011,797
Northwest Holdings Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues									6,428	572	0
Depreciation and amortization									1,091	170	29
Income from operations									(3,872)	(937)	(20)
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent									(3,663)	(738)	353
Capital expenditures									2,091	308	0
Total assets	91,833				36,657				91,833	36,657	14,075
Income Tax Expense (Benefit)											400
Natural Gas Distribution [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues									720,528	680,648	732,942
Depreciation and amortization									89,415	83,732	79,734
Income from operations									135,918	118,095	138,450
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent									60,828	57,491	60,509
Capital expenditures									219,880	212,323	211,672
Total assets	3,273,835				3,141,969				3,273,835	3,141,969	2,961,326
Income Tax Expense (Benefit)											1,000
Northwest Natural Gas Company [Member]
Segment Reporting Information [Line Items]
Operating revenues	245,264	$ 87,592	$ 122,242	$ 284,846	226,146	91,227	124,563	263,635	739,944	705,571	755,038
Depreciation and amortization									90,405	84,986	81,024
Income from operations									147,346	133,099	150,922
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent					37,581	$ (11,275)	$ (271)	$ 42,014	68,974	68,049	71,720
Capital expenditures									221,380	214,328	213,325
Total assets	3,321,487				3,192,736				3,321,487	3,192,736
Northwest Natural Gas Company [Member] | Other Northwest Natural [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues									19,416	24,923
Northwest Natural Gas Company [Member] | Northwest Natural Gas Company [Member]
Segment Reporting Information [Line Items]
Operating revenues									739,944	705,571
Northwest Natural Gas Company [Member] | Natural Gas Distribution [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues									720,528	680,648
Northwest Natural Gas Company [Member]
Segment Reporting Information [Line Items]
Discontinued operations - total assets											31,900
Parent Company [Member]
Segment Reporting Information [Line Items]
Operating revenues									746,372	706,143	755,038
Depreciation and amortization									91,496	85,156	81,053
Income from operations									143,474	132,162	150,902
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent									65,311	67,311	72,073
Capital expenditures									223,471	214,636	213,325
Total assets	$ 3,413,320				$ 3,229,393				$ 3,413,320	$ 3,229,393	$ 3,025,872

Segment Information - Additiona

Segment Information - Additional Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Operating revenues	$ 247,274	$ 90,317	$ 123,433	$ 285,348	$ 226,702	$ 91,239	$ 124,567	$ 263,635	$ 746,372	$ 706,143	$ 755,038
Cost of gas									254,911	255,519	324,795
Environmental remediation									12,337	11,127	15,291
Operating Segments [Member] | Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Operating revenues									720,528	680,648	732,942
Cost of gas									255,135	255,743	325,019
Environmental remediation									12,337	11,127	15,291
Revenue taxes									30,325	30,082	0
NGD margin									$ 422,731	$ 383,696	$ 392,632

Common Stock - Narrative (Detai

Common Stock - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2019	Jun. 07, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Authorized (in shares)		100,000,000		100,000,000
Equity Issuance	1,437,500
Shares Issued, Price Per Share			$ 67
Issuance of common stock, net of issuance costs	$ 93,000	$ 92,956
Restated Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number		10,938		55,938	91,688,000	180,163,000
Stock Repurchase Plan [Member]
Stock Repurchase Program
Stock Repurchase Program, Number of Shares Authorized to be Repurchased		2,800,000
Stock Repurchase Program, Authorized Amount		$ 100,000
Treasury Stock, Shares, Acquired		0
Repurchases Since Plan Inception in Year 2000 [Member] | Stock Repurchase Plan [Member]
Stock Repurchase Program
Treasury Stock, Shares, Acquired		2,100,000
Treasury Stock, Value, Acquired, Cost Method		$ 83,300
Northwest Holdings [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reserved Shares Dividend Reinvestment		340,133
Northwest Holdings [Member] | Employee Stock Purchase Plan Member [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock, Capital Shares Reserved for Future Issuance		206,560

Common Stock - Schedule of Summ

Common Stock - Schedule of Summary of Changes in Common Stock (Details) - shares	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Increase (Decrease) in Common Stock [Roll Forward]
Beginning Balance	28,880,000	28,880,000
Equity Issuance	1,437,500
Ending Balance		30,472,000	28,880,000
Common Stock [Member]
Increase (Decrease) in Common Stock [Roll Forward]
Beginning Balance	28,880,000	28,880,000	28,736,000	28,630,000
Sales to employees under ESPP		18,000	19,000	18,000
Stock-based compensation		83,000	64,000	88,000
Equity Issuance		1,438,000
Stock Issued During Period, Shares, Dividend Reinvestment Plan		53,000	61,000
Ending Balance		30,472,000	28,880,000	28,736,000

Revenue - Disaggregation of Rev

Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									$ 755,987	$ 696,157
Operating revenues	$ 247,274	$ 90,317	$ 123,433	$ 285,348	$ 226,702	$ 91,239	$ 124,567	$ 263,635	746,372	706,143	$ 755,038
Operating Lease, Lease Income									171
Natural Gas Distribution [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									729,296	670,662
Gas Storage Revenue, Net of Regulatory Sharing [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									10,240	10,780
Asset Management Revenue, Net of Regulatory Sharing [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									3,705	8,548
Appliance Center Revenue [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									5,471	5,595
Other revenue [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									7,275	572
Alternative revenue [Member]
Disaggregation of Revenue [Line Items]
Operating revenues									(20,984)	8,989
Leasing revenue [Member]
Disaggregation of Revenue [Line Items]
Operating Lease, Lease Income									11,369	997
Operating Segments [Member] | Northwest Natural Gas Company [Member]
Disaggregation of Revenue [Line Items]
Operating revenues									739,944	705,571	755,038
Operating Segments [Member] | Natural Gas Distribution [Member]
Disaggregation of Revenue [Line Items]
Operating revenues									720,528	680,648	732,942
Corporate, Non-Segment [Member] | Other Northwest Natural [Member]
Disaggregation of Revenue [Line Items]
Operating revenues									19,416	24,923	22,096
Corporate, Non-Segment [Member] | Northwest Holdings Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									6,428	572
Operating revenues									6,428	572	0
Corporate, Non-Segment [Member] | Northwest Holdings Other [Member] | Natural Gas Distribution [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									0	0
Corporate, Non-Segment [Member] | Northwest Holdings Other [Member] | Gas Storage Revenue, Net of Regulatory Sharing [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									0	0
Corporate, Non-Segment [Member] | Northwest Holdings Other [Member] | Asset Management Revenue, Net of Regulatory Sharing [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									0	0
Corporate, Non-Segment [Member] | Northwest Holdings Other [Member] | Appliance Center Revenue [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									0	0
Corporate, Non-Segment [Member] | Northwest Holdings Other [Member] | Other revenue [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									6,428	572
Corporate, Non-Segment [Member] | Northwest Holdings Other [Member] | Alternative revenue [Member]
Disaggregation of Revenue [Line Items]
Operating revenues									0	0
Corporate, Non-Segment [Member] | Northwest Holdings Other [Member] | Leasing revenue [Member]
Disaggregation of Revenue [Line Items]
Operating Lease, Lease Income									0	0
Northwest Natural Gas Company [Member]
Disaggregation of Revenue [Line Items]
Operating revenues	$ 245,264	$ 87,592	$ 122,242	$ 284,846	$ 226,146	$ 91,227	$ 124,563	$ 263,635	739,944	705,571	$ 755,038
Northwest Natural Gas Company [Member] | Northwest Natural Gas Company [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									749,559	695,585
Operating revenues									739,944	705,571
Northwest Natural Gas Company [Member] | Northwest Natural Gas Company [Member] | Natural Gas Distribution [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									729,296	670,662
Northwest Natural Gas Company [Member] | Northwest Natural Gas Company [Member] | Gas Storage Revenue, Net of Regulatory Sharing [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									10,240	10,780
Northwest Natural Gas Company [Member] | Northwest Natural Gas Company [Member] | Asset Management Revenue, Net of Regulatory Sharing [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									3,705	8,548
Northwest Natural Gas Company [Member] | Northwest Natural Gas Company [Member] | Appliance Center Revenue [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									5,471	5,595
Northwest Natural Gas Company [Member] | Northwest Natural Gas Company [Member] | Other revenue [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									847	0
Northwest Natural Gas Company [Member] | Northwest Natural Gas Company [Member] | Alternative revenue [Member]
Disaggregation of Revenue [Line Items]
Operating revenues									(20,984)	8,989
Northwest Natural Gas Company [Member] | Northwest Natural Gas Company [Member] | Leasing revenue [Member]
Disaggregation of Revenue [Line Items]
Operating Lease, Lease Income									11,369	997
Northwest Natural Gas Company [Member] | Operating Segments [Member] | Natural Gas Distribution [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									730,143	670,662
Operating revenues									720,528	680,648
Northwest Natural Gas Company [Member] | Operating Segments [Member] | Natural Gas Distribution [Member] | Natural Gas Distribution [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									729,296	670,662
Northwest Natural Gas Company [Member] | Operating Segments [Member] | Natural Gas Distribution [Member] | Gas Storage Revenue, Net of Regulatory Sharing [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0
Northwest Natural Gas Company [Member] | Operating Segments [Member] | Natural Gas Distribution [Member] | Asset Management Revenue, Net of Regulatory Sharing [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0
Northwest Natural Gas Company [Member] | Operating Segments [Member] | Natural Gas Distribution [Member] | Appliance Center Revenue [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0
Northwest Natural Gas Company [Member] | Operating Segments [Member] | Natural Gas Distribution [Member] | Other revenue [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									847	0
Northwest Natural Gas Company [Member] | Operating Segments [Member] | Natural Gas Distribution [Member] | Alternative revenue [Member]
Disaggregation of Revenue [Line Items]
Operating revenues									(20,984)	8,989
Northwest Natural Gas Company [Member] | Operating Segments [Member] | Natural Gas Distribution [Member] | Leasing revenue [Member]
Disaggregation of Revenue [Line Items]
Operating Lease, Lease Income									11,369	997
Northwest Natural Gas Company [Member] | Corporate, Non-Segment [Member] | Other Northwest Natural [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									19,416	24,923
Operating revenues									19,416	24,923
Northwest Natural Gas Company [Member] | Corporate, Non-Segment [Member] | Other Northwest Natural [Member] | Natural Gas Distribution [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									0	0
Northwest Natural Gas Company [Member] | Corporate, Non-Segment [Member] | Other Northwest Natural [Member] | Gas Storage Revenue, Net of Regulatory Sharing [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									10,240	10,780
Northwest Natural Gas Company [Member] | Corporate, Non-Segment [Member] | Other Northwest Natural [Member] | Asset Management Revenue, Net of Regulatory Sharing [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									3,705	8,548
Northwest Natural Gas Company [Member] | Corporate, Non-Segment [Member] | Other Northwest Natural [Member] | Appliance Center Revenue [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									5,471	5,595
Northwest Natural Gas Company [Member] | Corporate, Non-Segment [Member] | Other Northwest Natural [Member] | Other revenue [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax									0	0
Northwest Natural Gas Company [Member] | Corporate, Non-Segment [Member] | Other Northwest Natural [Member] | Alternative revenue [Member]
Disaggregation of Revenue [Line Items]
Operating revenues									0	0
Northwest Natural Gas Company [Member] | Corporate, Non-Segment [Member] | Other Northwest Natural [Member] | Leasing revenue [Member]
Disaggregation of Revenue [Line Items]
Operating Lease, Lease Income									$ 0	$ 0

