Otter Tail (OTTR) 10-Q 6 Aug 21 2021 Q2 Quarterly report Financial data

Cover

Cover - shares	6 Months Ended
	Jun. 30, 2021	Jul. 30, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 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		41,539,334
Entity Central Index Key	0001466593
Amendment Flag	false
Document Fiscal Period Focus	Q2
Document Fiscal Year Focus	2021
Current Fiscal Year End Date	--12-31

Consolidated Balance Sheets (un

Consolidated Balance Sheets (unaudited) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Current Assets
Cash and Cash Equivalents	$ 1,480	$ 1,163
Receivables, net of allowance for credit losses	163,424	113,959
Inventories	103,024	92,165
Regulatory Assets	23,250	21,900
Other Current Assets	13,723	5,645
Total Current Assets	304,901	234,832
Noncurrent Assets
Investments	55,809	51,856
Property, Plant and Equipment, net of accumulated depreciation	2,073,009	2,049,273
Regulatory Assets	160,018	168,395
Intangible Assets, net of accumulated amortization	9,594	10,144
Goodwill	37,572	37,572
Other Noncurrent Assets	30,684	26,282
Total Noncurrent Assets	2,366,686	2,343,522
Total Assets	2,671,587	2,578,354
Current Liabilities
Short-Term Debt	127,957	80,997
Current Maturities of Long-Term Debt	139,963	140,087
Accounts Payable	131,214	130,805
Accrued Salaries and Wages	23,775	26,908
Accrued Taxes	14,531	18,831
Regulatory Liabilities	17,301	16,663
Other Current Liabilities	28,743	22,495
Total Current Liabilities	483,484	436,786
Noncurrent Liabilities and Deferred Credits
Pensions Benefit Liability	102,331	114,055
Other Postretirement Benefits Liability	67,538	67,359
Regulatory Liabilities	231,766	233,973
Deferred Income Taxes	167,612	153,376
Deferred Tax Credits	17,033	17,405
Other Noncurrent Liabilities	62,160	60,002
Total Noncurrent Liabilities and Deferred Credits	648,440	646,170
Commitments and Contingencies (Note 9)
Capitalization
Long-Term Debt, net of current maturities	624,540	624,432
Shareholders' Equity
Common Shares: 50,000,000 shares authorized of $5 par value; 41,538,709 and 41,469,879 outstanding at June 30, 2021 and December 31, 2020	207,694	207,349
Additional Paid-In Capital	417,870	414,246
Retained Earnings	297,850	257,878
Accumulated Other Comprehensive Loss	(8,291)	(8,507)
Total Shareholders' Equity	915,123	870,966
Total Capitalization	1,539,663	1,495,398
Total Liabilities and Shareholders' Equity	$ 2,671,587	$ 2,578,354

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parentheticals) - $ / shares	Jun. 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)	41,538,709	41,469,879

Consolidated Statements of Inco

Consolidated Statements of Income (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Operating Revenues
Total Operating Revenues	$ 285,608	$ 192,756	$ 547,318	$ 427,503
Operating Expenses
Electric Production Fuel	12,164	8,788	26,878	22,523
Electric Purchased Power	11,135	13,682	30,395	32,512
Electric Operating and Maintenance Expenses	36,729	33,179	78,150	73,794
Cost of Products Sold (excluding depreciation)	122,578	73,832	224,555	159,711
Other Nonelectric Expenses	15,669	10,762	29,362	22,662
Depreciation and Amortization	23,169	20,436	45,295	40,835
Electric Property Taxes	4,342	4,168	8,662	8,268
Total Operating Expenses	225,786	164,847	443,297	360,305
Operating Income	59,822	27,909	104,021	67,198
Other Income and Expense
Interest Charges	9,555	8,662	18,953	16,785
Nonservice Cost Components of Postretirement Benefits	624	868	1,006	1,739
Other Income (Expense), net	734	2,410	1,892	2,021
Income Before Income Taxes	50,377	20,789	85,954	50,695
Income Tax Expense	8,308	3,808	13,556	9,446
Net Income	$ 42,069	$ 16,981	$ 72,398	$ 41,249
Weighted-Average Common Shares Outstanding:
Basic (in shares)	41,500	40,513	41,478	40,365
Diluted (in shares)	41,818	40,677	41,759	40,561
Earnings Per Share:
Basic (in dollars per share)	$ 1.01	$ 0.42	$ 1.75	$ 1.02
Diluted (in dollars per share)	$ 1.01	$ 0.42	$ 1.73	$ 1.02
Electric
Operating Revenues
Total Operating Revenues	$ 106,155	$ 98,130	$ 229,855	$ 218,000
Product Sales
Operating Revenues
Total Operating Revenues	$ 179,453	$ 94,626	$ 317,463	$ 209,503

