Otter Tail (OTTR) 10-Q 3 Nov 21 2021 Q3 Quarterly report Financial data

Cover

Cover - shares	9 Months Ended
	Sep. 30, 2021	Oct. 29, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
Document Transition Report	false
Entity File Number	0-53713
Entity Registrant Name	OTTER TAIL CORPORATION
Entity Incorporation, State or Country Code	MN
Entity Tax Identification Number	27-0383995
Entity Address, Address Line One	215 South Cascade Street
Entity Address, Address Line Two	Box 496
Entity Address, City or Town	Fergus Falls
Entity Address, State or Province	MN
Entity Address, Postal Zip Code	56538-0496
City Area Code	866
Local Phone Number	410-8780
Title of 12(b) Security	Common Shares, par value $5.00 per share
Trading Symbol	OTTR
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		41,539,984
Entity Central Index Key	0001466593
Amendment Flag	false
Document Fiscal Period Focus	Q3
Document Fiscal Year Focus	2021
Current Fiscal Year End Date	--12-31

Consolidated Balance Sheets (un

Consolidated Balance Sheets (unaudited) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current Assets
Cash and Cash Equivalents	$ 1,272	$ 1,163
Receivables, net of allowance for credit losses	178,759	113,959
Inventories	114,615	92,165
Regulatory Assets	22,517	21,900
Other Current Assets	17,804	5,645
Total Current Assets	334,967	234,832
Noncurrent Assets
Investments	55,456	51,856
Property, Plant and Equipment, net of accumulated depreciation	2,083,223	2,049,273
Regulatory Assets	158,515	168,395
Intangible Assets, net of accumulated amortization	9,319	10,144
Goodwill	37,572	37,572
Other Noncurrent Assets	34,096	26,282
Total Noncurrent Assets	2,378,181	2,343,522
Total Assets	2,713,148	2,578,354
Current Liabilities
Short-Term Debt	97,857	80,997
Current Maturities of Long-Term Debt	169,962	140,087
Accounts Payable	135,437	130,805
Accrued Salaries and Wages	28,455	26,908
Accrued Taxes	17,972	18,831
Regulatory Liabilities	25,323	16,663
Other Current Liabilities	35,081	22,495
Total Current Liabilities	510,087	436,786
Noncurrent Liabilities and Deferred Credits
Pensions Benefit Liability	101,446	114,055
Other Postretirement Benefits Liability	68,090	67,359
Regulatory Liabilities	230,733	233,973
Deferred Income Taxes	176,502	153,376
Deferred Tax Credits	16,847	17,405
Other Noncurrent Liabilities	62,342	60,002
Total Noncurrent Liabilities and Deferred Credits	655,960	646,170
Commitments and Contingencies (Note 9)
Capitalization
Long-Term Debt, net of current maturities	594,619	624,432
Shareholders' Equity
Common Shares: 50,000,000 shares authorized of $5 par value; 41,539,984 and 41,469,879 outstanding at September 30, 2021 and December 31, 2020	207,700	207,349
Additional Paid-In Capital	418,568	414,246
Retained Earnings	334,385	257,878
Accumulated Other Comprehensive Loss	(8,171)	(8,507)
Total Shareholders' Equity	952,482	870,966
Total Capitalization	1,547,101	1,495,398
Total Liabilities and Shareholders' Equity	$ 2,713,148	$ 2,578,354

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parentheticals) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
Shareholders' Equity
Common stock, shares authorized (in shares)	50,000,000	50,000,000
Common stock, par value (in dollars per share)	$ 5	$ 5
Common stock, shares outstanding (in shares)	41,539,984	41,469,879

Consolidated Statements of Inco

Consolidated Statements of Income (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating Revenues
Total Operating Revenues	$ 316,294	$ 235,755	$ 863,612	$ 663,258
Operating Expenses
Electric Production Fuel	17,698	11,554	44,576	34,077
Electric Purchased Power	9,878	13,428	40,273	45,940
Electric Operating and Maintenance Expenses	36,465	32,845	114,615	106,639
Cost of Products Sold (excluding depreciation)	134,212	86,856	358,767	246,567
Other Nonelectric Expenses	16,224	13,615	45,587	36,277
Depreciation and Amortization	22,815	20,395	68,109	61,230
Electric Property Taxes	4,474	4,333	13,136	12,601
Total Operating Expenses	241,766	183,026	685,063	543,331
Operating Income	74,528	52,729	178,549	119,927
Other Income and Expense
Interest Charges	9,648	8,568	28,601	25,353
Nonservice Cost Components of Postretirement Benefits	505	842	1,511	2,581
Other Income (Expense), net	203	1,712	2,095	3,733
Income Before Income Taxes	64,578	45,031	150,532	95,726
Income Tax Expense	11,824	9,097	25,380	18,543
Net Income	$ 52,754	$ 35,934	$ 125,152	$ 77,183
Weighted-Average Common Shares Outstanding:
Basic (in shares)	41,504	40,914	41,487	40,548
Diluted (in shares)	41,869	41,078	41,795	40,733
Earnings Per Share:
Basic (in dollars per share)	$ 1.27	$ 0.88	$ 3.02	$ 1.90
Diluted (in dollars per share)	$ 1.26	$ 0.87	$ 2.99	$ 1.89
Electric
Operating Revenues
Total Operating Revenues	$ 118,775	$ 115,213	$ 348,629	$ 333,213
Product Sales
Operating Revenues
Total Operating Revenues	$ 197,519	$ 120,542	$ 514,983	$ 330,045

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Net Income	$ 52,754	$ 35,934	$ 125,152	$ 77,183
Unrealized Gain (Loss) on Available-for-Sale Securities:
Reversal of Previously Recognized Losses (Gains) Realized on Sale of Investments and Included in Other Income (Expense)	0	(21)	(43)	13
Unrealized Gains (Losses)	(33)	(13)	(85)	205
Income Tax (Expense) Benefit	7	7	27	(46)
Available-for-Sale Securities, net of tax	(26)	(27)	(101)	172
Pension and Postretirement Benefit Plans:
Amortization of Unrecognized Postretirement Benefit Losses and Costs	197	138	591	413
Income Tax Expense	(51)	(36)	(154)	(108)
Pension and Postretirement Benefit Plan, net of tax	146	102	437	305
Total Other Comprehensive Income	120	75	336	477
Total Comprehensive Income	$ 52,874	$ 36,009	$ 125,488	$ 77,660

Consolidated Statements of Shar

Consolidated Statements of Shareholders' Equity (unaudited) - USD ($) $ in Thousands	Total	Common Shares	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)		Unrealized Gain on Available-for-Sale Debt, net of tax	Unamortized Actuarial Losses and Prior Service Costs Related to Pension and Postretirement Benefits, net of tax
Beginning balance, shares (in shares) at Dec. 31, 2019		40,157,591
Beginning balance at Dec. 31, 2019	$ 781,482	$ 200,788	$ 364,790	$ 222,341	$ (6,437)	[1]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock Issuances, Net of Expenses (in shares)		932,791
Common Stock Issuances, Net of Expenses	34,771	$ 4,664	30,107
Common Stock Retirements and Forfeitures (in shares)		(38,217)
Common Stock Retirements and Forfeitures	(2,069)	$ (191)	(1,878)
Net Income	77,183			77,183
Other Comprehensive Income	477				477	[1]
Stock Compensation Expense	5,282		5,282
Common Dividends	(45,056)			(45,056)
Ending balance, shares (in shares) at Sep. 30, 2020		41,052,165
Ending balance at Sep. 30, 2020	852,070	$ 205,261	398,301	254,468	(5,960)	[1]
Beginning balance, shares (in shares) at Jun. 30, 2020		40,848,828
Beginning balance at Jun. 30, 2020	822,055	$ 204,244	390,141	233,705	(6,035)	[1]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock Issuances, Net of Expenses (in shares)		203,337
Common Stock Issuances, Net of Expenses	7,902	$ 1,017	6,885
Net Income	35,934			35,934
Other Comprehensive Income	75				75	[1]
Stock Compensation Expense	1,275		1,275
Common Dividends	(15,171)			(15,171)
Ending balance, shares (in shares) at Sep. 30, 2020		41,052,165
Ending balance at Sep. 30, 2020	852,070	$ 205,261	398,301	254,468	(5,960)	[1]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Before Tax					(11,528)		$ 265	$ (11,793)
Tax Effect					3,021		(56)	3,077
Beginning balance, shares (in shares) at Dec. 31, 2020		41,469,879
Beginning balance at Dec. 31, 2020	870,966	$ 207,349	414,246	257,878	(8,507)	[1]	209	(8,716)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock Issuances, Net of Expenses (in shares)		105,806
Common Stock Issuances, Net of Expenses	(48)	$ 530	(578)
Common Stock Retirements and Forfeitures (in shares)		(35,701)
Common Stock Retirements and Forfeitures	(1,633)	$ (179)	(1,454)
Net Income	125,152			125,152
Other Comprehensive Income	336				336	[1]
Stock Compensation Expense	6,354		6,354
Common Dividends	(48,645)			(48,645)
Ending balance, shares (in shares) at Sep. 30, 2021		41,539,984
Ending balance at Sep. 30, 2021	952,482	$ 207,700	418,568	334,385	(8,171)	[1]	108	(8,279)
Beginning balance, shares (in shares) at Jun. 30, 2021		41,538,709
Beginning balance at Jun. 30, 2021	915,123	$ 207,694	417,870	297,850	(8,291)	[1]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock Issuances, Net of Expenses (in shares)		1,275
Common Stock Issuances, Net of Expenses	0	$ 6	(6)
Common Stock Retirements and Forfeitures (in shares)		0
Common Stock Retirements and Forfeitures	(126)	$ 0	(126)
Net Income	52,754			52,754
Other Comprehensive Income	120				120	[1]
Stock Compensation Expense	830		830
Common Dividends	(16,219)			(16,219)
Ending balance, shares (in shares) at Sep. 30, 2021		41,539,984
Ending balance at Sep. 30, 2021	$ 952,482	$ 207,700	$ 418,568	$ 334,385	(8,171)	[1]	108	(8,279)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Before Tax					(11,065)		137	(11,202)
Tax Effect					$ 2,894		$ (29)	$ 2,923
[1]	1 Accumulated Other Comprehensive Income (Loss) as of September 30, 2021 and December 31, 2020 is comprised of the following: (in thousands) September 30, December 31, Unrealized Gain on Available-for-Sale Debt Securities: Before Tax $ 137 $ 265 Tax Effect (29) (56) Unrealized Gain on Available-for-Sale Debt, net of tax 108 209 Unamortized Actuarial Losses and Prior Service Costs Related to Pension and Postretirement Benefits: Before Tax (11,202) (11,793) Tax Effect 2,923 3,077 Unamortized Actuarial Losses and Prior Service Costs Related to Pension and Postretirement Benefits, net of tax (8,279) (8,716) Accumulated Other Comprehensive Loss: Before Tax (11,065) (11,528) Tax Effect 2,894 3,021 Net Accumulated Other Comprehensive Loss $ (8,171) $ (8,507)