Revenue - Revenue, Remaining Pe

Revenue - Revenue, Remaining Performance Obligation (Details) $ in Millions	Dec. 31, 2019USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Lessor, Sales-type Lease, Term of Contract	30 years
Lessor, Sales-type Lease, Renewal Term	50 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 16
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Year	2020
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 18.2
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Year	2021
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 14.5
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Year	2022
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 11.6
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Year	2023
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 5.3
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Year	2024
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 73.4

Leases - Lease Revenue (Details

Leases - Lease Revenue (Details)	12 Months Ended
	Dec. 31, 2019USD ($)
Lessor, Lease, Description [Line Items]
Lessor, Sales-type Lease, Term of Contract	30 years
Lessor, Sales-type Lease, Renewal Term	50 years
Residual Value of Leased Asset	$ 4,000,000
Lease Revenue [Abstract]
Operating Lease, Lease Income	171,000
Sales-type Lease, Lease Income	11,198,000
Lease Income	11,369,000
Operating Leases Payment to be Received [Abstract]
Lessor, Operating Lease, Payments to be Received, Next Twelve Months	65,000
Lessor, Operating Lease, Payments to be Received, Two Years	49,000
Lessor, Operating Lease, Payments to be Received, Three Years	45,000
Lessor, Operating Lease, Payments to be Received, Four Years	45,000
Lessor, Operating Lease, Payments to be Received, Five Years	45,000
Lessor, Operating Lease, Payments to be Received, Thereafter	93,000
Lessor, Operating Lease, Payments to be Received	342,000
Total Lease Payments to be Received [Abstract]
Lease Payments to be Received, Next twelve months	18,293,000
Lease Payments to be Received, Two Years	17,567,000
Lease Payments to be Received, Three Years	17,071,000
Lease Payments to be Received, Four Years	16,602,000
Lease Payments to be Received, Five Years	15,912,000
Lease Payments to be Received, Thereafter	264,833,000
Lease Payments to be Received	350,278,000
Non-utility Property Rentals [Member]
Operating Leases Payment to be Received [Abstract]
Lessor, Operating Lease, Payments to be Received, Next Twelve Months	500,000
Lessor, Operating Lease, Payments to be Received, Two Years	500,000
Lessor, Operating Lease, Payments to be Received, Three Years	$ 500,000
Compressed Natural Gas Lease [Member]
Lessor, Lease, Description [Line Items]
Lessor, Sales-type Lease, Term of Contract	10 years
North Mist Lease [Member]
Lessor, Lease, Description [Line Items]
Variable Lease, Payment	$ 0
Residual Value of Leased Asset	0
Sales-type Lease [Member]
Sales-type Leases Payments to be Received [Abstract]
Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Next Twelve Months	18,228,000
Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Two Years	17,518,000
Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Three Years	17,026,000
Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Four Years	16,557,000
Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Five Years	15,867,000
Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Thereafter	264,740,000
Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received	349,936,000
Receivable with Imputed Interest, Discount	202,319,000
Receivable with Imputed Interest, Net Amount	147,617,000
Other Nonoperating Income (Expense) [Member]
Lease Revenue [Abstract]
Lease Income	$ 500,000

Leases - Lease Expense (Details

Leases - Lease Expense (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Lessee, Lease, Description [Line Items]
Operating Lease, Expense	$ 4,811
Short-term Lease, Cost	$ 1,146
Minimum [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Term of Contract	1 year
Maximum [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Term of Contract	11 years
Northwest Natural Gas Company [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Expense	$ 4,620
Short-term Lease, Cost	1,146
Other Northwest Holdings [Member] | Corporate, Non-Segment [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Expense	191
Short-term Lease, Cost	$ 0
New Headquarters Lease Renewal Term 1 of 2 [Member] | New Headquarters Lease [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Lease Not yet Commenced, Renewal Term	7 years

Leases - Lease Asset and Liabil

Leases - Lease Asset and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Lease Asset and Liabilities [Abstract]
Operating Lease, Right-of-Use Asset	$ 2,950	$ 0
Operating Lease, Liability, Current	2,101	0
Operating Lease, Liability, Noncurrent	841	0
Operating Lease, Liability	2,942
Maturity of Operating Lease Liabilities [Abstract]
Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months	2,155
Lessee, Operating Lease, Liability, Payments, Due Year Two	195
Lessee, Operating Lease, Liability, Payments, Due Year Three	129
Lessee, Operating Lease, Liability, Payments, Due Year Four	88
Lessee, Operating Lease, Liability, Payments, Due Year Five	89
Lessee, Operating Lease, Liability, Payments, Due after Year Five	526
Lessee, Operating Lease, Liability, Payments, Due	3,182
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	240
Operating Lease, Liability	2,942
Operating Lease, Liability, Current	2,101	0
Operating Lease, Liability, Noncurrent	841	0
Lease Not Yet Commenced [Abstract]
Lessee, Operating Lease, Liability, Payments, Due	3,182
Leases Cash Flow [Abstract]
Operating Lease, Payments	4,629
Finance Lease, Principal Payments	120
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	7,577
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability	312
Finance Leases [Abstract]
Finance Lease, Right-of-Use Asset	500
Prior Period Disclosures [Abstract]
Operating Leases, Rent Expense		5,900	$ 7,300	$ 5,900
Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months	2,155
Lessee, Operating Lease, Liability, Payments, Due Year Two	195
Lessee, Operating Lease, Liability, Payments, Due Year Three	129
Lessee, Operating Lease, Liability, Payments, Due Year Four	88
Lessee, Operating Lease, Liability, Payments, Due Year Five	89
Lessee, Operating Lease, Liability, Payments, Due after Year Five	526
Lessee, Operating Lease, Liability, Payments, Due	3,182
Northwest Natural Gas Company [Member]
Operating Lease Asset and Liabilities [Abstract]
Operating Lease, Right-of-Use Asset	2,760	0
Operating Lease, Liability, Current	1,979	0
Operating Lease, Liability, Noncurrent	772	0
Operating Lease, Liability	$ 2,751
Operating Lease, Weighted Average Discount Rate, Percent	3.98%
Maturity of Operating Lease Liabilities [Abstract]
Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months	$ 2,029	5,368
Lessee, Operating Lease, Liability, Payments, Due Year Two	143	4,812
Lessee, Operating Lease, Liability, Payments, Due Year Three	111	7,077
Lessee, Operating Lease, Liability, Payments, Due Year Four	88	7,223
Lessee, Operating Lease, Liability, Payments, Due Year Five	89	7,304
Lessee, Operating Lease, Liability, Payments, Due after Year Five	526	149,881
Lessee, Operating Lease, Liability, Payments, Due	2,986	181,665
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	235
Operating Lease, Liability	2,751
Operating Lease, Liability, Current	1,979	0
Operating Lease, Liability, Noncurrent	772	0
Lease Not Yet Commenced [Abstract]
Lessee, Operating Lease, Liability, Payments, Due	2,986	181,665
Leases Cash Flow [Abstract]
Operating Lease, Payments	4,447
Finance Lease, Principal Payments	120
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	7,205
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability	312
Prior Period Disclosures [Abstract]
Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months	2,029	5,368
Lessee, Operating Lease, Liability, Payments, Due Year Two	143	4,812
Lessee, Operating Lease, Liability, Payments, Due Year Three	111	7,077
Lessee, Operating Lease, Liability, Payments, Due Year Four	88	7,223
Lessee, Operating Lease, Liability, Payments, Due Year Five	89	7,304
Lessee, Operating Lease, Liability, Payments, Due after Year Five	526	149,881
Lessee, Operating Lease, Liability, Payments, Due	2,986	$ 181,665
Corporate, Non-Segment [Member] | Other Northwest Holdings [Member]
Operating Lease Asset and Liabilities [Abstract]
Operating Lease, Right-of-Use Asset	190
Operating Lease, Liability, Current	122
Operating Lease, Liability, Noncurrent	69
Operating Lease, Liability	191
Maturity of Operating Lease Liabilities [Abstract]
Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months	126
Lessee, Operating Lease, Liability, Payments, Due Year Two	52
Lessee, Operating Lease, Liability, Payments, Due Year Three	18
Lessee, Operating Lease, Liability, Payments, Due Year Four	0
Lessee, Operating Lease, Liability, Payments, Due Year Five	0
Lessee, Operating Lease, Liability, Payments, Due after Year Five	0
Lessee, Operating Lease, Liability, Payments, Due	196
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	5
Operating Lease, Liability	191
Operating Lease, Liability, Current	122
Operating Lease, Liability, Noncurrent	69
Lease Not Yet Commenced [Abstract]
Lessee, Operating Lease, Liability, Payments, Due	196
Leases Cash Flow [Abstract]
Operating Lease, Payments	182
Finance Lease, Principal Payments	0
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	372
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability	0
Prior Period Disclosures [Abstract]
Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months	126
Lessee, Operating Lease, Liability, Payments, Due Year Two	52
Lessee, Operating Lease, Liability, Payments, Due Year Three	18
Lessee, Operating Lease, Liability, Payments, Due Year Four	0
Lessee, Operating Lease, Liability, Payments, Due Year Five	0
Lessee, Operating Lease, Liability, Payments, Due after Year Five	0
Lessee, Operating Lease, Liability, Payments, Due	$ 196
Maximum [Member] | Northwest Natural Gas Company [Member]
Operating Lease Asset and Liabilities [Abstract]
Operating Lease, Weighted Average Remaining Lease Term	1 year
New Headquarters Lease [Member]
Maturity of Operating Lease Liabilities [Abstract]
Lessee, Operating Lease, Liability, Payments, Due	$ 160,000
Lease Not Yet Commenced [Abstract]
Lessee, Operating Lease, Lease Not yet Commenced, Term of Contract	20 years
Lessee, Operating Lease, Liability, Payments, Due	$ 160,000
Prior Period Disclosures [Abstract]
Lessee, Operating Lease, Liability, Payments, Due	$ 160,000
New Headquarters Lease Renewal Term 1 of 2 [Member] | New Headquarters Lease [Member]
Lease Not Yet Commenced [Abstract]
Lessee, Operating Lease, Lease Not yet Commenced, Renewal Term	7 years

Debt (Details)