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement of Comprehensive Income [Abstract]
Net Income	$ 42,069	$ 16,981	$ 72,398	$ 41,249
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)	(38)	32	(43)	34
Unrealized Gains (Losses)	(11)	92	(52)	218
Income Tax (Expense) Benefit	10	(26)	20	(53)
Available-for-Sale Securities, net of tax	(39)	98	(75)	199
Pension and Postretirement Benefit Plans:
Amortization of Unrecognized Postretirement Benefit Losses and Costs	190	137	394	275
Income Tax Expense	(50)	(36)	(103)	(72)
Pension and Postretirement Benefit Plan, net of tax	140	101	291	203
Total Other Comprehensive Income	101	199	216	402
Total Comprehensive Income	$ 42,170	$ 17,180	$ 72,614	$ 41,651

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)		729,454
Common Stock Issuances, Net of Expenses	26,869	$ 3,647	23,222
Common Stock Retirements and Forfeitures (in shares)		(38,217)
Common Stock Retirements and Forfeitures	(2,069)	$ (191)	(1,878)
Net Income	41,249			41,249
Other Comprehensive Income	402				402	[1]
Stock Compensation Expense	4,007		4,007
Common Dividends	(29,885)			(29,885)
Ending balance, shares (in shares) at Jun. 30, 2020		40,848,828
Ending balance at Jun. 30, 2020	822,055	$ 204,244	390,141	233,705	(6,035)	[1]
Beginning balance, shares (in shares) at Mar. 31, 2020		40,376,448
Beginning balance at Mar. 31, 2020	800,019	$ 201,882	372,669	231,702	(6,234)	[1]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock Issuances, Net of Expenses (in shares)		472,380
Common Stock Issuances, Net of Expenses	18,597	$ 2,362	16,235
Net Income	16,981			16,981
Other Comprehensive Income	199				199	[1]
Stock Compensation Expense	1,237		1,237
Common Dividends	(14,978)			(14,978)
Ending balance, shares (in shares) at Jun. 30, 2020		40,848,828
Ending balance at Jun. 30, 2020	822,055	$ 204,244	390,141	233,705	(6,035)	[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)		104,531
Common Stock Issuances, Net of Expenses	(48)	$ 524	(572)
Common Stock Retirements and Forfeitures (in shares)		(35,701)
Common Stock Retirements and Forfeitures	(1,507)	$ (179)	(1,328)
Net Income	72,398			72,398
Other Comprehensive Income	216				216	[1]
Stock Compensation Expense	5,524		5,524
Common Dividends	(32,426)			(32,426)
Ending balance, shares (in shares) at Jun. 30, 2021		41,538,709
Ending balance at Jun. 30, 2021	915,123	$ 207,694	417,870	297,850	(8,291)	[1]	134	(8,425)
Beginning balance, shares (in shares) at Mar. 31, 2021		41,510,455
Beginning balance at Mar. 31, 2021	887,866	$ 207,552	416,707	271,999	(8,392)	[1]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock Issuances, Net of Expenses (in shares)		28,254
Common Stock Issuances, Net of Expenses	(22)	$ 142	(164)
Net Income	42,069			42,069
Other Comprehensive Income	101				101	[1]
Stock Compensation Expense	1,327		1,327
Common Dividends	(16,218)			(16,218)
Ending balance, shares (in shares) at Jun. 30, 2021		41,538,709
Ending balance at Jun. 30, 2021	$ 915,123	$ 207,694	$ 417,870	$ 297,850	(8,291)	[1]	134	(8,425)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Before Tax					(11,229)		170	(11,399)
Tax Effect					$ 2,938		$ (36)	$ 2,974
[1]	1 Accumulated Other Comprehensive Income (Loss) as of June 30, 2021 and December 31, 2020 is comprised of the following: (in thousands) June 30, December 31, Unrealized Gain on Available-for-Sale Debt Securities: Before Tax $ 170 $ 265 Tax Effect (36) (56) Unrealized Gain on Available-for-Sale Debt, net of tax 134 209 Unamortized Actuarial Losses and Prior Service Costs Related to Pension and Postretirement Benefits: Before Tax (11,399) (11,793) Tax Effect 2,974 3,077 Unamortized Actuarial Losses and Prior Service Costs Related to Pension and Postretirement Benefits, net of tax (8,425) (8,716) Accumulated Other Comprehensive Loss: Before Tax (11,229) (11,528) Tax Effect 2,938 3,021 Net Accumulated Other Comprehensive Loss $ (8,291) $ (8,507)