Consolidated Statements of Sh_2

Consolidated Statements of Shareholders' Equity (Parentheticals) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Stockholders' Equity [Abstract]
Common Dividends (in dollars per share)	$ 0.39	$ 0.37	$ 1.17	$ 1.11

Consolidated Statements of Cash

Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Operating Activities
Net Income	$ 125,152	$ 77,183
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:
Depreciation and Amortization	68,109	61,230
Deferred Tax Credits	(558)	(986)
Deferred Income Taxes	18,835	20,353
Change in Deferred Debits and Other Assets	6,166	3,439
Discretionary Contribution to Pension Plan	(10,000)	(11,200)
Change in Noncurrent Liabilities and Deferred Credits	2,662	3,237
Allowance for Equity Funds Used During Construction	(427)	(3,104)
Stock Compensation Expense	6,354	5,282
Other, Net	(3,480)	(176)
Cash (Used for) Provided by Current Assets and Current Liabilities:
Change in Receivables	(64,800)	(20,025)
Change in Inventories	(22,450)	15,980
Change in Other Current Assets	(12,159)	2,023
Change in Payables and Other Current Liabilities	40,574	(12,063)
Change in Interest Payable and Income Taxes Receivable/Payable	774	103
Net Cash Provided by Operating Activities	154,752	141,276
Investing Activities
Capital Expenditures	(117,312)	(220,630)
Proceeds from Disposal of Noncurrent Assets	5,819	4,617
Cash Used for Investments and Other Assets	(5,591)	(6,372)
Net Cash Used in Investing Activities	(117,084)	(222,385)
Financing Activities
Change in Checks Written in Excess of Cash	(3,133)	90
Net Short-Term Borrowings	16,860	42,600
Proceeds from Issuance of Common Stock	0	35,219
Common Stock Issuance Expenses	(67)	(465)
Payments for Shares Withheld for Employee Tax Obligations	(1,633)	(2,069)
Proceeds from Issuance of Long-Term Debt	0	75,000
Debt Issuance Expenses	(772)	(369)
Payments for Retirement of Long-Term Debt	(169)	(136)
Dividends Paid	(48,645)	(45,056)
Net Cash (Used in) Provided by Financing Activities	(37,559)	104,814
Net Change in Cash and Cash Equivalents	109	23,705
Cash and Cash Equivalents at Beginning of Period	1,163	21,199
Cash and Cash Equivalents at End of Period	1,272	44,904
Supplemental Disclosure of Noncash Investing Activities
Accrued Property, Plant, and Equipment Additions	$ 14,358	$ 112,314

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Overview Otter Tail Corporation and its subsidiaries (collectively, the "Company", "us", "our" or "we") form a diverse, multi-platform business consisting of a vertically integrated, regulated utility with generation, transmission and distribution facilities complemented by manufacturing businesses providing metal fabrication for custom machine parts and metal components, manufacturing of extruded and thermoformed plastic products, and manufacturing of PVC pipe products. We classify our business into three segments: Electric, Manufacturing and Plastics. Basis of Presentation The unaudited consolidated financial statements included herein have been prepared pursuant to the rules and regulations of the SEC for interim reporting. Accordingly, they do not include all the information and footnotes required by generally accepted accounting principles. In the opinion of management, we have included all adjustments, including normal recurring accruals, necessary for a fair presentation of the consolidated financial statements for the periods presented. The consolidated financial statements and condensed notes thereto should be read in conjunction with the consolidated financial statements and notes included in our Annual Report on Form 10-K for the fiscal year ended December 31, 2020. Because of the coronavirus (COVID-19) pandemic, the seasonality of our businesses and other factors, the earnings for the three and nine months ended September 30, 2021 should not be taken as an indication of earnings for all or any part of the balance of the current year or as an indication of earnings for future years. Use of Estimates We use estimates based on the best information available in recording transactions and balances resulting from business operations. As better information becomes available, or actual amounts are known, the recorded estimates are revised. Consequently, operating results can be affected by revisions to prior accounting estimates.

Segment Information

Segment Information	9 Months Ended
	Sep. 30, 2021
Segment Reporting [Abstract]
Segment Information	Segment Information We classify our business into three segments, Electric, Manufacturing and Plastics, consistent with our business strategy, organizational structure and our internal reporting and review processes used by our chief operating decision maker to make decisions regarding allocation of resources, to assess operating performance and to make strategic decisions. Certain assets and costs are not allocated to our operating segments. Corporate operating costs include items such as corporate staff and overhead costs, the results of our captive insurance company and other items excluded from the measurement of operating segment performance. Corporate assets consist primarily of cash, prepaid expenses, investments and fixed assets. Corporate is not an operating segment, rather it is added to operating segment totals to reconcile to consolidated amounts. Information for each segment and our unallocated corporate costs for the three and nine months ended September 30, 2021 and 2020 are as follows: Three Months Ended September 30, Nine Months Ended September 30, (in thousands) 2021 2020 2021 2020 Operating Revenue 1 Electric $ 118,775 $ 115,213 $ 348,629 $ 333,213 Manufacturing 89,977 59,849 250,085 174,276 Plastics 107,542 60,693 264,898 155,769 Total $ 316,294 $ 235,755 $ 863,612 $ 663,258 Net Income (Loss) Electric $ 22,528 $ 24,737 $ 55,547 $ 54,225 Manufacturing 4,200 3,311 15,290 8,476 Plastics 28,410 10,343 60,102 20,922 Corporate (2,384) (2,457) (5,787) (6,440) Total $ 52,754 $ 35,934 $ 125,152 $ 77,183 1 Amounts reflect operating revenues to external customers. Intersegment operating revenues are not material for any period presented. The following provides the identifiable assets by segment and corporate assets as of September 30, 2021 and December 31, 2020: (in thousands) September 30, December 31, Identifiable Assets Electric $ 2,271,636 $ 2,233,399 Manufacturing 242,414 191,005 Plastics 143,615 99,767 Corporate 55,483 54,183 Total $ 2,713,148 $ 2,578,354

Revenue

Revenue	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
Revenue	Revenue We present our operating revenues to external customers, in total and by amounts arising from contracts with customers and alternative revenue program (ARP) arrangements, disaggregated by revenue source and segment for the three and nine months ended September 30, 2021 and 2020: Three Months Ended September 30, Nine Months Ended September 30, (in thousands) 2021 2020 2021 2020 Operating Revenues Electric Segment Retail: Residential $ 33,902 $ 32,734 $ 100,067 $ 96,440 Retail: Commercial and Industrial 60,557 64,918 185,376 189,771 Retail: Other 1,979 1,953 5,687 5,550 Total Retail 96,438 99,605 291,130 291,761 Transmission 13,300 12,288 37,085 32,802 Wholesale 6,944 1,500 14,711 3,141 Other 2,093 1,820 5,703 5,509 Total Electric Segment 118,775 115,213 348,629 333,213 Manufacturing Segment Metal Parts and Tooling 76,455 50,957 210,141 145,435 Plastic Products and Tooling 10,198 7,600 30,624 25,323 Scrap Metal Sales 3,324 1,292 9,320 3,518 Total Manufacturing Segment 89,977 59,849 250,085 174,276 Plastics Segment PVC Pipe 107,542 60,693 264,898 155,769 Total Operating Revenue 316,294 235,755 863,612 663,258 Less: Non-contract Revenues Included Above Electric Segment - ARP Revenues (33) 2,778 (2,790) 2,900 Total Operating Revenues from Contracts with Customers $ 316,327 $ 232,977 $ 866,402 $ 660,358

Select Balance Sheet Informatio

Select Balance Sheet Information	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Select Balance Sheet Information	Select Balance Sheet Information Receivables and Allowance for Credit Losses Receivables as of September 30, 2021 and December 31, 2020 are as follows: (in thousands) September 30, December 31, Receivables Trade $ 152,906 $ 87,048 Other 11,182 8,939 Unbilled Receivables 17,003 21,187 Total Receivables 181,091 117,174 Less: Allowance for Credit Losses 2,332 3,215 Receivables, net of allowance for credit losses $ 178,759 $ 113,959 The following is a summary of activity in the allowance for credit losses for the nine months ended September 30, 2021 and 2020: (in thousands) 2021 2020 Beginning Balance, January 1 $ 3,215 $ 1,339 Additions Charged to Expense 177 1,845 Reductions for Amounts Written Off, Net of Recoveries (1,060) (923) Ending Balance, September 30 $ 2,332 $ 2,261 Inventories Inventories consist of the following as of September 30, 2021 and December 31, 2020: (in thousands) September 30, December 31, Finished Goods $ 25,727 $ 22,046 Work in Process 29,932 16,210 Raw Material, Fuel and Supplies 58,956 53,909 Total Inventories $ 114,615 $ 92,165 Investments The following is a summary of our investments as of September 30, 2021 and December 31, 2020: (in thousands) September 30, December 31, Corporate-Owned Life Insurance Policies $ 40,096 $ 36,825 Debt Securities 9,208 9,260 Money Market Funds 953 4,075 Mutual Funds 5,170 1,662 Other Investments 29 34 Total Investments $ 55,456 $ 51,856 The amount of unrealized gains and losses on debt securities as of September 30, 2021 and December 31, 2020 are not material and no unrealized losses were deemed to be other-than-temporary. In addition, the amount of unrealized gains and losses on marketable equity securities still held as of September 30, 2021 and December 31, 2020 are not material. Property, Plant and Equipment Major classes of property, plant and equipment as of September 30, 2021 and December 31, 2020 include: (in thousands) September 30, December 31, Electric Plant in Service Electric Plant in Service $ 2,705,778 $ 2,531,352 Construction Work in Progress 100,495 203,078 Total Gross Electric Plant 2,806,273 2,734,430 Less Accumulated Depreciation and Amortization 822,441 778,988 Net Electric Plant 1,983,832 1,955,442 Nonelectric Property, Plant and Equipment Nonelectric Property, Plant and Equipment in Service 263,880 258,730 Construction Work in Progress 15,564 9,290 Total Gross Nonelectric Property, Plant and Equipment 279,444 268,020 Less Accumulated Depreciation and Amortization 180,053 174,189 Net Nonelectric Property, Plant and Equipment 99,391 93,831 Net Property, Plant and Equipment $ 2,083,223 $ 2,049,273

Regulatory Matters

Regulatory Matters	9 Months Ended
	Sep. 30, 2021
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Matters	Regulatory Matters Regulatory Assets and Liabilities The following presents our current and long-term regulatory assets and liabilities as of September 30, 2021 and December 31, 2020 and the period we expect to recover or refund such amounts: Period of September 30, 2021 December 31, 2020 (in thousands) Recovery/Refund Current Long-Term Current Long Term Regulatory Assets Pension and Other Postretirement Benefit Plans 1 Various $ 11,037 $ 139,467 $ 11,037 $ 146,071 Alternative Revenue Program Riders 2 Up to 3 years 7,229 8,225 8,871 9,373 Asset Retirement Obligations 1 Asset lives — 7,065 — 8,462 ISO Cost Recovery Trackers 1 Up to 2 years 270 1,027 1,079 867 Unrecovered Project Costs 1 Up to 3 years 3,227 1,456 361 2,989 Deferred Rate Case Expenses 1 Various 637 936 360 230 Debt Reacquisition Premiums 1 Up to 12 years 117 262 192 341 Other 1 Various — 77 — 62 Total Regulatory Assets $ 22,517 $ 158,515 $ 21,900 $ 168,395 Regulatory Liabilities Deferred Income Taxes Asset lives $ — $ 130,555 $ — $ 134,719 Plant Removal Obligations Asset lives 5,893 96,734 — 98,707 Fuel Clause Adjustments Up to 1 year 5,692 — 10,947 — Alternative Revenue Program Riders Various 5,265 2,507 3,581 470 Pension and Other Postretirement Benefit Plans Up to 1 year 1,959 — 1,959 — Derivative Instruments Various 6,136 787 — — Other Various 378 150 176 77 Total Regulatory Liabilities $ 25,323 $ 230,733 $ 16,663 $ 233,973 1 Costs subject to recovery without a rate of return. 2 Amount eligible for recovery includes an incentive or rate of return.