Debt (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Short-term Debt, Other Disclosures [Abstract]
Short-term debt	$ 149,100,000	$ 217,620,000
Short-term Debt, Weighted Average Interest Rate, at Point in Time	2.00%	3.00%
Commercial Paper, Maximum Maturity	22 days
Commercial Paper, Average Maturity	10 days
Credit Agreements [Abstract]
Letters of Credit Outstanding, Amount	$ 1,000,000	$ 2,800,000
Broker-Dealer, Bank Loan, Short-term	0	0
Debt Instruments [Abstract]
Long-term Debt, Gross	$ 886,776,000	741,813,000
Ratio of Indebtedness to Net Capital	0.543
Liabilities, Fair Value Disclosure [Abstract]
Long-term Debt, Gross	$ 886,776,000	741,813,000
Unamortized Debt Issuance Expense	5,712,000	5,577,000
Long-term Debt	881,064,000	736,236,000
Debt Instrument, Fair Value Disclosure	957,268,000	762,335,000
Line of Credit [Member]
Credit Agreements [Abstract]
Line of Credit Facility, Maximum Borrowing Capacity	100,000,000
Line of Credit Facility Contingent Increase To Maximum Borrowing Capacity	$ 150,000,000
Debt Instrument Covenant Consolidated Indebtedness To Capitalization Ratio	70.00%
Line of Credit Facility, Amount Outstanding	$ 24,000,000	0
Letter of Credit [Member]
Credit Agreements [Abstract]
Line of Credit Facility, Maximum Borrowing Capacity	40,000,000
Letters of Credit Outstanding, Amount	0	0
Northwest Natural Gas Company [Member]
Short-term Debt, Other Disclosures [Abstract]
Short-term debt	$ 125,100,000	$ 217,500,000
Short-term Debt, Weighted Average Interest Rate, at Point in Time	2.00%	3.00%
Maturities of Long-term Debt [Abstract]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 75,000,000
Long-term Debt, Maturities, Repayments of Principal in Year Two	60,000,000
Long-term Debt, Maturities, Repayments of Principal in Year Three	0
Long-term Debt, Maturities, Repayments of Principal in Year Four	90,000,000
Long-term Debt, Maturities, Repayments of Principal in Year Five	0
Long-term Debt, Maturities, Repayments of Principal after Year Five	624,700,000
Debt Instruments [Abstract]
Long-term Debt, Gross	849,700,000	$ 739,700,000
Long-Term Debt, Current Maturities, Gross	75,000,000	30,000,000
Long-term Debt, Excluding Current Maturities, Gross	774,700,000	709,700,000
Debt Outstanding
Proceeds from Issuance of Debt	140,000,000
Liabilities, Fair Value Disclosure [Abstract]
Long-term Debt, Gross	849,700,000	739,700,000
Unamortized Debt Issuance Expense	5,712,000	5,577,000
Long-term Debt	843,988,000	734,123,000
Debt Instrument, Fair Value Disclosure	$ 919,835,000	760,222,000
Northwest Natural Gas Company [Member] | Note 1545 Series Due 2018 [Member]
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	1.545%
Repayments of Long-term Debt [Abstract]
Extinguishment of Debt, Amount	$ 75,000,000
Northwest Natural Gas Company [Member] | Note 6600 Series B Due 2018 [Member]
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	6.60%
Repayments of Long-term Debt [Abstract]
Extinguishment of Debt, Amount	$ 22,000,000
Northwest Natural Gas Company [Member] | 8.310% Series due 2019
Debt Instruments [Abstract]
Secured Debt	$ 0	$ 10,000,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	8.31%	8.31%
Repayments of Long-term Debt [Abstract]
Extinguishment of Debt, Amount	$ 10,000,000
Northwest Natural Gas Company [Member] | 7.630% Series due 2019
Debt Instruments [Abstract]
Secured Debt	$ 0	$ 20,000,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	7.63%	7.63%
Repayments of Long-term Debt [Abstract]
Extinguishment of Debt, Amount	$ 20,000,000
Northwest Natural Gas Company [Member] | 5.370% Series due 2020
Debt Instruments [Abstract]
Secured Debt	$ 75,000,000	$ 75,000,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	5.37%	5.37%
Northwest Natural Gas Company [Member] | 9.050% Series due 2021
Debt Instruments [Abstract]
Secured Debt	$ 10,000,000	$ 10,000,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	9.05%	9.05%
Northwest Natural Gas Company [Member] | 3.176% Series due 2021
Debt Instruments [Abstract]
Secured Debt	$ 50,000,000	$ 50,000,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	3.18%	3.18%
Northwest Natural Gas Company [Member] | 3.542% Series due 2023
Debt Instruments [Abstract]
Secured Debt	$ 50,000,000	$ 50,000,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	3.54%	3.54%
Northwest Natural Gas Company [Member] | 7.720% Series due 2025
Debt Instruments [Abstract]
Secured Debt	$ 20,000,000	$ 20,000,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	7.72%	7.72%
Northwest Natural Gas Company [Member] | 5.620% Series due 2023
Debt Instruments [Abstract]
Secured Debt	$ 40,000,000	$ 40,000,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	5.62%	5.62%
Northwest Natural Gas Company [Member] | 6.520% Series due 2025
Debt Instruments [Abstract]
Secured Debt	$ 10,000,000	$ 10,000,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	6.52%	6.52%
Northwest Natural Gas Company [Member] | 7.050% Series due 2026
Debt Instruments [Abstract]
Secured Debt	$ 20,000,000	$ 20,000,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	7.05%	7.05%
Northwest Natural Gas Company [Member] | 3.211% Series due 2026
Debt Instruments [Abstract]
Secured Debt	$ 35,000,000	$ 35,000,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	3.21%	3.21%
Northwest Natural Gas Company [Member] | 7.000% Series due 2027
Debt Instruments [Abstract]
Secured Debt	$ 20,000,000	$ 20,000,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	7.00%	7.00%
Northwest Natural Gas Company [Member] | 2.822% Series due 2027
Debt Instruments [Abstract]
Secured Debt	$ 25,000,000	$ 25,000,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	2.82%	2.82%
Northwest Natural Gas Company [Member] | 6.650% Series due 2027
Debt Instruments [Abstract]
Secured Debt	$ 19,700,000	$ 19,700,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	6.65%	6.65%
Northwest Natural Gas Company [Member] | 6.650% Series due 2028
Debt Instruments [Abstract]
Secured Debt	$ 10,000,000	$ 10,000,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	6.65%	6.65%
Northwest Natural Gas Company [Member] | 3.141% Series due 2029
Debt Instruments [Abstract]
Secured Debt	$ 50,000,000	$ 0
Debt Outstanding
Proceeds from Issuance of Debt	$ 50,000,000
Debt Instrument, Interest Rate, Stated Percentage	3.141%
Northwest Natural Gas Company [Member] | 7.740% Series due 2030
Debt Instruments [Abstract]
Secured Debt	$ 20,000,000	$ 20,000,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	7.74%	7.74%
Northwest Natural Gas Company [Member] | 7.850% Series due 2030
Debt Instruments [Abstract]
Secured Debt	$ 10,000,000	$ 10,000,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	7.85%	7.85%
Northwest Natural Gas Company [Member] | 5.820% Series due 2032
Debt Instruments [Abstract]
Secured Debt	$ 30,000,000	$ 30,000,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	5.82%	5.82%
Northwest Natural Gas Company [Member] | 5.660% Series due 2033
Debt Instruments [Abstract]
Secured Debt	$ 40,000,000	$ 40,000,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	5.66%	5.66%
Northwest Natural Gas Company [Member] | 5.250% Series due 2035
Debt Instruments [Abstract]
Secured Debt	$ 10,000,000	$ 10,000,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	5.25%	5.25%
Northwest Natural Gas Company [Member] | 4.000% Series due 2042
Debt Instruments [Abstract]
Secured Debt	$ 50,000,000	$ 50,000,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	4.00%	4.00%
Northwest Natural Gas Company [Member] | 4.136% Series due 2046
Debt Instruments [Abstract]
Secured Debt	$ 40,000,000	$ 40,000,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	4.14%	4.14%
Northwest Natural Gas Company [Member] | 3.685% Series due 2047
Debt Instruments [Abstract]
Secured Debt	$ 75,000,000	$ 75,000,000
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	3.69%	3.69%
Northwest Natural Gas Company [Member] | 4.110% Series due 2048
Debt Instruments [Abstract]
Secured Debt	$ 50,000,000	$ 50,000,000
Debt Outstanding
Proceeds from Issuance of Debt		$ 50,000,000
Debt Instrument, Interest Rate, Stated Percentage	4.11%	4.11%
Northwest Natural Gas Company [Member] | 3.869% Series due 2049
Debt Instruments [Abstract]
Secured Debt	$ 90,000,000	$ 0
Debt Outstanding
Proceeds from Issuance of Debt	$ 90,000,000
Debt Instrument, Interest Rate, Stated Percentage	3.869%
Northwest Natural Gas Company [Member] | Line of Credit [Member]
Credit Agreements [Abstract]
Line of Credit Facility, Maximum Borrowing Capacity	$ 300,000,000
Line of Credit Facility Contingent Increase To Maximum Borrowing Capacity	$ 450,000,000
Debt Instrument Covenant Consolidated Indebtedness To Capitalization Ratio	70.00%
Line of Credit Facility, Amount Outstanding	$ 0	0
Northwest Natural Gas Company [Member] | Letter of Credit [Member]
Credit Agreements [Abstract]
Line of Credit Facility, Maximum Borrowing Capacity	60,000,000
Letters of Credit Outstanding, Amount	$ 0	$ 0
Other Northwest Holdings [Member] | Corporate, Non-Segment [Member] | NWN Water Term Loan Due 2021 [Member]
Credit Agreements [Abstract]
Debt Instrument Covenant Consolidated Indebtedness To Capitalization Ratio	70.00%
Debt Outstanding
Debt Instrument, Interest Rate, Stated Percentage	2.35%
Liabilities, Fair Value Disclosure [Abstract]
Long-term Debt	$ 35,000,000

Stock-Based Compensation - Long

Stock-Based Compensation - Long Term Incentive Plan (Details) - Long Term Incentive Plan [Member] - USD ($)	12 Months Ended			24 Months Ended	36 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	1,100,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant, Any Award Type	510,931
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	0	0		0	0
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	79,733	82,680	84,522	82,680	82,680	84,522	89,973
Performance Shares [Abstract]
Share-based Payment Arrangement, Expense	$ 1,800,000	$ 1,800,000	$ 1,600,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount	$ 3,400,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	$ 61.17	$ 56.47	$ 53.90	$ 56.47	$ 56.47	$ 53.90	$ 48.85
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value	$ 54.22	$ 50.75	$ 47.07
Restricted Stock Units [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	4 years
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	(35,778)	(32,689)	(35,341)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	36,018	32,450	32,168
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 65.29	$ 57.59	$ 60.51
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	(3,187)	(1,603)	(2,278)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	$ 63.89	$ 59.95	$ 53.78
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Award Target Share	30,234
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	0
Performance Shares [Abstract]
Share-based Payment Arrangement, Expense	$ 572,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value		$ 57.05		$ 57.05	$ 57.05
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value	$ 57.05
Performance Shares [Member] | A 2019 Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Award Target Share	0
Performance Shares [Abstract]
Share-based Payment Arrangement, Expense	$ 0
Performance Shares [Member] | A 2018 Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Award Target Share	0
Performance Shares [Abstract]
Share-based Payment Arrangement, Expense	$ 0			$ 0
Performance Shares [Member] | A 2017 Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Award Target Share	30,234
Performance Shares [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted	41,573
Share-based Payment Arrangement, Expense	$ 572,000				$ 1,971,000
Performance Shares [Member] | A 2016 Award [Member]
Performance Shares [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted		28,218
Share-based Payment Arrangement, Expense		$ 598,000				$ 1,413,000
Performance Shares [Member] | A 2015 Award [Member]
Performance Shares [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted			18,304
Share-based Payment Arrangement, Expense			$ (346,000)				$ 1,169,000
Maximum [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Award Target Share	60,468
Maximum [Member] | Performance Shares [Member] | A 2019 Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Award Target Share	0
Maximum [Member] | Performance Shares [Member] | A 2018 Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Award Target Share	0
Maximum [Member] | Performance Shares [Member] | A 2017 Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Award Target Share	60,468
Target Achieved [Member] | Performance Shares [Member] | A 2019 Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Award Target Share	35,170
Target Achieved [Member] | Performance Shares [Member] | A 2018 Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Award Target Share	31,825