Consolidated Statements of Sh_2

Consolidated Statements of Shareholders' Equity (Parentheticals) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement of Stockholders' Equity [Abstract]
Common Dividends (in dollars per share)	$ 0.39	$ 0.37	$ 0.78	$ 0.74

Consolidated Statements of Cash

Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Operating Activities
Net Income	$ 72,398	$ 41,249
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:
Depreciation and Amortization	45,295	40,835
Deferred Tax Credits	(372)	(657)
Deferred Income Taxes	11,327	9,472
Change in Deferred Debits and Other Assets	5,749	5,565
Discretionary Contribution to Pension Plan	(10,000)	(11,200)
Change in Noncurrent Liabilities and Deferred Credits	(3,710)	5,178
Allowance for Equity Funds Used During Construction	(172)	(1,858)
Stock Compensation Expense	5,524	4,007
Other, Net	(3,246)	(147)
Cash (Used for) Provided by Current Assets and Current Liabilities:
Change in Receivables	(49,465)	(3,929)
Change in Inventories	(10,859)	8,097
Change in Other Current Assets	(8,080)	(1,066)
Change in Payables and Other Current Liabilities	12,375	(23,562)
Change in Interest Payable and Income Taxes Receivable/Payable	1,810	1,917
Net Cash Provided by Operating Activities	68,574	73,901
Investing Activities
Capital Expenditures	(76,891)	(119,830)
Proceeds from Disposal of Noncurrent Assets	4,562	3,953
Cash Used for Investments and Other Assets	(4,074)	(5,128)
Net Cash Used in Investing Activities	(76,403)	(121,005)
Financing Activities
Change in Checks Written in Excess of Cash	(4,586)	550
Net Short-Term Borrowings	46,960	35,239
Proceeds from Issuance of Common Stock	0	27,225
Common Stock Issuance Expenses	(67)	(374)
Payments for Shares Withheld for Employee Tax Obligations	(1,507)	(2,069)
Proceeds from Issuance of Long-Term Debt	0	35,000
Debt Issuance Expenses	(59)	(179)
Payments for Retirement of Long-Term Debt	(169)	(90)
Dividends Paid	(32,426)	(29,885)
Net Cash Provided by Financing Activities	8,146	65,417
Net Change in Cash and Cash Equivalents	317	18,313
Cash and Cash Equivalents at Beginning of Period	1,163	21,199
Cash and Cash Equivalents at End of Period	1,480	39,512
Supplemental Disclosure of Noncash Investing Activities
Transactions Related to Capital Additions Not Settled in Cash	$ 9,875	$ 61,925