Short-Term and Long-Term Borrow

Short-Term and Long-Term Borrowings	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Short-Term and Long-Term Borrowings	Short-Term and Long-Term Borrowings The following is a summary of our outstanding short and long-term borrowings by borrower, Otter Tail Corporation (OTC) or Otter Tail Power Company (OTP), as of September 30, 2021 and December 31, 2020: Short-Term Debt The following is a summary of our lines of credit as of September 30, 2021 and December 31, 2020: September 30, 2021 December 31, (in thousands) Line Limit Amount Outstanding Letters Amount Available Amount Available OTC Credit Agreement $ 170,000 $ 36,624 $ — $ 133,376 $ 104,834 OTP Credit Agreement 170,000 61,233 13,159 95,608 140,068 Total $ 340,000 $ 97,857 $ 13,159 $ 228,984 $ 244,902 On September 30, 2021, OTC entered into a Fourth Amended and Restated Credit Agreement (the OTC Credit Agreement) and OTP entered into a Third Amended and Restated Credit Agreement (the OTP Credit Agreement) amending and restating the previously existing credit agreements to extend the maturity date of each agreement to September 30, 2026. The agreements both provide for $170 million revolving lines of credit to support operations, and borrowings which may be used for working capital needs and other capital requirements, to refinance certain indebtedness and for the issuance of letters of credit in an aggregate not to exceed $40 million for the OTC Credit Agreement and $50 million for the OTP Credit Agreement. Each credit facility includes an accordion provision allowing the borrower to increase the available borrowing capacity, subject to certain terms and conditions. The borrowing capacity of the OTC Credit Agreement can be increased to $290 million and the OTP Credit Agreement can be increased to $250 million. Borrowings under each credit facility are subject to a variable rate of interest on outstanding balances and a commitment fee is applied based on the average unused amount available to be drawn under the respective facility. The variable rate of interest to be charged is based on either LIBOR or a Base Rate, as defined in the agreement, selected by the borrower at the time of an advance, subject to the conditions of each agreement, plus an applicable credit spread. The credit spread ranges from 0.125% to 2.00% for the OTC Credit Agreement and from zero to 1.75% for the OTP Credit Agreement, depending on the benchmark interest rate selected and is subject to adjustment based on the credit ratings of the borrower. As of September 30, 2021, the weighted-average LIBOR Rate based interest rate was 1.59% and 1.33% under the OTC Credit Agreement and OTP Credit Agreement, respectively. Each credit facility contains a number of restrictions on the borrower, including restrictions on their ability to merge, sell assets, make investments, create or incur liens on assets, guarantee the obligations of any other party and engage in transactions with related parties. The agreements also contain certain financial and non-financial covenants and defined events of default, and include provisions for the replacement of the LIBOR benchmark rate in the event that LIBOR is no longer available. Long-Term Debt The following is a summary of outstanding long-term debt by borrower as of September 30, 2021 and December 31, 2020: (in thousands) Entity Debt Instrument Rate Maturity September 30, December 31, OTC Guaranteed Senior Notes 3.55% 12/15/26 $ 80,000 $ 80,000 OTP Series 2011A Senior Unsecured Notes 4.63% 12/01/21 140,000 140,000 OTP Series 2007B Senior Unsecured Notes 6.15% 08/20/22 30,000 30,000 OTP Series 2007C Senior Unsecured Notes 6.37% 08/02/27 42,000 42,000 OTP Series 2013A Senior Unsecured Notes 4.68% 02/27/29 60,000 60,000 OTP Series 2019A Senior Unsecured Notes 3.07% 10/10/29 10,000 10,000 OTP Series 2020A Senior Unsecured Notes 3.22% 02/25/30 10,000 10,000 OTP Series 2020B Senior Unsecured Notes 3.22% 08/20/30 40,000 40,000 OTP Series 2007D Senior Unsecured Notes 6.47% 08/20/37 50,000 50,000 OTP Series 2019B Senior Unsecured Notes 3.52% 10/10/39 26,000 26,000 OTP Series 2020C Senior Unsecured Notes 3.62% 02/25/40 10,000 10,000 OTP Series 2013B Senior Unsecured Notes 5.47% 02/27/44 90,000 90,000 OTP Series 2018A Senior Unsecured Notes 4.07% 02/07/48 100,000 100,000 OTP Series 2019C Senior Unsecured Notes 3.82% 10/10/49 64,000 64,000 OTP Series 2020D Senior Unsecured Notes 3.92% 02/25/50 15,000 15,000 OTC PACE Note 2.54% 03/18/21 — 169 Total $ 767,000 $ 767,169 Less: Current Maturities Net of Unamortized Debt Issuance Costs 169,962 140,087 Unamortized Long-Term Debt Issuance Costs 2,419 2,650 Total Long-Term Debt Net of Unamortized Debt Issuance Costs $ 594,619 $ 624,432 On June 10, 2021, OTP entered into a Note Purchase Agreement pursuant to which OTP agreed to issue, in a private placement transaction, $230 million aggregate principal amount of senior unsecured notes consisting of (a) $40 million of 2.74% Series 2021A Senior Unsecured Notes due November 29, 2031, (b) $100 million of 3.69% Series 2021B Senior Unsecured Notes due November 29, 2051 and (c) $90 million of 3.77% Series 2022A Senior Unsecured Notes due May 20, 2052. As of September 30, 2021, there were no amounts outstanding. The funding of the notes will occur in two issuances, $140 million in November 2021 and $90 million in May 2022. The issuance of the notes is subject to the satisfaction of certain customary conditions to closing. Financial Covenants Certain of OTC's and OTP's short-term and long-term debt agreements require the borrower, whether OTC or OTP, to maintain certain financial covenants, including a maximum debt to total capitalization ratio of 0.60 to 1.00, a minimum interest and dividend coverage ratio of 1.50 to 1.00, and a maximum level of priority indebtedness. As of September 30, 2021, OTC and OTP were in compliance with these financial covenants.

Pension Plan and Other Postreti

Pension Plan and Other Postretirement Benefits	9 Months Ended
	Sep. 30, 2021
Retirement Benefits [Abstract]
Pension Plan and Other Postretirement Benefits	Pension Plan and Other Postretirement Benefits Pension Plan Components of net periodic pension benefit cost for the three and nine months ended September 30, 2021 and 2020 are as follows: Three Months Ended September 30, Nine Months Ended September 30, (in thousands) 2021 2020 2021 2020 Service Cost–Benefit Earned During the Period $ 1,866 $ 1,655 $ 5,597 $ 4,966 Interest Cost on Projected Benefit Obligation 2,915 3,264 8,745 9,790 Expected Return on Assets (5,590) (5,506) (16,769) (16,516) Amortization of Net Actuarial Loss: From Regulatory Asset 2,660 2,231 7,981 6,693 From Other Comprehensive Income 68 55 204 165 Net Periodic Pension Cost $ 1,919 $ 1,699 $ 5,758 $ 5,098 We had no minimum funding requirement as of December 31, 2020 but made a discretionary plan contribution of $10.0 million in January 2021. Executive Survivor and Supplemental Retirement Plan (ESSRP) Components of net periodic pension benefit cost for the three and nine months ended September 30, 2021 and 2020 are as follows: Three Months Ended September 30, Nine Months Ended September 30, (in thousands) 2021 2020 2021 2020 Service Cost–Benefit Earned During the Period $ 47 $ 45 $ 140 $ 134 Interest Cost on Projected Benefit Obligation 307 362 921 1,086 Amortization of Net Actuarial Loss: From Regulatory Asset 30 24 92 71 From Other Comprehensive Income 124 85 373 256 Net Periodic Pension Cost $ 508 $ 516 $ 1,526 $ 1,547 Other Postretirement Benefits Components of net periodic postretirement benefit cost for the three and nine months ended September 30, 2021 and 2020 are as follows: Three Months Ended September 30, Nine Months Ended September 30, (in thousands) 2021 2020 2021 2020 Service Cost–Benefit Earned During the Period $ 430 $ 461 $ 1,291 $ 1,385 Interest Cost on Projected Benefit Obligation 472 598 1,418 1,795 Amortization of Prior Service Cost From Regulatory Asset (1,397) (1,169) (4,192) (3,508) From Other Comprehensive Income (35) (28) (107) (86) Amortization of Net Actuarial Loss From Regulatory Asset 919 1,051 2,759 3,154 From Other Comprehensive Income 24 26 71 78 Net Periodic Postretirement Benefit Cost $ 413 $ 939 $ 1,240 $ 2,818