Stock-Based Compensation - Rest

Stock-Based Compensation - Restated Stock Option Plan (Details) - USD ($)	12 Months Ended			84 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proceeds from stock options exercised	$ 2,015,000	$ 1,546,000	$ 4,819,000
Share-based Payment Arrangement, Expense, Tax Benefit	575,000	659,000	930,000
Restated Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proceeds from stock options exercised	2,000,000
Share-based Payment Arrangement, Expense, Tax Benefit	200,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	$ 300,000	$ 900,000	$ 1,400	$ 300,000	$ 2,800
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price	$ 0	$ 43.29	$ 41,150
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	(45,000)	(35,450)	(88,275,000)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	10,938	55,938	91,688,000	10,938	180,163,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	$ 45.67	$ 44.96	$ 44,430	$ 45.67	$ 44,380
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	10 years 7 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross				0
Share Based Compensation Arrangement By Share Based Payment Award Exchange Period	6 months
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price	$ 44.79	$ 43.61	$ 44,330
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value	$ 1,000,000	$ 800,000	$ 1,800
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period	0	(300)	(200,000)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term	1 year 1 month 13 days

Stock-Based Compensation - Empl

Stock-Based Compensation - Employee Stock Purchase Plan (Details) - Employee Stock Purchase Plan [Member]	12 Months Ended
	Dec. 31, 2019USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent	85.00%
Maximum Value Of Stock Employees Are Allowed To Purchase	$ 21,222

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Expense, Tax Benefit	$ (575)	$ (659)	$ (930)
Share-based Payment Arrangement, Expense, after Tax	1,597	1,830	1,424
Share-based Payment Arrangement, Amount Capitalized	430	531	528
Operations and Maintenance Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Expense	$ 2,172	$ 2,489	$ 2,354

Pension and Other Postretirem_3

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, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Plan [Member]
Reconciliation of change in plan assets:
Fair value of plan assets at January 1	$ 257,797
Fair value of plan assets at December 31	313,051	$ 257,797
Northwest Natural Gas Company [Member] | Other Postretirement Benefits Plan [Member]
Reconciliation of change in benefit obligation:
Obligation at January 1	28,172	28,927
Service cost	244	282
Interest cost	1,117	964
Net actuarial (gain) loss	1,809	(327)
Benefits paid	(1,774)	(1,674)	$ (1,737)
Obligation at December 31	29,568	28,172	28,927
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	1,774	1,674
Benefits paid	(1,774)	(1,674)	(1,737)
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	455,568	486,289
Service cost	6,308	7,185
Interest cost	18,683	16,991
Net actuarial (gain) loss	58,269	(32,979)
Benefits paid	(23,160)	(21,918)	(31,580)
Obligation at December 31	515,668	455,568	486,289
Reconciliation of change in plan assets:
Fair value of plan assets at January 1	257,797	287,925
Actual return on plan assets	65,104	(25,925)
Employer contributions	13,310	17,715
Benefits paid	(23,160)	(21,918)	(31,580)
Fair value of plan assets at December 31	313,051	257,797	$ 287,925
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	(29,568)	(28,172)
Northwest Holdings and Northwest Natural [Member] | Pension Plan [Member]
Reconciliation of change in plan assets:
Defined Benefit Plan, Funded (Unfunded) Status of Plan	$ (202,617)	$ (197,771)

Pension and Other Postretirem_4

Pension and Other Postretirement Benefits Costs - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 22, 2013
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year	6.50%
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	4.75%
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plan Assets, Amount	$ 313,051	$ 257,797
Qualified Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Accumulated Benefit Obligation	434,900	385,900
Non-Qualified Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plan Assets, Amount	0
Defined Benefit Plan, Benefit Obligation	38,300	35,400
Northwest Natural Gas Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan Amounts That Will Be Amortized From Accumulated Other Comprehensive Income Loss In Next Fiscal Year Regulatory	18,300
Defined Benefit Plan Amortization Of Net Gains Losses Regulatory	18,800
Defined Benefit Plan Amortization Of Net Prior Service Cost Credit Regulatory	500
Settlement expense	(900)
Payment for Pension and Other Postretirement Benefits	11,000
Defined Contribution Plan, Cost	7,000	6,500	$ 5,400
Northwest Natural Gas Company [Member] | Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plan Assets, Amount	313,051	257,797	287,925
Total Pension Asset Investments Net Of Receivables And Payables	313,050	257,796
Defined Benefit Plan, Benefit Obligation	515,668	455,568	486,289
Payment for Pension and Other Postretirement Benefits	13,310	17,715
Expected future employer contributions	31,338
Northwest Natural Gas Company [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plan Assets, Amount	0	0	0
Defined Benefit Plan, Benefit Obligation	29,568	28,172	28,927
Payment for Pension and Other Postretirement Benefits	1,774	1,674
Expected future employer contributions	1,756
Northwest Natural Gas Company [Member] | Qualified Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(164,300)
Plan Assets, Amount	313,100	257,800
Defined Benefit Plan, Benefit Obligation	477,300	420,200
Expected future employer contributions	29,000
Northwest Natural Gas Company [Member] | Western States Office and Professional Employees Union Pension Fund [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Multiemployer Plans, Withdrawal Obligation	6,500			$ 8,300
Multiemployer Plans, Plan Contributions	600
Multiemployer Plan, Contributions by Employer	$ 600	$ 600	$ 600
Northwest Natural Gas Company [Member] | Western States Office and Professional Employees Union Pension Fund [Member] | Minimum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Multiemployer Plan, Collective-Bargaining Arrangement, Percentage of Contributions Required for Multiple Collective-Bargaining Arrangements	5.00%
Northwest Natural Gas Company [Member] | Western States Office and Professional Employees Union Pension Fund [Member] | Maximum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Multiemployer Plan, Collective-Bargaining Arrangement, Percentage of Contributions Required for Multiple Collective-Bargaining Arrangements	6.00%

Pension and Other Postretirem_5

Pension and Other Postretirement Benefits Costs - Schedule of Amounts Realized in Other Comprehensive Loss (Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory Asset, Net actuarial loss (gain)	$ 10,424	$ 14,261	$ 12,177
Regulatory Asset, Prior service cost	(7)	(42)	(127)
Regulatory Asset, Actuarial loss	(14,057)	(18,761)	(14,802)
Regulatory Asset, Total	(3,640)	(4,542)	(2,752)
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory Asset, Net actuarial loss (gain)	1,809	(327)	(214)
Regulatory Asset, Prior service cost	468	468	468
Regulatory Asset, Actuarial loss	(369)	(448)	(696)
Regulatory Asset, Total	1,908	(307)	(442)
Qualified Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Amounts reclassified to AOCL	3,595	(677)	2,777
Other Comprehensive Loss (Income), Prior service cost	0	0	0
Loss from plan settlement	(648)	(1,052)	(946)
Total reclassifications before tax	$ 2,947	$ (1,729)	$ 1,831

Pension and Other Postretirem_6

Pension and Other Postretirement Benefits Costs - Schedule of Amount Recognized in AOCL (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Qualified Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
AOCL, Prior Service Costs (Credit)	$ 0	$ 0
AOCL, Net Actuarial Loss	14,484	11,537
AOCL, Total	14,484	11,537
Pension Costs [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory Assets, Prior Service Cost (Credit)	0	7
Regulatory Assets, Net Actuarial Loss	166,903	170,535
Regulatory Assets	166,903	170,542
Postretirement Benefit Costs [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory Assets, Prior Service Cost (Credit)	(1,270)	(1,738)
Regulatory Assets, Net Actuarial Loss	7,629	6,189
Regulatory Assets	$ 6,359	$ 4,451

Pension and Other Postretirem_7

Pension and Other Postretirement Benefits Costs - Schedule of AOCL and Changes in AOCL, Non-Qualified Employee Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ (7,188)
Ending balance	(10,733)	$ (7,188)
Northwest Holdings and Northwest Natural [Member] | Non-Qualified Pension Plans, Defined Benefit [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(7,188)	(8,438)
Amounts reclassified to AOCL	(3,611)	642
Amortization of actuarial losses	648	1,052
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax	1,366	0
Total reclassifications before tax	(4,329)	1,694
Tax expense (benefit)	784	(444)
Total reclassifications for the period	(3,545)	1,250
Ending balance	$ (10,733)	$ (7,188)

Pension and Other Postretirem_8

Pension and Other Postretirement Benefits Costs - Schedule of Pension Plan Target Allocations (Details)	Dec. 31, 2019
Long government/credit [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation, percentage	20.00%
U.S. small/mid cap equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation, percentage	10.00%
Emerging markets equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation, percentage	5.00%
Northwest Natural Gas Company [Member] | U.S. large cap equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation, percentage	18.00%
Northwest Natural Gas Company [Member] | Non-U.S. equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation, percentage	18.00%
Northwest Natural Gas Company [Member] | Absolute Return Strategy Investment Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation, percentage	12.00%
Northwest Natural Gas Company [Member] | Real estate funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation, percentage	7.00%
Northwest Natural Gas Company [Member] | High yield bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation, percentage	5.00%
Northwest Natural Gas Company [Member] | Emerging market debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocation, percentage	5.00%

Pension and Other Postretirem_9

Pension and Other Postretirement Benefits Costs - Schedule of Components of Net Periodic Benefit Cost for NW Natural (Details) - Northwest Natural Gas Company Consolidated [Member] - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 244	$ 282	$ 341
Interest cost		1,116	964	1,141
Expected return on plan assets		0	0	0
Amortization of prior service costs		(468)	(468)	(468)
Amortization of net actuarial loss		368	448	696
Net periodic benefit cost		1,260	1,226	1,710
Amount allocated to construction		(86)	(98)	(587)
Amount deferred to regulatory balancing account		0	0	0
Net periodic benefit cost charged to expense		1,174	1,128	1,123
Regulatory Pension Disallowance		0	0	0
Amortization of Regulatory Balancing Account		0	0	0
Defined Benefit Plan Net Amount Charged To Expense		1,174	1,128	1,123
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		6,308	7,185	7,090
Interest cost		18,684	16,991	18,111
Expected return on plan assets		(20,854)	(20,639)	(20,433)
Amortization of prior service costs		7	43	127
Amortization of net actuarial loss		14,704	19,813	15,748
Net periodic benefit cost		18,849	23,393	20,643
Amount allocated to construction		(2,493)	(2,764)	(6,597)
Amount deferred to regulatory balancing account		0	10,314	6,542
Net periodic benefit cost charged to expense		16,356	10,315	7,504
Regulatory Pension Disallowance	$ 10,500	10,500	0	0
Amortization of Regulatory Balancing Account	12,500	16,841	0	0
Defined Benefit Plan Net Amount Charged To Expense		43,697	10,315	$ 7,504
Operating Expense [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory Pension Disallowance	3,900	6,200	2,400
Other Nonoperating Income (Expense) [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory Pension Disallowance	$ 6,600	$ 10,600	$ 7,900