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 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 six months ended June 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	6 Months Ended
	Jun. 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 six months ended June 30, 2021 and 2020 are as follows: Three Months Ended June 30, Six Months Ended June 30, (in thousands) 2021 2020 2021 2020 Operating Revenue 1 Electric $ 106,155 $ 98,130 $ 229,855 $ 218,000 Manufacturing 84,284 45,947 160,107 114,427 Plastics 95,169 48,679 157,356 95,076 Total $ 285,608 $ 192,756 $ 547,318 $ 427,503 Net Income (Loss) Electric $ 15,433 $ 13,306 $ 33,019 $ 29,488 Manufacturing 5,705 238 11,089 5,165 Plastics 22,544 5,130 31,692 10,579 Corporate (1,613) (1,693) (3,402) (3,983) Total $ 42,069 $ 16,981 $ 72,398 $ 41,249 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 June 30, 2021 and December 31, 2020: (in thousands) June 30, December 31, Identifiable Assets Electric $ 2,259,896 $ 2,233,399 Manufacturing 220,896 191,005 Plastics 136,604 99,767 Corporate 54,191 54,183 Total $ 2,671,587 $ 2,578,354

Revenue

Revenue	6 Months Ended
	Jun. 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 six months ended June 30, 2021 and 2020: Three Months Ended June 30, Six Months Ended June 30, (in thousands) 2021 2020 2021 2020 Operating Revenues Electric Segment Retail: Residential $ 28,709 $ 27,862 $ 66,176 $ 63,705 Retail: Commercial and Industrial 58,390 55,914 124,811 124,853 Retail: Other 1,888 1,777 3,706 3,598 Total Retail 88,987 85,553 194,693 192,156 Transmission 11,840 9,673 23,785 20,514 Wholesale 3,260 765 7,767 1,641 Other 2,068 2,139 3,610 3,689 Total Electric Segment 106,155 98,130 229,855 218,000 Manufacturing Segment Metal Parts and Tooling 71,013 37,266 133,686 94,478 Plastic Products and Tooling 10,131 7,840 20,426 17,723 Scrap Metal Sales 3,140 841 5,995 2,226 Total Manufacturing Segment 84,284 45,947 160,107 114,427 Plastics Segment PVC Pipe 95,169 48,679 157,356 95,076 Total Operating Revenue 285,608 192,756 547,318 427,503 Less: Noncontract Revenues Included Above Electric Segment - ARP Revenues (1,782) 209 (2,757) 122 Total Operating Revenues from Contracts with Customers $ 287,390 $ 192,547 $ 550,075 $ 427,381