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The reconciliation of the statutory federal income tax rate to our effective tax rate for each of the three and nine months ended September 30, 2021 and 2020 is as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Federal Statutory Rate 21.0 % 21.0 % 21.0 % 21.0 % Increases (Decreases) in Tax from: State Taxes on Income, Net of Federal Tax 5.0 5.0 5.0 5.0 Production Tax Credits (PTCs) (5.0) — (6.0) — Amortization of Excess Deferred Income Taxes (1.6) (2.9) (2.0) (3.4) North Dakota Wind Tax Credit Amortization, Net of Federal Tax (0.2) (0.6) (0.3) (0.8) Excess Tax Deduction on Stock Awards — 0.3 — (0.4) Allowance for Equity Funds Used During Construction (0.1) (0.7) (0.1) (0.8) Other, Net (0.8) (1.9) (0.7) (1.2) Effective Tax Rate 18.3 % 20.2 % 16.9 % 19.4 % We began generating PTCs from our Merricourt wind farm placed in service in the fourth quarter of 2020. No PTCs were generated during the nine months ended September 30, 2020. Income tax benefits arising from PTCs are offset by corresponding operating revenue reductions.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Commitments Construction and Other Purchase Commitments. OTP has commitments under contracts, including its share of construction program and other commitments associated with its jointly-owned facilities, extending into 2046. Electric Utility Capacity and Energy Requirements and Coal Purchase and Delivery Contracts. OTP has commitments for the purchase of capacity and energy requirements under agreements extending into 2044. OTP also has contracts providing for the purchase and delivery of a significant portion of its current coal requirements, with expiration dates ranging from 2022 through 2040. Certain contracts do not include minimum purchase requirements but do require all coal necessary for the operation of the respective plant to be purchased from the counterparty. Land Easements. OTP has commitments to make future payments under land easements extending into 2050. Contingencies FERC ROE. In November 2013 and February 2015, customers filed complaints with FERC seeking to reduce the ROE component of the transmission rates that MISO transmission owners, including OTP, may collect under the MISO tariff rate. FERC's most recent order, issued on November 19, 2020, adopted a revised ROE methodology and set the base ROE at 10.02% (10.52% with an adder) effective for the fifteen-month period from November 2013 to February 2015 and on a prospective basis beginning in September 2016. The order also dismissed any complaints covering the period from February 2015 to May 2016. The November 2020 opinion is subject to judicial review. We have deferred recognition and recorded a refund liability of $3.0 million as of September 30, 2021. This refund liability reflects our best estimate of required refunds to customers once all regulatory and judicial proceedings are completed. Regional Haze Rule (RHR). The RHR was adopted in an effort to improve visibility in national parks and wilderness areas. The RHR requires states, in coordination with the EPA and other governmental agencies, to develop and implement plans to achieve natural visibility conditions. The second RHR implementation period covers the years 2018-2028. States are required to submit a state implementation plan to assess reasonable progress with the RHR and determine what additional emission reductions are appropriate, if any. Coyote Station, OTP's jointly owned coal-fired power plant in North Dakota, is subject to assessment in the second implementation period under the North Dakota state implementation plan. In September 2021, the North Dakota Department of Environmental Quality (NDDEQ) made public a draft of its state implementation plan. The plan concluded it is not reasonable to require additional emission controls during this planning period. Following a consultation and public comment period, and any subsequent modifications to the plan, the NDDEQ will submit its state implementation plan to the EPA for approval. We cannot predict with certainty the impact the state implementation plan may have on our business until the state implementation plan has been approved or otherwise acted on by the EPA. However, significant emission control investments could be required and the recovery of such costs from customers would require regulatory approval. Alternatively, investments in emission control equipment may prove to be uneconomic and result in an early retirement of, or the sale of our interest in, Coyote Station, subject to regulatory approval. We cannot estimate the financial effects such a retirement or sale may have on our consolidated operating results, financial position or cash flows, but such amounts could be material and the recovery of such costs from customers would be subject to regulatory approval. Westmoreland Coal Company (Westmoreland) Arbitration. In December 2018, insurers for Westmoreland, Westmoreland and its affiliated companies filed an arbitration demand against the co-owners of Coyote Station, including OTP, a 35% co-owner. The claimant insurers are pursuing recovery in the amount of $5.5 million, plus prejudgment interest to recover business interruption insurance proceeds paid to Westmoreland or its affiliates arising from a boiler feed pump explosion in December 2014 at the facility. The explosion and ensuing repairs reduced the amount of coal purchased from a Westmoreland affiliate under an existing coal purchase agreement. The Westmoreland insurers claim the co-owners breached the minimum purchase obligations in the coal purchase agreement. As of September 30, 2021, we have recorded an estimated liability for losses to be incurred related to this matter based upon the most recent information available, however, ultimate losses could be in excess of the amount recorded. Any losses incurred from this matter could be eligible for recovery through typical cost recovery processes of our electric utility business. The potential cost recovery would be subject to regulatory approval. Other Contingencies. We are party to litigation and regulatory matters arising in the normal course of business. We regularly analyze relevant information and, as necessary, estimate and record accrued liabilities for legal, regulatory enforcement and other matters in which a loss is probable of occurring and can be reasonably estimated. We believe the effect on our consolidated operating results, financial position and cash flows, if any, for the disposition of all matters pending as of September 30, 2021, other than those discussed above, will not be material.

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Stockholders' Equity	Stockholders' Equity Registration Statements On May 3, 2021 we filed a shelf registration statement with the Securities and Exchange Commission (SEC) under which we may offer for sale, from time to time, either separately or together in any combination, equity, debt or other securities described in the shelf registration statement. The registration statement expires in May 2024. On May 3, 2021, we filed a second registration statement with the SEC for the issuance of up to 1,500,000 common shares under an Automatic Dividend Reinvestment and Share Purchase Plan, which provides shareholders, retail customers of OTP and other interested investors a method of purchasing our common shares by reinvesting their dividends and/or making optional cash investments. Shares purchased under the plan may be new issue common shares or common shares purchased on the open market. The registration statement expires in May 2024. Dividend Restrictions Otter Tail Corporation is a holding company with no significant operations of its own. The primary source of funds for payments of dividends to our shareholders is from dividends paid or distributions made by our subsidiaries. As a result of certain statutory limitations or regulatory or financing agreements, restrictions could occur on the amount of distributions allowed to be made by our subsidiaries. Both the OTC Credit Agreement and OTP Credit Agreement contain restrictions on the payment of cash dividends upon a default or event of default, including failure to maintain certain financial covenants. As of September 30, 2021, we were in compliance with these financial covenants. Under the Federal Power Act, a public utility may not pay dividends from any funds properly included in a capital account. What constitutes “funds properly included in a capital account” is undefined in the Federal Power Act or the related regulations; however, the FERC has consistently interpreted the provision to allow dividends to be paid as long as i) the source of the dividends is clearly disclosed, ii) the dividend is not excessive and iii) there is no self-dealing on the part of corporate officials.

Share-Based Payments

Share-Based Payments	9 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement [Abstract]
Share-Based Payments	Share-Based Payments Stock Compensation Expense Stock-based compensation expense arising from our employee stock purchase plan and share-based compensation plans, recognized within operating expenses in the consolidated statements of income, amounted to $0.8 million and $1.3 million for the three months ended September 30, 2021 and 2020, respectively, and $6.4 million and $5.3 million for the nine months ended September 30, 2021 and 2020, respectively. Stock Awards. We grant restricted stock awards to members of our Board of Directors and restricted stock units to our employees. The awards vest, depending on award type and recipient, either ratably over periods of three The grant date fair value of each stock award is determined based on the market price of our common stock on the date of grant adjusted to exclude the value of dividends for those awards that do not receive dividend or dividend equivalent payments during the vesting period. The following is a summary of stock award activity for the nine months ended September 30, 2021: Shares Weighted Average Nonvested, January 1, 2021 128,664 $ 44.30 Granted 57,650 43.10 Vested (47,646) 42.98 Forfeited (2,075) 40.95 Nonvested, September 30, 2021 136,593 $ 44.30 The fair value of vested awards was $2.1 million and $2.8 million during the nine months ended September 30, 2021 and 2020. Stock Performance Awards. Stock performance awards are granted to executive officers and certain other key employees. The awards vest at the end of a three-year performance period. The number of common shares awarded, if any, at the end of the performance period ranges from zero to 150% of the target amount based on two performance measures: i) total shareholder return relative to a peer group and ii) return on equity. The awards have no voting or dividend rights during the vesting period. Vesting of the awards is accelerated in certain circumstances, including on retirement. The amount of common shares awarded on an accelerated vesting is based either on actual performance at the end of the performance period or the amount of common shares earned at target. The grant date fair value of stock performance awards granted during the nine months ended September 30, 2021 and 2020 was determined using a Monte Carlo fair value simulation model incorporating the following assumptions: 2021 2020 Risk-free interest rate 0.18 % 1.42 % Expected term (in years) 3.00 3.00 Expected volatility 32.00 % 19.00 % Dividend yield 3.60 % 2.80 % The risk-free interest rate was derived from yields on U.S. government bonds of a similar term. The expected term of the award is equal to the three-year performance period. Expected volatility was estimated based on actual historical volatility of our common stock. Dividend yield was estimated based on historic and future yield estimates. The following is a summary of stock performance award activity for the nine months ended September 30, 2021 (share amounts reflect awards at target): Shares Weighted Average Nonvested, January 1, 2021 164,600 $ 42.32 Granted 79,000 38.34 Vested (54,000) 35.73 Forfeited — — Nonvested, September 30, 2021 189,600 $ 42.54

Earnings Per Share

Earnings Per Share	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Earnings Per Share	Earnings Per ShareThe numerator used in the calculation of both basic and diluted earnings per common share is net income. The denominator used in the calculation of basic earnings per common share is the weighted average number of common shares outstanding during the period. The denominator used in the calculation of diluted earnings per common share is derived by adjusting basic shares outstanding for the dilutive effect of potential common shares outstanding, which consist of time and performance based stock awards and employee stock purchase plan shares. The following includes the computation of the denominator for basic and diluted weighted-average shares outstanding for the three and nine months ended September 30, 2021 and 2020: Three Months Ended September 30, Nine Months Ended September 30, (in thousands) 2021 2020 2021 2020 Weighted Average Common Shares Outstanding – Basic 41,504 40,914 41,487 40,548 Effect of Dilutive Securities: Stock Performance Awards 262 98 209 107 Stock Awards 88 49 82 53 Employee Stock Purchase Plan Shares and Other 15 17 17 25 Dilutive Effect of Potential Common Shares 365 164 308 185 Weighted Average Common Shares Outstanding – Diluted 41,869 41,078 41,795 40,733 The amount of shares excluded from diluted weighted-average common shares outstanding because such shares were anti-dilutive was not material for the three and nine months ended September 30, 2021 and 2020.