Pension and Other Postretire_10

Pension and Other Postretirement Benefits Costs - Schedule of Assumptions Used (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Thereafter	3.50%
Other Postretirement Benefits Plan [Member]
Assumptions for net periodic benefit cost:
Weighted-average discount rate	4.13%	3.44%	3.85%
Assumptions for year-end funded status:
Weighted-average discount rate	3.11%	4.13%	3.44%
Pension Plan [Member]
Assumptions for net periodic benefit cost:
Weighted-average discount rate	4.19%	3.51%	3.99%
Expected long-term rate of return	7.50%	7.50%	7.50%
Assumptions for year-end funded status:
Weighted-average discount rate	3.16%	4.20%	3.52%
Expected long-term rate of return	7.25%	7.50%	7.50%
Minimum [Member] | Pension Plan [Member]
Assumptions for net periodic benefit cost:
Rate of Compensation Increase	3.25%	3.25%	3.25%
Assumptions for year-end funded status:
Rate of Compensation Increase	3.50%	3.25%	3.25%
Maximum [Member] | Pension Plan [Member]
Assumptions for net periodic benefit cost:
Rate of Compensation Increase	4.50%	4.50%	4.50%
Assumptions for year-end funded status:
Rate of Compensation Increase	6.50%	4.50%	4.50%

Pension and Other Postretire_11

Pension and Other Postretirement Benefits Costs - Schedule of Effect of One Percentage Point Change in Assumed Health Care Cost (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
1% Increase
Effect on net periodic postretirement health care benefit cost	$ 49
Effect on the accumulated postretirement benefit obligation	710
1% Decrease
Effect on net periodic postretirement health care benefit cost	44
Effect on the accumulated postretirement benefit obligation	$ 640

Pension and Other Postretire_12

Pension and Other Postretirement Benefits Costs - Schedule of Future Employer Contributions and Benefit Payments (Details) - Northwest Natural Gas Company [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Payment for Pension and Other Postretirement Benefits	$ 11,000
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Payment for Pension and Other Postretirement Benefits	13,310	$ 17,715
Expected future employer contributions	31,338
Benefits paid	23,160	21,918	$ 31,580
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2019	23,412
2020	24,304
2021	25,094
2022	25,941
2023	26,757
2024-2028	148,000
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Payment for Pension and Other Postretirement Benefits	1,774	1,674
Expected future employer contributions	1,756
Benefits paid	1,774	$ 1,674	$ 1,737
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2019	1,756
2020	1,833
2021	1,848
2022	1,899
2023	1,903
2024-2028	$ 8,945

Pension and Other Postretire_13

Pension and Other Postretirement Benefits Costs - Schedule of Fair Value of Plan Assets (Details) - Pension Plan [Member] - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	$ 313,051	$ 257,797
Northwest Natural Gas Company [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	313,051	257,797	$ 287,925
Total Pension Asset Investments Net Of Receivables And Payables	313,050	257,796
Accrued interest and dividend income	3,243	1
Due from broker for securities sold	0	0
Total receivables	3,243	1
Due to broker for securities purchased	3,242	0
Northwest Natural Gas Company [Member] | United States Equity [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	95,604	85,233
Northwest Natural Gas Company [Member] | Non-U.S. equity [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	107,505	95,011
Northwest Natural Gas Company [Member] | Liability hedging [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	93,028	45,659
Northwest Natural Gas Company [Member] | Opportunistic [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	9,864	23,186
Northwest Natural Gas Company [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	7,049	8,707
Northwest Natural Gas Company [Member] | Level 1 [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Total Pension Asset Investments Net Of Receivables And Payables	33,168	24,994
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	33,168	24,994
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	0
Northwest Natural Gas Company [Member] | Level 2 [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Total Pension Asset Investments Net Of Receivables And Payables	0	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]
Total Pension Asset Investments Net Of Receivables And Payables	0	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]
Total Pension Asset Investments Net Of Receivables And Payables	279,882	232,802
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	95,604	85,233
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	74,337	70,017
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	93,028	45,659
Northwest Natural Gas Company [Member] | Fair Value Measured at NAV [Member] | Opportunistic [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Plan Assets, Amount	9,864	23,186
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	$ 7,049	$ 8,707

Income Tax (Details)

Income Tax (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 21, 2017
Regulatory Assets [Line Items]
Deferred Tax Rate Differential, Post TCJA				$ 0	$ (76,000)	$ 0
Regulatory Settlement				(1,129,000)	0	0
Deferred Tax Liabilities, Property, Plant and Equipment		$ 269,886,000		269,886,000	288,385,000
Deferred Tax Liabilities, Leasing Arrangements		40,133,000		40,133,000	0
Deferred Tax Liabilities Non Regulated Liabilities		751,000		751,000	1,061,000
Deferred Tax Liabilities, Net		295,643,000		295,643,000	280,463,000
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax		100,000		100,000
Deferred Tax Assets, Tax Credit Carryforwards, Other		162,000		162,000	52,000
Deferred Tax Assets, Net		57,144,000		57,144,000	57,521,000
Federal Statutory Income Tax Rate, Percent	21.00%						35.00%
Increase (Decrease) in Regulatory Liabilities				853,000	7,929,000	0
Effect of TCJA				0	0	(3,376,000)
Regulatory Liability, Noncurrent		625,717,000		625,717,000	611,560,000
Unrecognized Tax Benefits	$ 0	0		0	0	0
Deferred Tax Assets, Goodwill and Intangible Assets		2,723,000		2,723,000	0
Deferred Tax Liabilities, Gross		352,787,000		352,787,000	337,984,000
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income Tax Reconciliation, Income Tax Expense (Benefit), at Federal Statutory Income Tax Rate				16,370,000	19,222,000	39,578,000
Income Tax Reconciliation, State and Local Income Taxes, net of federal tax benefit				4,422,000	4,927,000	5,066,000
Income Tax Reconciliation, Differences Regulatory Commission				(5,772,000)	1,302,000	2,357,000
Effect of TCJA				0	0	(3,376,000)
Income Tax Reconciliation, Other Adjustments				(1,249,000)	(1,184,000)	(2,617,000)
Income Tax Expense (Benefit)				$ 12,642,000	$ 24,191,000	$ 41,008,000
Effective Income Tax Rate				16.20%	26.40%	36.30%
Tax Provision Current And Deferred [Abstract]
Current Federal Tax Expense (Benefit)				$ 5,530,000	$ 8,953,000	$ 19,345,000
Current State and Local Tax Expense (Benefit)				1,667,000	3,785,000	5,963,000
Current Income Tax Expense (Benefit)				7,197,000	12,738,000	25,308,000
Deferred Federal Income Tax Expense (Benefit)				1,515,000	9,001,000	13,869,000
Deferred State and Local Income Tax Expense (Benefit)				3,930,000	2,452,000	1,831,000
Deferred Income Tax Expense (Benefit)				5,445,000	11,453,000	15,700,000
Income Tax Expense (Benefit)				12,642,000	24,191,000	41,008,000
Tax Provision Regulated And Nonutility [Abstract]
Income Tax Expense (Benefit)				12,642,000	24,191,000	41,008,000
Pension Plan [Member]
Regulatory Assets [Line Items]
Deferred Tax Liabilities, Regulatory Assets		22,635,000		22,635,000	27,135,000
Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Deferred Tax Liabilities, Regulatory Assets		19,382,000		19,382,000	21,403,000
Deferred Tax Assets, Regulatory Assets and Liabilities		54,259,000		54,259,000	57,469,000
Northwest Natural Gas Company [Member]
Regulatory Assets [Line Items]
Deferred Tax Rate Differential, Post TCJA				0	(75,000)	0
Regulatory Settlement				(1,129,000)	0	0
Deferred Tax Liabilities, Property, Plant and Equipment		281,044,000		281,044,000	303,186,000
Deferred Tax Liabilities, Leasing Arrangements		40,133,000		40,133,000	0
Deferred Tax Liabilities Non Regulated Liabilities		410,000		410,000	537,000
Deferred Tax Liabilities, Net		309,297,000		309,297,000	294,739,000
Deferred Tax Assets, Tax Credit Carryforwards, Other		48,000		48,000	52,000
Deferred Tax Assets, Net		54,307,000		54,307,000	57,521,000
Increase (Decrease) in Prepaid Taxes		500,000	$ 7,400,000
Increase (Decrease) in Deferred Income Taxes		300,000	4,100,000
Increase (Decrease) in Regulatory Liabilities		200,000	$ 3,300,000	853,000	7,929,000	0
Effect of TCJA				0	0	(2,956,000)
Regulatory Liability, Noncurrent		625,717,000		625,717,000	611,560,000
Deferred Tax Assets, Goodwill and Intangible Assets		0		0	0
Deferred Tax Liabilities, Gross		363,604,000		363,604,000	352,260,000
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income Tax Reconciliation, Income Tax Expense (Benefit), at Federal Statutory Income Tax Rate				17,438,000	19,434,000	39,624,000
Income Tax Reconciliation, State and Local Income Taxes, net of federal tax benefit				4,716,000	4,982,000	5,072,000
Income Tax Reconciliation, Differences Regulatory Commission				(5,772,000)	1,302,000	2,357,000
Effect of TCJA				0	0	(2,956,000)
Income Tax Reconciliation, Other Adjustments				(1,188,000)	(1,184,000)	(2,619,000)
Income Tax Expense (Benefit)				$ 14,065,000	$ 24,459,000	$ 41,478,000
Effective Income Tax Rate				16.90%	26.40%	36.60%
Tax Provision Current And Deferred [Abstract]
Current Federal Tax Expense (Benefit)				$ 6,755,000	$ 9,127,000	$ 19,304,000
Current State and Local Tax Expense (Benefit)				2,101,000	3,846,000	5,956,000
Current Income Tax Expense (Benefit)				8,856,000	12,973,000	25,260,000
Deferred Federal Income Tax Expense (Benefit)				1,340,000	9,025,000	14,371,000
Deferred State and Local Income Tax Expense (Benefit)				3,869,000	2,461,000	1,847,000
Deferred Income Tax Expense (Benefit)				5,209,000	11,486,000	16,218,000
Income Tax Expense (Benefit)				14,065,000	24,459,000	41,478,000
Tax Provision Regulated And Nonutility [Abstract]
Income Tax Expense (Benefit)				14,065,000	24,459,000	$ 41,478,000
Northwest Natural Gas Company [Member] | Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		2,500,000		2,500,000	2,300,000
Northwest Natural Gas Company [Member] | Pension Plan [Member]
Regulatory Assets [Line Items]
Deferred Tax Liabilities, Regulatory Assets		22,635,000		22,635,000	27,135,000
Northwest Natural Gas Company [Member] | Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Deferred Tax Liabilities, Regulatory Assets		19,382,000		19,382,000	21,402,000
Deferred Tax Assets, Regulatory Assets and Liabilities		54,259,000		54,259,000	57,469,000
Regulatory Liabilities		205,000,000		205,000,000	217,100,000
Regulatory Liability, Noncurrent		198,219,000		198,219,000	225,408,000
Northwest Natural Gas Company [Member] | Tax reform deferral [Member]
Regulatory Assets [Line Items]
Regulatory Liability, Noncurrent		8,200,000		8,200,000
Excluding AFUDC [Member] | Northwest Natural Gas Company [Member] | Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		16,900,000		16,900,000	$ 19,100,000
Domestic Tax Authority [Member]
Regulatory Assets [Line Items]
Operating Loss Carryforwards		400,000		400,000
State and Local Jurisdiction [Member]
Regulatory Assets [Line Items]
Operating Loss Carryforwards		$ 400,000		$ 400,000