Select Balance Sheet Informatio

Select Balance Sheet Information	6 Months Ended
	Jun. 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 June 30, 2021 and December 31, 2020 are as follows: (in thousands) June 30, December 31, Receivables Trade $ 135,744 $ 87,048 Other 12,252 8,939 Unbilled Receivables 18,154 21,187 Total Receivables 166,150 117,174 Less: Allowance for Credit Losses 2,726 3,215 Receivables, net of allowance for credit losses $ 163,424 $ 113,959 The following is a summary of activity in the allowance for credit losses for the six months ended June 30, 2021 and 2020: (in thousands) 2021 2020 Beginning Balance, January 1 $ 3,215 $ 1,339 Additions Charged to Expense 284 1,371 Reductions for Amounts Written-Off, Net of Recoveries (773) (655) Ending Balance, June 30 $ 2,726 $ 2,055 Inventories Inventories consist of the following as of June 30, 2021 and December 31, 2020: (in thousands) June 30, December 31, Finished Goods $ 21,272 $ 22,046 Work in Process 24,140 16,210 Raw Material, Fuel and Supplies 57,612 53,909 Total Inventories $ 103,024 $ 92,165 Investments The following is a summary of our investments as of June 30, 2021 and December 31, 2020: (in thousands) June 30, December 31, Corporate-Owned Life Insurance Policies $ 39,492 $ 36,825 Debt Securities 9,227 9,260 Money Market Funds 1,861 4,075 Mutual Funds 5,201 1,662 Other Investments 28 34 Total Investments $ 55,809 $ 51,856 The amount of unrealized gains and losses on debt securities as of June 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 June 30, 2021 and December 31, 2020 are not material. Property, Plant and Equipment Major classes of property, plant and equipment as of June 30, 2021 and December 31, 2020 include: (in thousands) June 30, December 31, Electric Plant in Service Electric Plant in Service $ 2,699,352 $ 2,531,352 Construction Work in Progress 87,676 203,078 Total Gross Electric Plant 2,787,028 2,734,430 Less Accumulated Depreciation and Amortization 811,134 778,988 Net Electric Plant 1,975,894 1,955,442 Nonelectric Property, Plant and Equipment Nonelectric Property, Plant and Equipment in Service 261,065 258,730 Construction Work in Progress 12,936 9,290 Total Gross Nonelectric Property, Plant and Equipment 274,001 268,020 Less Accumulated Depreciation and Amortization 176,886 174,189 Net Nonelectric Property, Plant and Equipment 97,115 93,831 Net Property, Plant and Equipment $ 2,073,009 $ 2,049,273

Regulatory Matters

Regulatory Matters	6 Months Ended
	Jun. 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 June 30, 2021 and December 31, 2020 and the period we expect to recover or refund such amounts: Period of June 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 $ 141,668 $ 11,037 $ 146,071 Alternative Revenue Program Riders 2 Up to 3 years 6,505 8,982 8,871 9,373 Asset Retirement Obligations 1 Asset lives — 6,696 — 8,462 ISO Cost Recovery Trackers 1 Up to 2 years 539 724 1,079 867 Unrecovered Project Costs 1 Up to 3 years 4,114 1,492 361 2,989 Deferred Rate Case Expenses 1 Various 888 110 360 230 Debt Reacquisition Premiums 1 Up to 12 years 167 263 192 341 Other 1 Various — 83 — 62 Total Regulatory Assets $ 23,250 $ 160,018 $ 21,900 $ 168,395 Regulatory Liabilities Deferred Income Taxes Asset lives $ — $ 131,893 $ — $ 134,719 Plant Removal Obligations Asset lives 5,556 96,164 — 98,707 Fuel Clause Adjustments Up to 1 year 6,531 — 10,947 — Alternative Revenue Program Riders Various 3,094 1,761 3,581 470 Pension and Other Postretirement Benefit Plans Up to 1 year 1,959 — 1,959 — Other Various 161 1,948 176 77 Total Regulatory Liabilities $ 17,301 $ 231,766 $ 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	6 Months Ended
	Jun. 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 June 30, 2021 and December 31, 2020: Short-Term Debt The following is a summary of our lines of credit as of June 30, 2021 and December 31, 2020: June 30, 2021 December 31, (in thousands) Line Limit Amount Outstanding Letters Amount Available Amount Available OTC Credit Agreement $ 170,000 $ 59,245 $ — $ 110,755 $ 104,834 OTP Credit Agreement 170,000 68,712 12,671 88,617 140,068 Total $ 340,000 $ 127,957 $ 12,671 $ 199,372 $ 244,902 Both credit agreements are in place until October 31, 2024. Long-Term Debt The following is a summary of outstanding long-term debt by borrower as of June 30, 2021 and December 31, 2020: (in thousands) Entity Debt Instrument Rate Maturity June 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 139,963 140,087 Unamortized Long-Term Debt Issuance Costs 2,497 2,650 Total Long-Term Debt Net of Unamortized Debt Issuance Costs $ 624,540 $ 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 in aggregate principal amount of its 2.74% Series 2021A Senior Unsecured Notes due November 29, 2031, (b) $100 million in aggregate principal amount of its 3.69% Series 2021B Senior Unsecured Notes due November 29, 2051 and (c) $90 million in aggregate principal amount of its 3.77% Series 2022A Senior Unsecured Notes due May 20, 2052. As of June 30, 2021, there were no amounts outstanding. The funding of the notes will occur in two issuances, $140.0 million in November 2021 and $90.0 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 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 June 30, 2021, OTC and OTP were in compliance with these financial covenants.