Derivative Instruments

Derivative Instruments	9 Months Ended
	Sep. 30, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments	Derivative Instruments OTP enters into derivative instruments to manage its exposure to future price variability and reduce volatility in prices for our retail customers. These derivative instruments are not designated as qualifying hedging transactions but provide for an economic hedge against future price variability. The instruments are recorded at fair value on the consolidated balance sheets, with changes in fair value recorded in the consolidated statements of income. However, in accordance with rate-making and cost recovery processes, we recognize a regulatory asset or liability to defer losses or gains from derivative activity until settlement of the associated derivative instrument. As of September 30, 2021, OTP had outstanding pay-fixed, receive-variable swap agreements with an aggregate notional amount of 356,200 megawatt-hours of electricity, which will be settled periodically through 2022. As of September 30, 2021, the aggregate fair value of these contracts was $6.9 million, of which $6.1 million is included in other current assets and $0.8 million is included in other noncurrent assets on the consolidated balance sheets.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The following tables present our assets measured at fair value on a recurring basis as of September 30, 2021 and December 31, 2020 classified by the input method used to measure fair value: Level 1 Level 2 Level 3 September 30, 2021 Investments: Money Market Funds $ 953 $ — $ — Mutual Funds 5,170 — — Corporate Debt Securities — 2,377 — Government-Backed and Government-Sponsored Enterprises’ Debt Securities — 6,831 — Derivative Instruments — 6,923 — Total Assets $ 6,123 $ 16,131 $ — December 31, 2020 Investments: Money Market Funds $ 4,075 $ — $ — Mutual Funds 1,662 — — Corporate Debt Securities — 2,627 — Government-Backed and Government-Sponsored Enterprises’ Debt Securities — 6,633 — Total Assets $ 5,737 $ 9,260 $ — The level 2 fair value measurements for government-backed and government-sponsored enterprises and corporate debt securities are determined on the basis of valuations provided by a third-party pricing service which utilizes industry accepted valuation models and observable market inputs to determine valuation. Some valuations or model inputs used by the pricing service may be based on broker quotes. The level 2 fair value measurements for derivative instruments are determined by using inputs such as forward electric commodity prices, adjusted for location differences. These inputs are observable in the marketplace throughout the full term of the instrument, can be derived from observable data, or are supported by observable levels at which transactions are executed in the marketplace. In addition to assets recorded at fair value on a recurring basis, we also hold financial instruments that are not recorded at fair value in the consolidated balance sheets but for which disclosure of the fair value of these financial instruments is provided. The following reflects the carrying value and estimated fair value of these assets and liabilities as of September 30, 2021 and December 31, 2020: September 30, 2021 December 31, 2020 (in thousands) Carrying Fair Value Carrying Fair Value Assets: Cash and Cash Equivalents $ 1,272 $ 1,272 $ 1,163 $ 1,163 Total 1,272 1,272 1,163 1,163 Liabilities: Short-Term Debt 97,857 97,857 80,997 80,997 Long-Term Debt 764,581 873,632 764,519 858,455 Total $ 862,438 $ 971,489 $ 845,516 $ 939,452 The following methods and assumptions were used to estimate the fair value of each class of financial instruments for which it is practicable to estimate that value: Cash Equivalents: The carrying amount approximates fair value because of the short-term maturity of those instruments. Short-Term Debt: The carrying amount approximates fair value because the debt obligations are short-term and the balances outstanding are subject to variable rates of interest which reset frequently, a Level 2 fair value input. Long-Term Debt: The fair value of long-term debt is estimated based on current market indications for borrowings of similar maturities, a Level 2 fair value input.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The unaudited consolidated financial statements included herein have been prepared pursuant to the rules and regulations of the SEC for interim reporting. Accordingly, they do not include all the information and footnotes required by generally accepted accounting principles. In the opinion of management, we have included all adjustments, including normal recurring accruals, necessary for a fair presentation of the consolidated financial statements for the periods presented. The consolidated financial statements and condensed notes thereto should be read in conjunction with the consolidated financial statements and notes included in our Annual Report on Form 10-K for the fiscal year ended December 31, 2020. Because of the coronavirus (COVID-19) pandemic, the seasonality of our businesses and other factors, the earnings for the three and nine months ended September 30, 2021 should not be taken as an indication of earnings for all or any part of the balance of the current year or as an indication of earnings for future years.
Use of Estimates	Use of Estimates We use estimates based on the best information available in recording transactions and balances resulting from business operations. As better information becomes available, or actual amounts are known, the recorded estimates are revised. Consequently, operating results can be affected by revisions to prior accounting estimates.

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2021
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	Information for each segment and our unallocated corporate costs for the three and nine months ended September 30, 2021 and 2020 are as follows: Three Months Ended September 30, Nine Months Ended September 30, (in thousands) 2021 2020 2021 2020 Operating Revenue 1 Electric $ 118,775 $ 115,213 $ 348,629 $ 333,213 Manufacturing 89,977 59,849 250,085 174,276 Plastics 107,542 60,693 264,898 155,769 Total $ 316,294 $ 235,755 $ 863,612 $ 663,258 Net Income (Loss) Electric $ 22,528 $ 24,737 $ 55,547 $ 54,225 Manufacturing 4,200 3,311 15,290 8,476 Plastics 28,410 10,343 60,102 20,922 Corporate (2,384) (2,457) (5,787) (6,440) Total $ 52,754 $ 35,934 $ 125,152 $ 77,183 1 Amounts reflect operating revenues to external customers. Intersegment operating revenues are not material for any period presented. The following provides the identifiable assets by segment and corporate assets as of September 30, 2021 and December 31, 2020: (in thousands) September 30, December 31, Identifiable Assets Electric $ 2,271,636 $ 2,233,399 Manufacturing 242,414 191,005 Plastics 143,615 99,767 Corporate 55,483 54,183 Total $ 2,713,148 $ 2,578,354

Revenue (Tables)

Revenue (Tables)	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	We present our operating revenues to external customers, in total and by amounts arising from contracts with customers and alternative revenue program (ARP) arrangements, disaggregated by revenue source and segment for the three and nine months ended September 30, 2021 and 2020: Three Months Ended September 30, Nine Months Ended September 30, (in thousands) 2021 2020 2021 2020 Operating Revenues Electric Segment Retail: Residential $ 33,902 $ 32,734 $ 100,067 $ 96,440 Retail: Commercial and Industrial 60,557 64,918 185,376 189,771 Retail: Other 1,979 1,953 5,687 5,550 Total Retail 96,438 99,605 291,130 291,761 Transmission 13,300 12,288 37,085 32,802 Wholesale 6,944 1,500 14,711 3,141 Other 2,093 1,820 5,703 5,509 Total Electric Segment 118,775 115,213 348,629 333,213 Manufacturing Segment Metal Parts and Tooling 76,455 50,957 210,141 145,435 Plastic Products and Tooling 10,198 7,600 30,624 25,323 Scrap Metal Sales 3,324 1,292 9,320 3,518 Total Manufacturing Segment 89,977 59,849 250,085 174,276 Plastics Segment PVC Pipe 107,542 60,693 264,898 155,769 Total Operating Revenue 316,294 235,755 863,612 663,258 Less: Non-contract Revenues Included Above Electric Segment - ARP Revenues (33) 2,778 (2,790) 2,900 Total Operating Revenues from Contracts with Customers $ 316,327 $ 232,977 $ 866,402 $ 660,358

Select Balance Sheet Informat_2

Select Balance Sheet Information (Tables)	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Receivables	Receivables as of September 30, 2021 and December 31, 2020 are as follows: (in thousands) September 30, December 31, Receivables Trade $ 152,906 $ 87,048 Other 11,182 8,939 Unbilled Receivables 17,003 21,187 Total Receivables 181,091 117,174 Less: Allowance for Credit Losses 2,332 3,215 Receivables, net of allowance for credit losses $ 178,759 $ 113,959
Summary of Activity in Allowance for Credit Losses	The following is a summary of activity in the allowance for credit losses for the nine months ended September 30, 2021 and 2020: (in thousands) 2021 2020 Beginning Balance, January 1 $ 3,215 $ 1,339 Additions Charged to Expense 177 1,845 Reductions for Amounts Written Off, Net of Recoveries (1,060) (923) Ending Balance, September 30 $ 2,332 $ 2,261
Schedule of Inventories	Inventories consist of the following as of September 30, 2021 and December 31, 2020: (in thousands) September 30, December 31, Finished Goods $ 25,727 $ 22,046 Work in Process 29,932 16,210 Raw Material, Fuel and Supplies 58,956 53,909 Total Inventories $ 114,615 $ 92,165
Schedule of Investments	The following is a summary of our investments as of September 30, 2021 and December 31, 2020: (in thousands) September 30, December 31, Corporate-Owned Life Insurance Policies $ 40,096 $ 36,825 Debt Securities 9,208 9,260 Money Market Funds 953 4,075 Mutual Funds 5,170 1,662 Other Investments 29 34 Total Investments $ 55,456 $ 51,856
Schedule of Property, Plant and Equipment	Major classes of property, plant and equipment as of September 30, 2021 and December 31, 2020 include: (in thousands) September 30, December 31, Electric Plant in Service Electric Plant in Service $ 2,705,778 $ 2,531,352 Construction Work in Progress 100,495 203,078 Total Gross Electric Plant 2,806,273 2,734,430 Less Accumulated Depreciation and Amortization 822,441 778,988 Net Electric Plant 1,983,832 1,955,442 Nonelectric Property, Plant and Equipment Nonelectric Property, Plant and Equipment in Service 263,880 258,730 Construction Work in Progress 15,564 9,290 Total Gross Nonelectric Property, Plant and Equipment 279,444 268,020 Less Accumulated Depreciation and Amortization 180,053 174,189 Net Nonelectric Property, Plant and Equipment 99,391 93,831 Net Property, Plant and Equipment $ 2,083,223 $ 2,049,273

Regulatory Matters (Tables)

Regulatory Matters (Tables)	9 Months Ended
	Sep. 30, 2021
Regulatory Assets and Liabilities Disclosure [Abstract]
Schedule of Regulatory Assets and Liabilities	The following presents our current and long-term regulatory assets and liabilities as of September 30, 2021 and December 31, 2020 and the period we expect to recover or refund such amounts: Period of September 30, 2021 December 31, 2020 (in thousands) Recovery/Refund Current Long-Term Current Long Term Regulatory Assets Pension and Other Postretirement Benefit Plans 1 Various $ 11,037 $ 139,467 $ 11,037 $ 146,071 Alternative Revenue Program Riders 2 Up to 3 years 7,229 8,225 8,871 9,373 Asset Retirement Obligations 1 Asset lives — 7,065 — 8,462 ISO Cost Recovery Trackers 1 Up to 2 years 270 1,027 1,079 867 Unrecovered Project Costs 1 Up to 3 years 3,227 1,456 361 2,989 Deferred Rate Case Expenses 1 Various 637 936 360 230 Debt Reacquisition Premiums 1 Up to 12 years 117 262 192 341 Other 1 Various — 77 — 62 Total Regulatory Assets $ 22,517 $ 158,515 $ 21,900 $ 168,395 Regulatory Liabilities Deferred Income Taxes Asset lives $ — $ 130,555 $ — $ 134,719 Plant Removal Obligations Asset lives 5,893 96,734 — 98,707 Fuel Clause Adjustments Up to 1 year 5,692 — 10,947 — Alternative Revenue Program Riders Various 5,265 2,507 3,581 470 Pension and Other Postretirement Benefit Plans Up to 1 year 1,959 — 1,959 — Derivative Instruments Various 6,136 787 — — Other Various 378 150 176 77 Total Regulatory Liabilities $ 25,323 $ 230,733 $ 16,663 $ 233,973 1 Costs subject to recovery without a rate of return. 2 Amount eligible for recovery includes an incentive or rate of return.