Property, Plant and Equipment_2

Property, Plant and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	$ 3,476,746	$ 3,414,490
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	1,037,847	993,118
Total property, plant, and equipment, net	2,438,899	2,421,372
Regulatory Liability, Noncurrent	625,717	611,560
Acquired Equipment Capital Leases	0	0
Natural Gas Distribution [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	3,302,049	3,134,122
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	84,965	204,978
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	1,017,931	974,252
Total property, plant, and equipment, net	2,369,083	2,364,848
Northwest Holdings and Northwest Natural [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant, Equipment non-cash	32,502	23,676
Other Northwest Natural [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	63,513	66,009
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	5,548	5,330
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	18,662	18,603
Total property, plant, and equipment, net	50,399	52,736
Northwest Natural Gas Company [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Total property, plant, and equipment, net	2,419,482	2,417,584
Northwest Holdings Other [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	20,671	4,051
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	1,254	263
Total property, plant, and equipment, net	$ 19,417	$ 3,788
Natural Gas Distribution [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	2.90%	2.80%	2.80%
Other Northwest Natural [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Weighted Average Depreciation Rates	1.80%	2.20%	1.90%
Northwest Natural Gas Company [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	$ 3,456,075	$ 3,410,439
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	1,036,593	992,855
Total property, plant, and equipment, net	2,419,482	2,417,584
Regulatory Liability, Noncurrent	625,717	611,560
Northwest Natural Gas Company [Member] | Asset Removal Costs [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Regulatory Liability, Noncurrent	401,893	380,464
North Mist Lease [Member] | Northwest Natural Gas Company [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Transfers and Changes	$ 146,000
New Headquarters Lease [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Lessee, Operating Lease, Lease Not yet Commenced, Term of Contract	20 years
New Headquarters Lease [Member] | Accounting Standards Update 2016-02 [Member] | Build to Suit Lease [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross		$ 26,000

Gas Reserves (Details)

Gas Reserves (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Investments [Line Items]
Gas Reserves, Current	$ 15,278,000	$ 16,647,000
Northwest Natural Gas Company [Member]
Schedule of Investments [Line Items]
Total Cumulative Gas Reserves Investment	188,000,000
Gas Reserves Investment	178,000,000
Cumulative Gross Investment	10,000,000
Additional Rate Per Therm	$ 0.4725
Gas Reserves Percent Gas Supplies YTD	5.00%	6.00%	6.00%
Gas Reserves, Current	$ 15,278,000	$ 16,647,000
Gas Reserves Noncurrent Gross	172,029,000	170,660,000
Gas Reserves Amortization	123,635,000	104,463,000
Total Gas Reserves	63,672,000	82,844,000
Deferred Taxes Related To Gas Reserves	15,515,000	20,071,000
Net Gas Reserves Investment	48,157,000	62,773,000
Investment in Additional Wells, Gas Reserves	$ 3,800,000	$ 4,800,000

Investments (Details)

Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Other Investments [Abstract]
Life Insurance, Corporate or Bank Owned, Amount	$ 49,837	$ 49,922
Equity Method Investments	13,472	13,571
Other Investments	24	65
Total Other investments	$ 63,333	63,558
Trail West Holdings [Member]
Investment [Line Items]
Ownership percentage of TWH	50.00%
Equity Method Investment, Underlying Equity in Net Assets	$ 13,400	13,400
Equity Method Investment Exposure	13,400
Northwest Natural Gas Company [Member]
Other Investments [Abstract]
Life Insurance, Corporate or Bank Owned, Amount	49,837	49,922
Equity Method Investments	0	0
Other Investments	0	0
Total Other investments	$ 49,837	$ 49,922

Business Combinations (Details)

Business Combinations (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)shares
Business Acquisition [Line Items]
Business Combination, Control Obtained Description		Through the purchase of all of the outstanding shares of Falls Water, NWN Water acquired the net assets and 100% control of Falls Water.
Goodwill	$ 49,929	$ 8,954
Sunriver [Member]
Business Acquisition [Line Items]
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual	3,700
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets	221
Consideration transferred	$ 55,000
Connections of acquired business	9,400
Goodwill	$ 40,118
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill	0
Business Acquisition, Goodwill, Expected Tax Deductible Amount	50,200
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	13,819
Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Assets	812
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities	(22)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	54,948
Falls Water Co [Member]
Business Acquisition [Line Items]
Consideration transferred		$ 8,500
Consideration transferred, shares | shares		125,000
Connections of acquired business		5,300 connections
Goodwill		$ 6,200
Other insignificant acquisitions [Member]
Business Acquisition [Line Items]
Consideration transferred	$ 2,000	$ 2,800
Number of Businesses Acquired	3	3

Derivative Instruments - Narrat

Derivative Instruments - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Derivative, Gain on Derivative	$ 17,900,000	$ 7,400,000
Unrealized Gain (Loss) on Derivatives	5,600,000
Derivative, Fair Value, Net	(7,500,000)	5,700,000
Northwest Natural Gas Company [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	9,400,000	3,600,000
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	$ 1,900,000	9,300,000
Northwest Natural Gas Company [Member] | Gas Year 2019 - 2020 [Member] | Financial [Member]
Derivative [Line Items]
TargetHedgeAchieved	52.00%
Northwest Natural Gas Company [Member] | Gas Year 2019 - 2020 [Member] | Physical [Member]
Derivative [Line Items]
TargetHedgeAchieved	19.00%
Northwest Natural Gas Company [Member] | Gas Year 2018 - 2019 [Member] | Financial [Member]
Derivative [Line Items]
TargetHedgeAchieved	48.00%
Northwest Natural Gas Company [Member] | Gas Year 2018 - 2019 [Member] | Physical [Member]
Derivative [Line Items]
TargetHedgeAchieved	24.00%
Collateral Posted with NW Natural Counterparties [Member]
Derivative [Line Items]
Collateral Already Posted, Aggregate Fair Value	$ 0	0
Collateral Posted by NW Natural Counterparties [Member]
Derivative [Line Items]
Collateral Already Posted, Aggregate Fair Value	$ 0	$ 0

Derivative Instruments - Schedu

Derivative Instruments - Schedule of Notional Amounts (Details) - Northwest Natural Gas Company [Member] therm in Thousands, $ in Thousands	Dec. 31, 2019USD ($)therm	Dec. 31, 2018USD ($)therm
Natural Gas Therms [Member] | Financial [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	651,540	408,850
Natural Gas Therms [Member] | Physical [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	512,849	472,275
Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative, Notional Amount | $	$ 6,650	$ 6,936

Derivative Instruments - Sche_2

Derivative Instruments - Schedule of Unrealized and Realized Gain/Loss (Details) - Northwest Holdings and Northwest Natural [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Foreign Exchange Contract [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	$ 0	$ 0
Foreign Exchange Contract [Member] | Cost of Sales [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	102	(284)
Foreign Exchange Contract [Member] | Sales [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	0	0
Natural Gas Commodity [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	(81)	210
Natural Gas Commodity [Member] | Cost of Sales [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	9,863	1,239
Natural Gas Commodity [Member] | Sales [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	(568)	1,660
Deferred Derivative Gain (Loss) [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	(102)	284
Deferred Derivative Gain (Loss) [Member] | Natural Gas Commodity [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	$ (9,376)	$ (211)

- Schedule of Credit Rating Dow

- Schedule of Credit Rating Downgrade Scenarios (Details) - Northwest Natural Gas Company [Member] $ in Thousands	Dec. 31, 2019USD ($)
Moody's, A3 Rating [Member]
Description Of Credit Risk Related Contingent Features [Line Items]
With Adequate Assurance Calls	$ 0
Without Adequate Assurance Calls	0
Moody's, Baa1 Rating [Member]
Description Of Credit Risk Related Contingent Features [Line Items]
With Adequate Assurance Calls	0
Without Adequate Assurance Calls	0
Moody's, Baa2 Rating [Member]
Description Of Credit Risk Related Contingent Features [Line Items]
With Adequate Assurance Calls	0
Without Adequate Assurance Calls	0
Moody's, Baa3 Rating [Member]
Description Of Credit Risk Related Contingent Features [Line Items]
With Adequate Assurance Calls	0
Without Adequate Assurance Calls	0
Speculative [Member]
Description Of Credit Risk Related Contingent Features [Line Items]
With Adequate Assurance Calls	(66)
Without Adequate Assurance Calls	$ (66)

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Leases [Abstract]
Property, Plant and Equipment, Gross	$ 3,476,746	$ 3,414,490
Other Liabilities, Noncurrent	123,388	147,763
Northwest Natural Gas Company [Member]
Leases [Abstract]
Unrecorded Unconditional Purchase Obligation, Purchases	82,200	82,600	$ 85,300
Unrecorded Unconditional Purchase Obligation Offsetting Sales	4,300	4,300	$ 4,500
Property, Plant and Equipment, Gross	3,456,075	3,410,439
Other Liabilities, Noncurrent	$ 123,260	$ 147,668

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Gas Purchase and Pipeline Capacity Purchase and Release Commitments (Details) - Northwest Natural Gas Company [Member] $ in Thousands	Dec. 31, 2019USD ($)
Gas Purchase Agreements [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
2018	$ 86,175
2019	2,899
2020	0
2021	0
2022	0
Thereafter	0
Total	89,074
Less: Amount representing interest	481
Total at present value	88,593
Pipeline Capacity Purchase Agreements [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
2018	76,897
2019	70,638
2020	68,943
2021	68,563
2022	67,052
Thereafter	527,148
Total	879,241
Less: Amount representing interest	147,613
Total at present value	731,628
Pipeline Capacity Release Agreements [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
2018	4,201
2019	3,904
2020	3,904
2021	3,904
2022	3,904
Thereafter	3,253
Total	23,070
Less: Amount representing interest	840
Total at present value	$ 22,230

Environmental Matters (Details)