Pension Plan and Other Postreti

Pension Plan and Other Postretirement Benefits	6 Months Ended
	Jun. 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 six months ended June 30, 2021 and 2020 are as follows: Three Months Ended June 30, Six Months Ended June 30, (in thousands) 2021 2020 2021 2020 Service Cost–Benefit Earned During the Period $ 1,865 $ 1,656 $ 3,731 $ 3,311 Interest Cost on Projected Benefit Obligation 2,915 3,263 5,830 6,526 Expected Return on Assets (5,589) (5,505) (11,179) (11,010) Amortization of Net Actuarial Loss: From Regulatory Asset 2,661 2,231 5,321 4,462 From Other Comprehensive Income 68 55 136 110 Net Periodic Pension Cost $ 1,920 $ 1,700 $ 3,839 $ 3,399 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 six months ended June 30, 2021 and 2020 are as follows: Three Months Ended June 30, Six Months Ended June 30, (in thousands) 2021 2020 2021 2020 Service Cost–Benefit Earned During the Period $ 46 $ 44 $ 93 $ 89 Interest Cost on Projected Benefit Obligation 307 362 614 724 Amortization of Net Actuarial Loss: From Regulatory Asset 31 24 62 47 From Other Comprehensive Income 125 85 249 171 Net Periodic Pension Cost $ 509 $ 515 $ 1,018 $ 1,031 Other Postretirement Benefits Components of net periodic postretirement benefit cost for the three and six months ended June 30, 2021 and 2020 are as follows: Three Months Ended June 30, Six Months Ended June 30, (in thousands) 2021 2020 2021 2020 Service Cost–Benefit Earned During the Period $ 431 $ 462 $ 861 $ 924 Interest Cost on Projected Benefit Obligation 473 599 946 1,197 Amortization of Prior Service Cost From Regulatory Asset (1,398) (1,170) (2,795) (2,339) From Other Comprehensive Income (36) (29) (72) (58) Amortization of Net Actuarial Loss From Regulatory Asset 920 1,052 1,840 2,103 From Other Comprehensive Income 24 26 47 52 Net Periodic Postretirement Benefit Cost $ 414 $ 940 $ 827 $ 1,879

Income Taxes

Income Taxes	6 Months Ended
	Jun. 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 six months ended June 30, 2021 and 2020 is as follows: Three Months Ended June 30, Six Months Ended June 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) (6.3) — (6.8) — Amortization of Excess Deferred Income Taxes (2.0) (3.4) (2.4) (3.8) North Dakota Wind Tax Credit Amortization, Net of Federal Tax (0.3) (1.2) (0.3) (1.0) Excess Tax Deduction on Stock Awards — (0.6) — (1.0) Allowance for Equity Funds Used During Construction (0.1) (0.8) (0.1) (1.0) Other, Net (0.8) (1.7) (0.6) (0.6) Effective Tax Rate 16.5 % 18.3 % 15.8 % 18.6 % We began generating PTCs from our Merricourt wind farm placed in service in the fourth quarter of 2020. No PTCs were generated during the six months ended June 30, 2020. Income tax benefits arising from PTCs are offset by corresponding operating revenue reductions.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 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. T.O. Plastics is party to a resin supply agreement under which it must purchase all of a specified class of regrind resin delivered by the supplier at a periodically negotiated price per pound. The agreement expires in 2026. 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 $3.5 million as of June 30, 2021. This refund liability reflects our best estimate of required refunds to customers once all regulatory and judicial proceedings are finalized. 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, with state implementation plans targeted for submission to the EPA by July 31, 2021. States are required 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. We cannot predict with certainty the impact the state implementation plan may have on our business until the plan is finalized and adopted. 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 a required early retirement of, or the sale of our interest in, Coyote Station. 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. The arbitration was delayed through an effort to seek dispensation of the matter through the courts and through dispositive motions. The arbitration hearing is anticipated to be held in late 2021. 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 June 30, 2021, other than those discussed above, will not be material.