Short-Term and Long-Term Borr_2

Short-Term and Long-Term Borrowings (Tables)	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Schedule of Line of Credit Facilities	The following is a summary of our lines of credit as of September 30, 2021 and December 31, 2020: September 30, 2021 December 31, (in thousands) Line Limit Amount Outstanding Letters Amount Available Amount Available OTC Credit Agreement $ 170,000 $ 36,624 $ — $ 133,376 $ 104,834 OTP Credit Agreement 170,000 61,233 13,159 95,608 140,068 Total $ 340,000 $ 97,857 $ 13,159 $ 228,984 $ 244,902
Schedule of Debt	The following is a summary of outstanding long-term debt by borrower as of September 30, 2021 and December 31, 2020: (in thousands) Entity Debt Instrument Rate Maturity September 30, December 31, OTC Guaranteed Senior Notes 3.55% 12/15/26 $ 80,000 $ 80,000 OTP Series 2011A Senior Unsecured Notes 4.63% 12/01/21 140,000 140,000 OTP Series 2007B Senior Unsecured Notes 6.15% 08/20/22 30,000 30,000 OTP Series 2007C Senior Unsecured Notes 6.37% 08/02/27 42,000 42,000 OTP Series 2013A Senior Unsecured Notes 4.68% 02/27/29 60,000 60,000 OTP Series 2019A Senior Unsecured Notes 3.07% 10/10/29 10,000 10,000 OTP Series 2020A Senior Unsecured Notes 3.22% 02/25/30 10,000 10,000 OTP Series 2020B Senior Unsecured Notes 3.22% 08/20/30 40,000 40,000 OTP Series 2007D Senior Unsecured Notes 6.47% 08/20/37 50,000 50,000 OTP Series 2019B Senior Unsecured Notes 3.52% 10/10/39 26,000 26,000 OTP Series 2020C Senior Unsecured Notes 3.62% 02/25/40 10,000 10,000 OTP Series 2013B Senior Unsecured Notes 5.47% 02/27/44 90,000 90,000 OTP Series 2018A Senior Unsecured Notes 4.07% 02/07/48 100,000 100,000 OTP Series 2019C Senior Unsecured Notes 3.82% 10/10/49 64,000 64,000 OTP Series 2020D Senior Unsecured Notes 3.92% 02/25/50 15,000 15,000 OTC PACE Note 2.54% 03/18/21 — 169 Total $ 767,000 $ 767,169 Less: Current Maturities Net of Unamortized Debt Issuance Costs 169,962 140,087 Unamortized Long-Term Debt Issuance Costs 2,419 2,650 Total Long-Term Debt Net of Unamortized Debt Issuance Costs $ 594,619 $ 624,432

Pension Plan and Other Postre_2

Pension Plan and Other Postretirement Benefits (Tables)	9 Months Ended
	Sep. 30, 2021
Retirement Benefits [Abstract]
Schedule of Net Benefit Costs	Components of net periodic pension benefit cost for the three and nine months ended September 30, 2021 and 2020 are as follows: Three Months Ended September 30, Nine Months Ended September 30, (in thousands) 2021 2020 2021 2020 Service Cost–Benefit Earned During the Period $ 1,866 $ 1,655 $ 5,597 $ 4,966 Interest Cost on Projected Benefit Obligation 2,915 3,264 8,745 9,790 Expected Return on Assets (5,590) (5,506) (16,769) (16,516) Amortization of Net Actuarial Loss: From Regulatory Asset 2,660 2,231 7,981 6,693 From Other Comprehensive Income 68 55 204 165 Net Periodic Pension Cost $ 1,919 $ 1,699 $ 5,758 $ 5,098 Components of net periodic pension benefit cost for the three and nine months ended September 30, 2021 and 2020 are as follows: Three Months Ended September 30, Nine Months Ended September 30, (in thousands) 2021 2020 2021 2020 Service Cost–Benefit Earned During the Period $ 47 $ 45 $ 140 $ 134 Interest Cost on Projected Benefit Obligation 307 362 921 1,086 Amortization of Net Actuarial Loss: From Regulatory Asset 30 24 92 71 From Other Comprehensive Income 124 85 373 256 Net Periodic Pension Cost $ 508 $ 516 $ 1,526 $ 1,547 Components of net periodic postretirement benefit cost for the three and nine months ended September 30, 2021 and 2020 are as follows: Three Months Ended September 30, Nine Months Ended September 30, (in thousands) 2021 2020 2021 2020 Service Cost–Benefit Earned During the Period $ 430 $ 461 $ 1,291 $ 1,385 Interest Cost on Projected Benefit Obligation 472 598 1,418 1,795 Amortization of Prior Service Cost From Regulatory Asset (1,397) (1,169) (4,192) (3,508) From Other Comprehensive Income (35) (28) (107) (86) Amortization of Net Actuarial Loss From Regulatory Asset 919 1,051 2,759 3,154 From Other Comprehensive Income 24 26 71 78 Net Periodic Postretirement Benefit Cost $ 413 $ 939 $ 1,240 $ 2,818

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Schedule of Effective Income Tax Rate Reconciliation	The reconciliation of the statutory federal income tax rate to our effective tax rate for each of the three and nine months ended September 30, 2021 and 2020 is as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Federal Statutory Rate 21.0 % 21.0 % 21.0 % 21.0 % Increases (Decreases) in Tax from: State Taxes on Income, Net of Federal Tax 5.0 5.0 5.0 5.0 Production Tax Credits (PTCs) (5.0) — (6.0) — Amortization of Excess Deferred Income Taxes (1.6) (2.9) (2.0) (3.4) North Dakota Wind Tax Credit Amortization, Net of Federal Tax (0.2) (0.6) (0.3) (0.8) Excess Tax Deduction on Stock Awards — 0.3 — (0.4) Allowance for Equity Funds Used During Construction (0.1) (0.7) (0.1) (0.8) Other, Net (0.8) (1.9) (0.7) (1.2) Effective Tax Rate 18.3 % 20.2 % 16.9 % 19.4 %

Share-Based Payments (Tables)

Share-Based Payments (Tables)	9 Months Ended
	Sep. 30, 2021
Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Share-based Compensation Arrangements by Share-based Payment Award	The following is a summary of stock award activity for the nine months ended September 30, 2021: Shares Weighted Average Nonvested, January 1, 2021 128,664 $ 44.30 Granted 57,650 43.10 Vested (47,646) 42.98 Forfeited (2,075) 40.95 Nonvested, September 30, 2021 136,593 $ 44.30
Stock Performance Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Share-based Compensation Arrangements by Share-based Payment Award	The following is a summary of stock performance award activity for the nine months ended September 30, 2021 (share amounts reflect awards at target): Shares Weighted Average Nonvested, January 1, 2021 164,600 $ 42.32 Granted 79,000 38.34 Vested (54,000) 35.73 Forfeited — — Nonvested, September 30, 2021 189,600 $ 42.54
Schedule of Weighted-Average Assumptions	The grant date fair value of stock performance awards granted during the nine months ended September 30, 2021 and 2020 was determined using a Monte Carlo fair value simulation model incorporating the following assumptions: 2021 2020 Risk-free interest rate 0.18 % 1.42 % Expected term (in years) 3.00 3.00 Expected volatility 32.00 % 19.00 % Dividend yield 3.60 % 2.80 %

Earnings Per Share (Tables)

Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	The following includes the computation of the denominator for basic and diluted weighted-average shares outstanding for the three and nine months ended September 30, 2021 and 2020: Three Months Ended September 30, Nine Months Ended September 30, (in thousands) 2021 2020 2021 2020 Weighted Average Common Shares Outstanding – Basic 41,504 40,914 41,487 40,548 Effect of Dilutive Securities: Stock Performance Awards 262 98 209 107 Stock Awards 88 49 82 53 Employee Stock Purchase Plan Shares and Other 15 17 17 25 Dilutive Effect of Potential Common Shares 365 164 308 185 Weighted Average Common Shares Outstanding – Diluted 41,869 41,078 41,795 40,733

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Schedule of Fair Value Measurements, Recurring and Nonrecurring	The following tables present our assets measured at fair value on a recurring basis as of September 30, 2021 and December 31, 2020 classified by the input method used to measure fair value: Level 1 Level 2 Level 3 September 30, 2021 Investments: Money Market Funds $ 953 $ — $ — Mutual Funds 5,170 — — Corporate Debt Securities — 2,377 — Government-Backed and Government-Sponsored Enterprises’ Debt Securities — 6,831 — Derivative Instruments — 6,923 — Total Assets $ 6,123 $ 16,131 $ — December 31, 2020 Investments: Money Market Funds $ 4,075 $ — $ — Mutual Funds 1,662 — — Corporate Debt Securities — 2,627 — Government-Backed and Government-Sponsored Enterprises’ Debt Securities — 6,633 — Total Assets $ 5,737 $ 9,260 $ —
Schedule of Fair Value of Assets and Liabilities	The following reflects the carrying value and estimated fair value of these assets and liabilities as of September 30, 2021 and December 31, 2020: September 30, 2021 December 31, 2020 (in thousands) Carrying Fair Value Carrying Fair Value Assets: Cash and Cash Equivalents $ 1,272 $ 1,272 $ 1,163 $ 1,163 Total 1,272 1,272 1,163 1,163 Liabilities: Short-Term Debt 97,857 97,857 80,997 80,997 Long-Term Debt 764,581 873,632 764,519 858,455 Total $ 862,438 $ 971,489 $ 845,516 $ 939,452

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Details)	9 Months Ended
	Sep. 30, 2021segment
Accounting Policies [Abstract]
Number of operating segments	3

Segment Information - Narrative

Segment Information - Narrative (Details)	9 Months Ended
	Sep. 30, 2021segment
Segment Reporting [Abstract]
Number of reportable segments	3

Segment Information - Business

Segment Information - Business Segments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Total Operating Revenues	$ 316,294	$ 235,755	$ 863,612	$ 663,258
Net Income (Loss)	52,754	35,934	125,152	77,183
Identifiable Assets	2,713,148		2,713,148		$ 2,578,354
Corporate
Segment Reporting Information [Line Items]
Net Income (Loss)	(2,384)	(2,457)	(5,787)	(6,440)
Identifiable Assets	55,483		55,483		54,183
Electric | Operating Segments
Segment Reporting Information [Line Items]
Total Operating Revenues	118,775	115,213	348,629	333,213
Net Income (Loss)	22,528	24,737	55,547	54,225
Identifiable Assets	2,271,636		2,271,636		2,233,399
Manufacturing | Operating Segments
Segment Reporting Information [Line Items]
Total Operating Revenues	89,977	59,849	250,085	174,276
Net Income (Loss)	4,200	3,311	15,290	8,476
Identifiable Assets	242,414		242,414		191,005
Plastics | Operating Segments
Segment Reporting Information [Line Items]
Total Operating Revenues	107,542	60,693	264,898	155,769
Net Income (Loss)	28,410	$ 10,343	60,102	$ 20,922
Identifiable Assets	$ 143,615		$ 143,615		$ 99,767

Revenue (Details)

Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Total Operating Revenues	$ 316,294	$ 235,755	$ 863,612	$ 663,258
Operating Segments
Disaggregation of Revenue [Line Items]
Total Operating Revenues from Contracts with Customers	316,327	232,977	866,402	660,358
Operating Segments | Electric
Disaggregation of Revenue [Line Items]
Total Operating Revenues	118,775	115,213	348,629	333,213
Electric Segment - ARP Revenues	(33)	2,778	(2,790)	2,900
Operating Segments | Manufacturing
Disaggregation of Revenue [Line Items]
Total Operating Revenues	89,977	59,849	250,085	174,276
Operating Segments | Plastics
Disaggregation of Revenue [Line Items]
Total Operating Revenues	107,542	60,693	264,898	155,769
Operating Segments | Retail: Residential | Electric
Disaggregation of Revenue [Line Items]
Total Operating Revenues	33,902	32,734	100,067	96,440
Operating Segments | Retail: Commercial and Industrial | Electric
Disaggregation of Revenue [Line Items]
Total Operating Revenues	60,557	64,918	185,376	189,771
Operating Segments | Retail: Other | Electric
Disaggregation of Revenue [Line Items]
Total Operating Revenues	1,979	1,953	5,687	5,550
Operating Segments | Total Retail | Electric
Disaggregation of Revenue [Line Items]
Total Operating Revenues	96,438	99,605	291,130	291,761
Operating Segments | Transmission | Electric
Disaggregation of Revenue [Line Items]
Total Operating Revenues	13,300	12,288	37,085	32,802
Operating Segments | Wholesale | Electric
Disaggregation of Revenue [Line Items]
Total Operating Revenues	6,944	1,500	14,711	3,141
Operating Segments | Other | Electric
Disaggregation of Revenue [Line Items]
Total Operating Revenues	2,093	1,820	5,703	5,509
Operating Segments | Metal Parts and Tooling | Manufacturing
Disaggregation of Revenue [Line Items]
Total Operating Revenues	76,455	50,957	210,141	145,435
Operating Segments | Plastic Products and Tooling | Manufacturing
Disaggregation of Revenue [Line Items]
Total Operating Revenues	10,198	7,600	30,624	25,323
Operating Segments | Scrap Metal Sales | Manufacturing
Disaggregation of Revenue [Line Items]
Total Operating Revenues	$ 3,324	$ 1,292	$ 9,320	$ 3,518

Select Balance Sheet Informat_3

Select Balance Sheet Information - Schedule of Receivables (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Trade	$ 152,906	$ 87,048
Other	11,182	8,939
Unbilled Receivables	17,003	21,187
Total Receivables	181,091	117,174
Less: Allowance for Credit Losses	2,332	3,215	$ 2,261	$ 1,339
Receivables, net of allowance for credit losses	$ 178,759	$ 113,959

Select Balance Sheet Informat_4

Select Balance Sheet Information - Summary of Activity in Allowance for Credit Losses (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance, January 1	$ 3,215	$ 1,339
Additions Charged to Expense	177	1,845
Reductions for Amounts Written Off, Net of Recoveries	(1,060)	(923)
Ending Balance, September 30	$ 2,332	$ 2,261

Select Balance Sheet Informat_5

Select Balance Sheet Information - Schedule of Inventories (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Finished Goods	$ 25,727	$ 22,046
Work in Process	29,932	16,210
Raw Material, Fuel and Supplies	58,956	53,909
Inventories	$ 114,615	$ 92,165

Select Balance Sheet Informat_6

Select Balance Sheet Information - Schedule of Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Corporate-Owned Life Insurance Policies	$ 40,096	$ 36,825
Debt Securities	9,208	9,260
Money Market Funds	953	4,075
Mutual Funds	5,170	1,662
Other Investments	29	34
Total Investments	$ 55,456	$ 51,856

Select Balance Sheet Informat_7

Select Balance Sheet Information - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, net of accumulated depreciation	$ 2,083,223	$ 2,049,273
Electric Plant in Service
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,806,273	2,734,430
Less Accumulated Depreciation and Amortization	822,441	778,988
Property, Plant and Equipment, net of accumulated depreciation	1,983,832	1,955,442
Nonelectric Property, Plant and Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	279,444	268,020
Less Accumulated Depreciation and Amortization	180,053	174,189
Property, Plant and Equipment, net of accumulated depreciation	99,391	93,831
Electric Plant in Service | Electric Plant in Service
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,705,778	2,531,352
Construction Work in Progress | Electric Plant in Service
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	100,495	203,078
Construction Work in Progress | Nonelectric Property, Plant and Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	15,564	9,290
Nonelectric Property, Plant and Equipment in Service | Nonelectric Property, Plant and Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 263,880	$ 258,730

Regulatory Matters - Regulatory

Regulatory Matters - Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	$ 22,517	$ 21,900
Regulatory assets, long-term	158,515	168,395
Regulatory liabilities, current	25,323	16,663
Regulatory liabilities, long -term	230,733	233,973
Deferred Income Taxes
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities, current	0	0
Regulatory liabilities, long -term	130,555	134,719
Plant Removal Obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities, current	5,893	0
Regulatory liabilities, long -term	96,734	98,707
Fuel Clause Adjustments
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities, current	5,692	10,947
Regulatory liabilities, long -term	$ 0	0
Regulatory Liabilities - Remaining Recovery/Refund Period	1 year
Alternative Revenue Program Riders
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities, current	$ 5,265	3,581
Regulatory liabilities, long -term	2,507	470
Pension and Other Postretirement Benefit Plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities, current	1,959	1,959
Regulatory liabilities, long -term	$ 0	0
Regulatory Liabilities - Remaining Recovery/Refund Period	1 year
Derivative Instruments
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities, current	$ 6,136	0
Regulatory liabilities, long -term	787	0
Other
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities, current	378	176
Regulatory liabilities, long -term	150	77
Pension and Other Postretirement Benefit Plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	11,037	11,037
Regulatory assets, long-term	139,467	146,071
Alternative Revenue Program Riders
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	7,229	8,871
Regulatory assets, long-term	$ 8,225	9,373
Regulatory Assets - Remaining Recovery/Refund Period	3 years
Asset Retirement Obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	$ 0	0
Regulatory assets, long-term	7,065	8,462
ISO Cost Recovery Trackers
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	270	1,079
Regulatory assets, long-term	$ 1,027	867
Regulatory Assets - Remaining Recovery/Refund Period	2 years
Unrecovered Project Costs
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	$ 3,227	361
Regulatory assets, long-term	$ 1,456	2,989
Regulatory Assets - Remaining Recovery/Refund Period	3 years
Deferred Rate Case Expenses
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	$ 637	360
Regulatory assets, long-term	936	230
Debt Reacquisition Premiums
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	117	192
Regulatory assets, long-term	$ 262	341
Regulatory Assets - Remaining Recovery/Refund Period	12 years
Other
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	$ 0	0
Regulatory assets, long-term	$ 77	$ 62

Short-Term and Long-Term Borr_3

Short-Term and Long-Term Borrowings - Lines of Credit (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Line of Credit Facility [Line Items]
Line Limit	$ 340,000,000	$ 340,000,000
Amount Outstanding	97,857,000	80,997,000
Letters of Credit	13,159,000
Amount Available	228,984,000	244,902,000
OTC Credit Agreement
Line of Credit Facility [Line Items]
Line Limit	170,000,000	170,000,000
Amount Outstanding	36,624,000
Letters of Credit	0
Amount Available	133,376,000	104,834,000
OTP Credit Agreement
Line of Credit Facility [Line Items]
Line Limit	170,000,000	170,000,000
Amount Outstanding	61,233,000
Letters of Credit	13,159,000
Amount Available	$ 95,608,000	$ 140,068,000

Short-Term and Long-Term Borr_4

Short-Term and Long-Term Borrowings - Breakdown of Outstanding Long-term Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Long-term debt	$ 767,000	$ 767,169
Current Maturities Net of Unamortized Debt Issuance Costs	169,962	140,087
Unamortized Long-Term Debt Issuance Costs	2,419	2,650
Total Long-Term Debt Net of Unamortized Debt Issuance Costs	$ 594,619	624,432
Guaranteed Senior Notes
Debt Instrument [Line Items]
Rate	3.55%
Long-term debt	$ 80,000	80,000
Series 2011A Senior Unsecured Notes
Debt Instrument [Line Items]
Rate	4.63%
Long-term debt	$ 140,000	140,000
Series 2007B Senior Unsecured Notes
Debt Instrument [Line Items]
Rate	6.15%
Long-term debt	$ 30,000	30,000
Series 2007C Senior Unsecured Notes
Debt Instrument [Line Items]
Rate	6.37%
Long-term debt	$ 42,000	42,000
Series 2013A Senior Unsecured Notes
Debt Instrument [Line Items]
Rate	4.68%
Long-term debt	$ 60,000	60,000
Series 2019A Senior Unsecured Notes
Debt Instrument [Line Items]
Rate	3.07%
Long-term debt	$ 10,000	10,000
Series 2020A Senior Unsecured Notes
Debt Instrument [Line Items]
Rate	3.22%
Long-term debt	$ 10,000	10,000
Series 2020B Senior Unsecured Notes
Debt Instrument [Line Items]
Rate	3.22%
Long-term debt	$ 40,000	40,000
Series 2007D Senior Unsecured Notes
Debt Instrument [Line Items]
Rate	6.47%
Long-term debt	$ 50,000	50,000
Series 2019B Senior Unsecured Notes
Debt Instrument [Line Items]
Rate	3.52%
Long-term debt	$ 26,000	26,000
Series 2020C Senior Unsecured Notes
Debt Instrument [Line Items]
Rate	3.62%
Long-term debt	$ 10,000	10,000
Series 2013B Senior Unsecured Notes
Debt Instrument [Line Items]
Rate	5.47%
Long-term debt	$ 90,000	90,000
Series 2018A Senior Unsecured Notes
Debt Instrument [Line Items]
Rate	4.07%
Long-term debt	$ 100,000	100,000
Series 2019C Senior Unsecured Notes
Debt Instrument [Line Items]
Rate	3.82%
Long-term debt	$ 64,000	64,000
Series 2020D Senior Unsecured Notes
Debt Instrument [Line Items]
Rate	3.92%
Long-term debt	$ 15,000	15,000
PACE Note
Debt Instrument [Line Items]
Rate	2.54%
Long-term debt	$ 0	$ 169