Environmental Matters (Details)	3 Months Ended		9 Months Ended	12 Months Ended
	Dec. 31, 2019USD ($)	Jun. 30, 2019USD ($)	Sep. 30, 2019USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Accrual for Environmental Loss Contingencies [Abstract]
Site Contingency, Number of Remediation Projects	2			2
Environmental Regulatory Table [Abstract]
Regulatory Assets, Current	$ 41,929,000			$ 41,929,000	$ 41,930,000
Regulatory Assets, Noncurrent	343,146,000			$ 343,146,000	371,786,000
Prudent Costs Deferred During Period	$ 3,000,000		$ 1,500,000
Insurance Proceeds, Amortization Period				10 years 6 months
Cost Recovery Period				3 years
WASHINGTON
Accrual for Environmental Loss Contingencies [Abstract]
Remediation Recovery Percentage	3.32%			3.32%
Northwest Natural Gas Company [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Current Liabilities	$ 39,225,000			$ 39,225,000	33,112,000
Environmental Noncurrent Liabilities	$ 96,797,000			$ 96,797,000	95,636,000
Remediation Recovery Percentage	96.68%			96.68%
EPA Record Of Decision, Clean-Up Costs, Portland Harbor	$ 1,050,000,000			$ 1,050,000,000
Annual Tariff Rider Collection				5,000,000
Environmental Settlement Insurance Proceeds Received To Date	150,000,000			150,000,000
Annual insurance proceeds to appy against remediation costs				5,000,000
Insurance Proceeds Applied To Prudently Incurred Remediation Costs	78,200,000			78,200,000
Environmental Regulatory Table [Abstract]
Regulatory Assets, Current	41,929,000			41,929,000	41,930,000
Regulatory Assets, Noncurrent	343,146,000			343,146,000	371,786,000
Annual Insurance Proceeds to Apply Against Remediation Costs				5,000,000
Total Annual Remediation Expense and Interest				10,000,000
Northwest Natural Gas Company [Member] | Minimum [Member]
Accrual for Environmental Loss Contingencies [Abstract]
EPA Record Of Decision, Clean-Up Costs, Portland Harbor	(0.30)			(0.30)
Northwest Natural Gas Company [Member] | Maximum [Member]
Accrual for Environmental Loss Contingencies [Abstract]
EPA Record Of Decision, Clean-Up Costs, Portland Harbor	0.50			0.50
Northwest Natural Gas Company [Member] | Environmental Restoration Costs [Member]
Environmental Regulatory Table [Abstract]
Environmental Regulatory Deferred Cost and Interest	36,673,000			36,673,000	41,883,000
Environmental Regulatory Accrued Site Liabilities	135,662,000			135,662,000	128,369,000
Environmental Regulatory Insurance Proceeds and Interest	(79,949,000)			(79,949,000)	(88,502,000)
Regulatory Assets	92,386,000			92,386,000	81,750,000
Regulatory Assets, Current	4,762,000			4,762,000	5,601,000
Regulatory Assets, Noncurrent	87,624,000			$ 87,624,000	76,149,000
Portland Harbor [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Number Of Potentially Responsible Parties				one hundred
Gasco Siltronic Sediments [Member] | Minimum [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Exit Costs, Anticipated Cost				$ 57,700,000
Gasco Siltronic Sediments [Member] | Maximum [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Exit Costs, Anticipated Cost				350,000,000
Gasco Siltronic Sediments [Member] | Northwest Natural Gas Company [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Current Liabilities	11,632,000			11,632,000	5,117,000
Environmental Noncurrent Liabilities	46,082,000			46,082,000	44,351,000
Environmental Project Liability	57,700,000			57,700,000
Portland Harbor Other [Member] | Northwest Natural Gas Company [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Current Liabilities	2,543,000			2,543,000	2,600,000
Environmental Noncurrent Liabilities	6,920,000			6,920,000	6,273,000
Gasco Upland [Member] | Northwest Natural Gas Company [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Current Liabilities	14,203,000			14,203,000	13,983,000
Environmental Noncurrent Liabilities	43,616,000			43,616,000	44,830,000
Central Service Center [Member] | Northwest Natural Gas Company [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Current Liabilities	0			0	10,000
Environmental Noncurrent Liabilities	0			0	0
Front Street [Member] | Northwest Natural Gas Company [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Current Liabilities	10,847,000			10,847,000	11,402,000
Environmental Noncurrent Liabilities	0			0	3,000
Undiscounted Environmental Remediation Expense		$ 10,500,000
Liability For Studies And Design Costs	300,000			300,000
Front Street [Member] | Northwest Natural Gas Company [Member] | Environmental Restoration Costs [Member]
Environmental Regulatory Table [Abstract]
Environmental Regulatory Accrued Site Liabilities	400,000			400,000	400,000
Oregon Steel Mills [Member] | Northwest Natural Gas Company [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Current Liabilities	0			0	0
Environmental Noncurrent Liabilities	$ 179,000			$ 179,000	$ 179,000
Yakama Nation [Member] | Portland Harbor Other [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Trustee Council Members - Number of Claimants				1
Site Contingency, Number of Other Third-Party Defendants	29			29
NRD Liability Claim Yakama Nation	$ 300,000			$ 300,000
Number of Amended Complaints Filed				2

Discontinued Operations (Detail

Discontinued Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2017	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 21, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Federal Statutory Income Tax Rate, Percent	21.00%													35.00%
Disposal Group, Including Discontinued Operation, Classified Balance Sheet Disclosures [Abstract]
Discontinued operations - total assets	$ 13,900					$ 13,300						$ 13,300	$ 13,900
Discontinued Operation, Income Statement Disclosures [Abstract]
Loss from discontinued operations, net of tax		$ (1,608)	$ (795)	$ (956)	$ (217)	$ (959)	$ (650)	$ (659)	$ (474)		$ (3,576)	$ (2,742)	$ (127,696)
Loss from discontinued operations per share of common stock
Basic (in dollars per share)		$ (0.05)	$ (0.02)	$ (0.03)	$ (0.01)	$ (0.03)	$ (0.02)	$ (0.02)	$ (0.02)		$ (0.12)	$ (0.10)	$ (4.45)
Diluted (in dollars per share)		$ (0.05)	$ (0.02)	$ (0.03)	$ (0.01)	$ (0.03)	$ (0.02)	$ (0.02)	$ (0.02)		$ (0.12)	$ (0.09)	$ (4.44)
Gill Ranch [Member] | Discontinued Operations, Held-for-sale or Disposed of by Sale [Member]
Disposal Group, Including Discontinued Operation, Classified Balance Sheet Disclosures [Abstract]
Accounts receivable		$ 333				$ 390					$ 333	$ 390
Inventories		695				685					695	685
Other current assets		457				333					457	333
Property, plant, and equipment		13,291				11,621					13,291	11,621
Less: Accumulated depreciation		7				7					7	7
Disposal Group Including Discontinued Operation Operating Lease Right-of-use Asset		118				0					118	0
Other non-current assets		247				247					247	247
Discontinued operations - total assets		15,134				13,269					15,134	13,269
Accounts payable		1,250				873					1,250	873
Other current liabilities		848				307					848	307
Disposal Group, Including Discontinued Operation, Lease Liability, Current		116				0					116	0
Other non-current liabilities		11,495				11,779					11,495	11,779
Total discontinued operations liabilities - current liabilities(1)		$ 13,709				$ 12,959					13,709	12,959
Gill Ranch [Member] | Discontinued Operations, Held-for-sale [Member]
Discontinued Operation, Income Statement Disclosures [Abstract]
Revenues											5,301	3,579	$ 7,135
Operations and maintenance											8,587	5,771	7,245
General taxes											219	479	1,373
Depreciation and amortization											423	430	4,525
Other expenses and interest											931	609	975
Impairment expense											0	0	192,478
Total expenses											10,160	7,289	206,596
Loss from discontinued operations before income tax											(4,859)	(3,710)	(199,461)
Income tax benefit											(1,283)	(968)	(71,765)
Loss from discontinued operations, net of tax											$ (3,576)	$ (2,742)	$ (127,696)
Loss from discontinued operations per share of common stock
Basic (in dollars per share)											$ (0.12)	$ (0.10)	$ (4.45)
Diluted (in dollars per share)											$ (0.12)	$ (0.09)	$ (4.44)
Transferred Subsidiaries - NW Natural Discontinued Operations [Member] | Discontinued Operations, Disposed of by Means Other than Sale [Member]
Discontinued Operation, Income Statement Disclosures [Abstract]
Revenues												$ 3,016	$ 7,360
Operations and maintenance												4,151	7,423
General taxes												448	1,410
Depreciation and amortization												420	4,555
Other expenses and interest												342	650
Impairment expense												0	192,478
Total expenses												5,361	206,516
Loss from discontinued operations before income tax												(2,345)	(199,156)
Income tax benefit												(622)	(71,813)
Loss from discontinued operations, net of tax												(1,723)	$ (127,343)
Gill Ranch [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percent ownership		75.00%									75.00%
Pacific Gas and Electric Company [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percent ownership		25.00%									25.00%
Forecast [Member] | Minimum [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from divestiture of businesses										$ 25,000
Forecast [Member] | Maximum [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from divestiture of businesses										$ 26,500
TCJA Revaluation [Member] | Gill Ranch [Member] | Discontinued Operations, Held-for-sale [Member]
Discontinued Operation, Income Statement Disclosures [Abstract]
Income tax benefit												18,000
TCJA Revaluation [Member] | Transferred Subsidiaries - NW Natural Discontinued Operations [Member] | Discontinued Operations, Held-for-sale [Member]
Discontinued Operation, Income Statement Disclosures [Abstract]
Income tax benefit												$ 18,000

Subsequent Event (Details)

Subsequent Event (Details) - USD ($) $ in Thousands	Jan. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Subsequent Event [Line Items]
Letters of Credit Outstanding, Amount		$ 1,000	$ 2,800
Suncadia [Member]
Subsequent Event [Line Items]
Letters of Credit Outstanding, Amount		$ 1,000
Suncadia [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Business Combination, Consideration Transferred	$ 18,900
Business Acquisition, Connections of Acquired Business	2,800

Quarterly Financial Informati_3

Quarterly Financial Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Entity Information [Line Items]
Operating revenues	$ 247,274	$ 90,317	$ 123,433	$ 285,348	$ 226,702	$ 91,239	$ 124,567	$ 263,635	$ 746,372	$ 706,143	$ 755,038
Net income from continuing operations	38,348	(18,506)	2,051	43,418	36,783	(11,144)	(339)	42,011	65,311	67,311	72,073
Loss from discontinued operations, net of tax	(1,608)	(795)	(956)	(217)	(959)	(650)	(659)	(474)	(3,576)	(2,742)	(127,696)
Net income (loss)	$ 36,740	$ (19,301)	$ 1,095	$ 43,201	$ 35,824	$ (11,794)	$ (998)	$ 41,537	$ 61,735	$ 64,569	$ (55,623)
Average common shares outstanding:
Average common shares outstanding - basic (in shares)	30,448	30,429	29,337	28,906	28,851	28,815	28,791	28,753	29,786	28,803	28,669
Diluted (in shares)	30,521	30,429	29,394	28,970	28,940	28,815	28,791	28,803	29,859	28,873	28,753
Earnings from continuing operations per share of common stock:
Basic (in dollars per share)	$ 1.26	$ (0.61)	$ 0.07	$ 1.50	$ 1.27	$ (0.39)	$ (0.01)	$ 1.46	$ 2.19	$ 2.34	$ 2.51
Diluted (in dollars per share)	1.26	(0.61)	0.07	1.50	1.27	(0.39)	(0.01)	1.46	2.19	2.33	2.51
Loss from discontinued operations per share of common stock:
Basic (in dollars per share)	(0.05)	(0.02)	(0.03)	(0.01)	(0.03)	(0.02)	(0.02)	(0.02)	(0.12)	(0.10)	(4.45)
Diluted (in dollars per share)	(0.05)	(0.02)	(0.03)	(0.01)	(0.03)	(0.02)	(0.02)	(0.02)	(0.12)	(0.09)	(4.44)
Earnings (loss) per share of common stock:
Basic (in dollars per share)	1.21	(0.63)	0.04	1.49	1.24	(0.41)	(0.03)	1.44	2.07	2.24	(1.94)
Diluted (in dollars per share)	$ 1.20	$ (0.63)	$ 0.04	$ 1.49	$ 1.24	$ (0.41)	$ (0.03)	$ 1.44	$ 2.07	$ 2.24	$ (1.93)
Northwest Natural Gas Company [Member]
Entity Information [Line Items]
Operating revenues	$ 245,264	$ 87,592	$ 122,242	$ 284,846	$ 226,146	$ 91,227	$ 124,563	$ 263,635	$ 739,944	$ 705,571	$ 755,038
Net income from continuing operations					37,581	(11,275)	(271)	42,014	68,974	68,049	71,720
Loss from discontinued operations, net of tax					0	(519)	(727)	(477)	0	(1,723)	(127,343)
Net income (loss)	$ 39,613	$ (17,588)	$ 3,054	$ 43,895	$ 37,581	$ (11,794)	$ (998)	$ 41,537	$ 68,974	$ 66,326	$ (55,623)