Stockholders' Equity

Stockholders' Equity	6 Months Ended
	Jun. 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 June 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	6 Months Ended
	Jun. 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 $1.3 million and $1.2 million for the three months ended June 30, 2021 and 2020, respectively, and $5.5 million and $4.0 million for the six months ended June 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 six months ended June 30, 2021: Shares Weighted Average Nonvested, January 1, 2021 128,664 $ 44.30 Granted 57,650 43.10 Vested (46,371) 43.04 Forfeited (1,577) 40.77 Nonvested, June 30, 2021 138,366 $ 44.26 The fair value of vested awards was $2.1 million and $2.8 million during the six months ended June 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 six months ended June 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 six months ended June 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, June 30, 2021 189,600 $ 42.54

Earnings Per Share

Earnings Per Share	6 Months Ended
	Jun. 30, 2021
Earnings Per Share [Abstract]
Earnings Per Share	Earnings Per Share The 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 six months ended June 30, 2021 and 2020: Three Months Ended June 30, Six Months Ended June 30, (in thousands) 2021 2020 2021 2020 Weighted Average Common Shares Outstanding – Basic 41,500 40,513 41,478 40,365 Effect of Dilutive Securities: Stock Performance Awards 223 97 183 112 Stock Awards 75 47 80 56 Employee Stock Purchase Plan Shares and Other 20 20 18 28 Dilutive Effect of Potential Common Shares 318 164 281 196 Weighted Average Common Shares Outstanding – Diluted 41,818 40,677 41,759 40,561 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 six months ended June 30, 2021 and 2020.

Derivative Instruments

Derivative Instruments	6 Months Ended
	Jun. 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 June 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 June 30, 2021, the fair value of these contracts was $1.9 million, which is included in other current assets on the consolidated balance sheets.

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 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 June 30, 2021 and December 31, 2020 classified by the input method used to measure fair value: Level 1 Level 2 Level 3 June 30, 2021 Investments: Money Market Funds $ 1,861 $ — $ — Mutual Funds 5,201 — — Corporate Debt Securities — 2,393 — Government-Backed and Government-Sponsored Enterprises’ Debt Securities — 6,835 — Derivative Instruments — 1,879 — Total Assets $ 7,062 $ 11,107 $ — 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 June 30, 2021 and December 31, 2020: June 30, 2021 December 31, 2020 (in thousands) Carrying Fair Value Carrying Fair Value Cash and Cash Equivalents $ 1,480 $ 1,480 $ 1,163 $ 1,163 Short-Term Debt (127,957) (127,957) (80,997) (80,997) Long-Term Debt (764,503) (875,405) (764,519) (858,455) 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)	6 Months Ended
	Jun. 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 six months ended June 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)	6 Months Ended
	Jun. 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 six months ended June 30, 2021 and 2020 are as follows: Three Months Ended June 30, Six Months Ended June 30, (in thousands) 2021 2020 2021 2020 Operating Revenue 1 Electric $ 106,155 $ 98,130 $ 229,855 $ 218,000 Manufacturing 84,284 45,947 160,107 114,427 Plastics 95,169 48,679 157,356 95,076 Total $ 285,608 $ 192,756 $ 547,318 $ 427,503 Net Income (Loss) Electric $ 15,433 $ 13,306 $ 33,019 $ 29,488 Manufacturing 5,705 238 11,089 5,165 Plastics 22,544 5,130 31,692 10,579 Corporate (1,613) (1,693) (3,402) (3,983) Total $ 42,069 $ 16,981 $ 72,398 $ 41,249 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 June 30, 2021 and December 31, 2020: (in thousands) June 30, December 31, Identifiable Assets Electric $ 2,259,896 $ 2,233,399 Manufacturing 220,896 191,005 Plastics 136,604 99,767 Corporate 54,191 54,183 Total $ 2,671,587 $ 2,578,354