Short-Term and Long-Term Borr_5

Short-Term and Long-Term Borrowings - Narrative (Details)	1 Months Ended		9 Months Ended
	May 31, 2022USD ($)	Nov. 30, 2021USD ($)	Sep. 30, 2021USD ($)issuance	Jun. 10, 2021USD ($)	Dec. 31, 2020USD ($)
Debt Instrument [Line Items]
Line Limit			$ 340,000,000		$ 340,000,000
Long-term debt			767,000,000		767,169,000
Senior Notes
Debt Instrument [Line Items]
Aggregate principal amount				$ 230,000,000
Long-term debt			$ 0
Number of issuances | issuance			2
Senior Notes | Forecast
Debt Instrument [Line Items]
Proceeds from issuance of debt	$ 90,000,000	$ 140,000,000
OTC Credit Agreement
Debt Instrument [Line Items]
Line Limit			$ 170,000,000		170,000,000
Debt, weighted average interest rate (as a percent)			1.59%
OTC Credit Agreement | Revolving Credit Facility
Debt Instrument [Line Items]
Line Limit			$ 170,000,000
OTC Credit Agreement | Letter of Credit
Debt Instrument [Line Items]
Line Limit			40,000,000
Line of credit facility, increased current borrowing capacity, accordion provision			290,000,000
OTP Credit Agreement
Debt Instrument [Line Items]
Line Limit			$ 170,000,000		$ 170,000,000
Debt, weighted average interest rate (as a percent)			1.33%
OTP Credit Agreement | Revolving Credit Facility
Debt Instrument [Line Items]
Line Limit			$ 170,000,000
OTP Credit Agreement | Letter of Credit
Debt Instrument [Line Items]
Line Limit			50,000,000
Line of credit facility, increased current borrowing capacity, accordion provision			$ 250,000,000
Senior Unsecured Notes 2.74%, Series A, Due November 29, 2031 | Senior Notes
Debt Instrument [Line Items]
Aggregate principal amount				$ 40,000,000
Interest rate (as a percent)				2.74%
Senior Unsecured Notes 3.69%, Series B, Due November 29, 2051 | Senior Notes
Debt Instrument [Line Items]
Aggregate principal amount				$ 100,000,000
Interest rate (as a percent)				3.69%
Senior Unsecured Notes 3.77%, Series A, Due May 20, 2052 | Senior Notes
Debt Instrument [Line Items]
Aggregate principal amount				$ 90,000,000
Interest rate (as a percent)				3.77%
Minimum
Debt Instrument [Line Items]
Interest and dividend coverage ratio			1.50
Minimum | OTC Credit Agreement | Prime Rate, Federal Funds Rate or LIBOR
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate (as a percent)			2.00%
Minimum | OTC Credit Agreement | Benchmark Rate
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate (as a percent)			0.00%
Maximum
Debt Instrument [Line Items]
Debt to total capitalization ratio			60.00%
Maximum | OTC Credit Agreement | Prime Rate, Federal Funds Rate or LIBOR
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate (as a percent)			0.125%
Maximum | OTC Credit Agreement | Benchmark Rate
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate (as a percent)			1.75%

Pension Plan and Other Postre_3

Pension Plan and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost–Benefit Earned During the Period	$ 1,866	$ 1,655	$ 5,597	$ 4,966
Interest Cost on Projected Benefit Obligation	2,915	3,264	8,745	9,790
Expected Return on Assets	(5,590)	(5,506)	(16,769)	(16,516)
Amortization of Net Actuarial Loss:
From Regulatory Asset	2,660	2,231	7,981	6,693
From Other Comprehensive Income	68	55	204	165
Net Periodic Pension Cost	1,919	1,699	5,758	5,098
Executive Survivor and Supplemental Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost–Benefit Earned During the Period	47	45	140	134
Interest Cost on Projected Benefit Obligation	307	362	921	1,086
Amortization of Net Actuarial Loss:
From Regulatory Asset	30	24	92	71
From Other Comprehensive Income	124	85	373	256
Net Periodic Pension Cost	508	516	1,526	1,547
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost–Benefit Earned During the Period	430	461	1,291	1,385
Interest Cost on Projected Benefit Obligation	472	598	1,418	1,795
Amortization of Prior Service Cost:
From Regulatory Asset	(1,397)	(1,169)	(4,192)	(3,508)
From Other Comprehensive Income	(35)	(28)	(107)	(86)
Amortization of Net Actuarial Loss:
From Regulatory Asset	919	1,051	2,759	3,154
From Other Comprehensive Income	24	26	71	78
Net Periodic Pension Cost	$ 413	$ 939	$ 1,240	$ 2,818

Pension Plan and Other Postre_4

Pension Plan and Other Postretirement Benefits - Narrative (Details) $ in Millions	1 Months Ended
	Jan. 31, 2021USD ($)
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer	$ 10

Income Taxes - Effective Income

Income Taxes - Effective Income Tax Rate (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Federal Statutory Rate	21.00%	21.00%	21.00%	21.00%
Increases (Decreases) in Tax from:
State Taxes on Income, Net of Federal Tax	5.00%	5.00%	5.00%	5.00%
Production Tax Credits (PTCs)	(5.00%)	0.00%	(6.00%)	0.00%
Amortization of Excess Deferred Income Taxes	(1.60%)	(2.90%)	(2.00%)	(3.40%)
North Dakota Wind Tax Credit Amortization, Net of Federal Tax	(0.20%)	(0.60%)	(0.30%)	(0.80%)
Excess Tax Deduction on Stock Awards	0.00%	0.30%	0.00%	(0.40%)
Allowance for Equity Funds Used During Construction	(0.10%)	(0.70%)	(0.10%)	(0.80%)
Other, Net	(0.80%)	(1.90%)	(0.70%)	(1.20%)
Effective Tax Rate	18.30%	20.20%	16.90%	19.40%

Commitments and Contingencies (

Commitments and Contingencies (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)
Pending Litigation | Westmoreland Arbitration
Other Commitments [Line Items]
Recovery sought	$ 5.5
Otter Tail Power Company | Coyote Station
Other Commitments [Line Items]
Ownership percentage	35.00%
Otter Tail Power Company | Federal Energy Regulatory Commission
Other Commitments [Line Items]
Estimated liability of refund obligation	$ 3

Stockholders' Equity (Details)

Stockholders' Equity (Details) - USD ($) $ in Thousands	May 03, 2021	Jul. 15, 2020	Sep. 30, 2021	Dec. 31, 2020
Class of Stock [Line Items]
Total capitalization			$ 1,547,101	$ 1,495,398
Otter Tail Power Company
Class of Stock [Line Items]
Equity to total capitalization ratio			52.60%
Net assets restricted from distribution			$ 674,900
Minimum | Otter Tail Power Company | Minnesota Public Utilities Commission
Class of Stock [Line Items]
Public utilities, requested equity capital structure, percentage		47.50%
Maximum | Otter Tail Power Company
Class of Stock [Line Items]
Total capitalization			$ 1,700,000
Maximum | Otter Tail Power Company | Minnesota Public Utilities Commission
Class of Stock [Line Items]
Public utilities, requested equity capital structure, percentage		58.10%
Second Shelf Registration
Class of Stock [Line Items]
Shelf registration (in shares)	1,500,000

Share-Based Payments - Narrativ

Share-Based Payments - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment arrangement, expense	$ 0.8	$ 1.3	$ 6.4	$ 5.3
Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards vesting period			4 years
Fair value of awards vested			$ 2.1	2.8
Stock Awards | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period			3 years
Stock Awards | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period			4 years
Stock Performance Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period			3 years
Fair value of awards vested			$ 2.5	$ 3.4
Stock Performance Awards | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of target amount as actual payment			0.00%
Stock Performance Awards | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of target amount as actual payment			150.00%

Share-Based Payments - Summary

Share-Based Payments - Summary of Restricted Stock Awards and Stock Performance Awards (Details)	9 Months Ended
	Sep. 30, 2021$ / sharesshares
Stock Awards
Shares
Beginning of year (in shares) | shares	128,664
Granted (in shares) | shares	57,650
Vested (in shares) | shares	(47,646)
Forfeited (in shares) | shares	(2,075)
End of year (in shares) | shares	136,593
Weighted Average Grant-Date Fair Value
Beginning of year (in dollars per share) | $ / shares	$ 44.30
Granted (in dollars per share) | $ / shares	43.10
Vested (in dollars per share) | $ / shares	42.98
Forfeited (in dollars per share) | $ / shares	40.95
End of year (in dollars per share) | $ / shares	$ 44.30
Stock Performance Awards
Shares
Beginning of year (in shares) | shares	164,600
Granted (in shares) | shares	79,000
Vested (in shares) | shares	(54,000)
Forfeited (in shares) | shares	0
End of year (in shares) | shares	189,600
Weighted Average Grant-Date Fair Value
Beginning of year (in dollars per share) | $ / shares	$ 42.32
Granted (in dollars per share) | $ / shares	38.34
Vested (in dollars per share) | $ / shares	35.73
Forfeited (in dollars per share) | $ / shares	0
End of year (in dollars per share) | $ / shares	$ 42.54

Share-Based Payments - Weighted

Share-Based Payments - Weighted-Average Assumptions (Details) - Stock Performance Awards	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	0.18%	1.42%
Expected term (in years)	3 years	3 years
Expected volatility	32.00%	19.00%
Dividend yield	3.60%	2.80%

Earnings Per Share (Details)

Earnings Per Share (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Weighted Average Common Shares Outstanding - Basic (in shares)	41,504	40,914	41,487	40,548
Effect of Dilutive Securities:
Total Dilutive Shares (in shares)	365	164	308	185
Weighted Average Common Shares Outstanding – Diluted (in shares)	41,869	41,078	41,795	40,733
Stock Performance Awards
Effect of Dilutive Securities:
Effect of Dilutive Securities (in shares)	262	98	209	107
Stock Awards
Effect of Dilutive Securities:
Effect of Dilutive Securities (in shares)	88	49	82	53
Employee Stock Purchase Plan Shares and Other
Effect of Dilutive Securities:
Effect of Dilutive Securities (in shares)	15	17	17	25

Derivative Instruments (Details

Derivative Instruments (Details) $ in Millions	Sep. 30, 2021USD ($)MWh
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair value of outstanding swap agreements	$ 6.9
Other Current Assets
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair value of outstanding swap agreements	6.1
Other Noncurrent Assets
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair value of outstanding swap agreements	$ 0.8
Swap
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount of outstanding swap agreements | MWh	356,200

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Fair Value Measurements, Recurring and Nonrecurring (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities	$ 9,208	$ 9,260
Derivative Instruments	6,900
Level 1 | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money Market Funds	953	4,075
Mutual Funds	5,170	1,662
Total Assets	6,123	5,737
Level 2 | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Instruments	6,923
Total Assets	16,131	9,260
Level 2 | Fair Value, Recurring | Corporate Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities	2,377	2,627
Level 2 | Fair Value, Recurring | Government-Backed and Government-Sponsored Enterprises’ Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities	$ 6,831	$ 6,633

Fair Value Measurements - Sch_2

Fair Value Measurements - Schedule of Fair Value of Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Carrying Amount
Assets:
Cash and Cash Equivalents	$ 1,272	$ 1,163
Total Assets	1,272	1,163
Liabilities:
Short-Term Debt	97,857	80,997
Long-Term Debt	764,581	764,519
Total	862,438	845,516
Fair Value
Assets:
Cash and Cash Equivalents	1,272	1,163
Total Assets	1,272	1,163
Liabilities:
Short-Term Debt	97,857	80,997
Long-Term Debt	873,632	858,455
Total	$ 971,489	$ 939,452