Condensed Financials Standalo_6

Condensed Financials Standalone Holdco Condensed Financials Standalone Holdco (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Operations and maintenance									$ 178,191	$ 156,698	$ 152,358
Total operating expenses									602,898	573,981	604,136
Income from operations									143,474	132,162	150,902
Other income (expense), net									(22,836)	(3,601)	(295)
Interest expense, net									42,685	37,059	37,526
Income before income taxes									77,953	91,502	113,081
Income Tax Expense (Benefit)									12,642	24,191	41,008
Balance Sheet Related Disclosures [Abstract]
Cash and cash equivalents	$ 9,648			$ 12,633	$ 12,633			$ 3,472	12,633	12,633	3,521	$ 9,648	$ 12,633
Income taxes receivable												256	6,000
Other current assets												38,004	28,472
Total current assets												293,692	295,921
Other investments												63,333	63,558
Other non-current assets												38,464	14,149
Total non-current assets												3,134,762	2,946,741
Total assets												3,428,454	3,242,662
Accounts payable												113,370	115,878
Interest accrued												7,451	7,306
Total current liabilities												482,173	509,084
Long-term debt												(805,955)	(706,247)
Deferred tax liabilities												295,643	280,463
Total deferred credits and other non-current liabilities												1,274,327	1,264,697
Common stock - no par value												558,282	457,640
Retained earnings												318,450	312,182
Total equity												865,999	762,634
Total liabilities and equity												3,428,454	3,242,662
Statement of Cash Flows [Abstract]
Net income (loss)	36,740	$ (19,301)	$ 1,095	43,201	35,824	$ (11,794)	$ (998)	41,537	61,735	64,569	(55,623)
Deferred income taxes									5,445	11,453	15,700
Other									13,907	1,596	2,102
Receivables, net									5,844	181	3,282
Income and other taxes									4,528	(16,904)	6,734
Accounts payable									(16,485)	16,792	1,092
Interest accrued									145	526	807
Other, net									(4,285)	(3,945)	(8,529)
Cash provided by operating activities									185,298	168,771	206,704
Cash used in investing activities									(303,781)	(217,453)	(214,172)
Cash dividend payments on common stock									(53,339)	(51,311)	(53,957)
Other									(2,614)	(715)	(2,309)
Cash provided by financing activities									115,498	57,843	7,419
Increase (decrease) in cash and cash equivalents									(2,985)	9,161	(49)
Cash and cash equivalents, beginning of period				12,633				3,472	12,633	3,472	3,521
Cash and cash equivalents, end of period	9,648				12,633				9,648	12,633	3,472
Short-term Debt												149,100	217,620
Accrued Income Taxes, Current												11,971	11,023
Other Liabilities, Current												62,705	54,492
Deferred Income Taxes and Tax Credits									(6,317)	(14,356)	52,414
Proceeds from Stock Options Exercised									2,015	1,546	4,819
Proceeds from Issuance of Common Stock									92,956	0	0
Proceeds from (Repayments of) Short-term Debt									(68,520)	163,274	900
Parent Company, Condensed Statement of Cash Flows [Member]
Income Statement [Abstract]
Equity in earnings of subsidiaries, net of tax					(36,469)				(64,328)
Balance Sheet Related Disclosures [Abstract]
Cash and cash equivalents	119			4,011	4,011			0	4,011	4,011	0	119	4,011
Statement of Cash Flows [Abstract]
Net income (loss)					(35,839)				(61,735)
Equity in earnings of subsidiaries, net of tax					(36,469)				(64,328)
Other					15				66
Receivables, net					(585)				846
Income and other taxes					(9,034)				4,325
Accounts payable					9,304				(5,177)
Interest accrued					32				(32)
Other, net					(44)				(346)
Cash provided by operating activities					(935)				(3,109)
Contributions to subsidiaries					(1,804)				(157,591)
Cash used in investing activities					(1,804)				(157,591)
Cash dividend payments on common stock					(12,923)				(53,339)
Capital contributions					(20,000)				0
Other					(327)				2,737
Cash provided by financing activities					6,750				156,808
Increase (decrease) in cash and cash equivalents					4,011				(3,892)
Cash and cash equivalents, beginning of period				4,011				0	4,011	0
Cash and cash equivalents, end of period	119				4,011				119	4,011	0
Deferred Income Taxes and Tax Credits					(7)				198
Proceeds from Stock Options Exercised					0				2,015
Proceeds from Issuance of Common Stock					0				92,956
Proceeds from (Repayments of) Short-term Debt					0				24,000
SEC Schedule, 12-04, Cash Dividends Paid to Registrant, Consolidated Subsidiaries					0				88,439
Parent Company, Condensed Balance Sheet [Member]
Balance Sheet Related Disclosures [Abstract]
Cash and cash equivalents	119			4,011	4,011				4,011	4,011		119	4,011
Receivables from affiliates												1,950	2,796
Income taxes receivable												256	6,000
Other current assets												4,600	3,078
Total current assets												6,925	15,885
Investments in subsidiaries												888,477	754,971
Other investments												24	65
Other non-current assets												245	310
Total non-current assets												888,937	755,346
Total assets												895,862	771,231
Accounts payable												612	168
Payables to affiliates												3,697	9,166
Interest accrued												0	32
Total current liabilities												28,473	9,366
Long-term debt												0	(1)
Deferred tax liabilities												0	7
Total deferred credits and other non-current liabilities												0	7
Common stock - no par value												840,364	739,722
Retained earnings												27,025	22,137
Total equity												867,389	761,859
Total liabilities and equity												895,862	771,231
Statement of Cash Flows [Abstract]
Cash and cash equivalents, beginning of period				4,011					4,011
Cash and cash equivalents, end of period	119				4,011				119	4,011
Deferred Income Tax Assets, Net												191	0
Short-term Debt												24,000	0
Accrued Income Taxes, Current												127	0
Other Liabilities, Current												37	0
Parent Company, Condensed Income Statement [Member]
Income Statement [Abstract]
Operations and maintenance					838				2,747
Total operating expenses					838				2,747
Income from operations					(838)				(2,747)
Equity in earnings of subsidiaries, net of tax					(36,469)				(64,328)
Other income (expense), net					36				(22)
Interest expense, net					53				726
Income before income taxes					35,614				60,833
Income Tax Expense (Benefit)					(225)				(902)
Statement of Cash Flows [Abstract]
Net income (loss)					35,839				61,735
Equity in earnings of subsidiaries, net of tax					(36,469)				(64,328)
Northwest Natural Gas Company [Member]
Income Statement [Abstract]
Total operating expenses									592,598	572,472	604,116
Income from operations									147,346	133,099	150,922
Other income (expense), net									(22,968)	(3,599)	(198)
Interest expense, net									41,339	36,992	37,526
Income before income taxes									83,039	92,508	113,198
Income Tax Expense (Benefit)									14,065	24,459	41,478
Balance Sheet Related Disclosures [Abstract]
Cash and cash equivalents	5,919			7,947	7,947			3,110	7,947	3,110	3,380	5,919	7,947
Receivables from affiliates												787	4,166
Other current assets												33,258	25,347
Total current assets												270,159	272,786
Other investments												49,837	49,922
Other non-current assets												38,062	13,736
Total non-current assets												3,051,328	2,919,950
Total assets												3,321,487	3,192,736
Accounts payable												111,641	114,937
Payables to affiliates												1,546	523
Interest accrued												7,441	7,273
Total current liabilities												442,426	494,056
Long-term debt												(769,081)	(704,134)
Deferred tax liabilities												309,297	294,739
Total deferred credits and other non-current liabilities												1,287,784	1,278,878
Common stock - no par value												319,557	226,452
Retained earnings												513,372	496,404
Total equity												822,196	715,668
Total liabilities and equity												3,321,487	3,192,736
Statement of Cash Flows [Abstract]
Net income (loss)	39,613	$ (17,588)	$ 3,054	43,895	37,581	$ (11,794)	$ (998)	41,537	68,974	66,326	(55,623)
Deferred income taxes									5,209	11,486	16,218
Other									12,317	883	2,003
Receivables, net									9,264	(3,920)	3,215
Income and other taxes									496	(7,854)	6,730
Accounts payable									(18,548)	13,937	3,332
Interest accrued									168	500	807
Other, net									(2,309)	(3,958)	(8,291)
Cash provided by operating activities									186,176	173,508	206,483
Cash used in investing activities									(243,077)	(238,462)	(214,172)
Cash dividend payments on common stock									(53,372)	(38,387)	(53,957)
Capital contributions									(93,155)	0	0
Other									(2,510)	(1,539)	(2,309)
Cash provided by financing activities									54,873	69,791	7,419
Increase (decrease) in cash and cash equivalents									(2,028)	4,837	(270)
Cash and cash equivalents, beginning of period				$ 7,947				$ 3,110	7,947	3,110	3,380
Cash and cash equivalents, end of period	$ 5,919				7,947				5,919	7,947	3,110
Short-term Debt												125,100	217,500
Accrued Income Taxes, Current												11,717	10,990
Other Liabilities, Current												$ 61,438	$ 53,027
Deferred Income Taxes and Tax Credits									(4,046)	(12,330)	(15,894)
Proceeds from Stock Options Exercised									0	1,368	4,819
Proceeds from (Repayments of) Short-term Debt									(92,400)	$ 163,300	$ 900
Northwest Natural Gas Company [Member] | Parent Company, Condensed Income Statement [Member]
Income Statement [Abstract]
Equity in earnings of subsidiaries, net of tax					(35,600)				(64,300)
Statement of Cash Flows [Abstract]
Equity in earnings of subsidiaries, net of tax					$ (35,600)				$ (64,300)

Valuation Allowances and Rese_3

Valuation Allowances and Reserves (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Entity Information [Line Items]
Allowance for Doubtful Accounts Receivable, beginning of period	$ 977	$ 956	$ 1,290
Valuation Allowances and Reserves, Charged to Cost and Expense	450	680	865
Valuation Allowances and Reserves, Charged to Other Accounts	0	0	0
SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction	754	659	1,199
Allowance for Doubtful Accounts Receivable, end of period	673	977	956
Northwest Natural Gas Company [Member]
Entity Information [Line Items]
Allowance for Doubtful Accounts Receivable, beginning of period	975	956	1,290
Valuation Allowances and Reserves, Charged to Cost and Expense	450	678	865
Valuation Allowances and Reserves, Charged to Other Accounts	0	0	0
SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction	753	659	1,199
Allowance for Doubtful Accounts Receivable, end of period	$ 672	$ 975	$ 956