Revenue (Tables)

Revenue (Tables)	6 Months Ended
	Jun. 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 six months ended June 30, 2021 and 2020: Three Months Ended June 30, Six Months Ended June 30, (in thousands) 2021 2020 2021 2020 Operating Revenues Electric Segment Retail: Residential $ 28,709 $ 27,862 $ 66,176 $ 63,705 Retail: Commercial and Industrial 58,390 55,914 124,811 124,853 Retail: Other 1,888 1,777 3,706 3,598 Total Retail 88,987 85,553 194,693 192,156 Transmission 11,840 9,673 23,785 20,514 Wholesale 3,260 765 7,767 1,641 Other 2,068 2,139 3,610 3,689 Total Electric Segment 106,155 98,130 229,855 218,000 Manufacturing Segment Metal Parts and Tooling 71,013 37,266 133,686 94,478 Plastic Products and Tooling 10,131 7,840 20,426 17,723 Scrap Metal Sales 3,140 841 5,995 2,226 Total Manufacturing Segment 84,284 45,947 160,107 114,427 Plastics Segment PVC Pipe 95,169 48,679 157,356 95,076 Total Operating Revenue 285,608 192,756 547,318 427,503 Less: Noncontract Revenues Included Above Electric Segment - ARP Revenues (1,782) 209 (2,757) 122 Total Operating Revenues from Contracts with Customers $ 287,390 $ 192,547 $ 550,075 $ 427,381

Select Balance Sheet Informat_2

Select Balance Sheet Information (Tables)	6 Months Ended
	Jun. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Receivables	Receivables as of June 30, 2021 and December 31, 2020 are as follows: (in thousands) June 30, December 31, Receivables Trade $ 135,744 $ 87,048 Other 12,252 8,939 Unbilled Receivables 18,154 21,187 Total Receivables 166,150 117,174 Less: Allowance for Credit Losses 2,726 3,215 Receivables, net of allowance for credit losses $ 163,424 $ 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 six months ended June 30, 2021 and 2020: (in thousands) 2021 2020 Beginning Balance, January 1 $ 3,215 $ 1,339 Additions Charged to Expense 284 1,371 Reductions for Amounts Written-Off, Net of Recoveries (773) (655) Ending Balance, June 30 $ 2,726 $ 2,055
Schedule of Inventories	Inventories consist of the following as of June 30, 2021 and December 31, 2020: (in thousands) June 30, December 31, Finished Goods $ 21,272 $ 22,046 Work in Process 24,140 16,210 Raw Material, Fuel and Supplies 57,612 53,909 Total Inventories $ 103,024 $ 92,165
Schedule of Investments	The following is a summary of our investments as of June 30, 2021 and December 31, 2020: (in thousands) June 30, December 31, Corporate-Owned Life Insurance Policies $ 39,492 $ 36,825 Debt Securities 9,227 9,260 Money Market Funds 1,861 4,075 Mutual Funds 5,201 1,662 Other Investments 28 34 Total Investments $ 55,809 $ 51,856
Schedule of Property, Plant and Equipment	Major classes of property, plant and equipment as of June 30, 2021 and December 31, 2020 include: (in thousands) June 30, December 31, Electric Plant in Service Electric Plant in Service $ 2,699,352 $ 2,531,352 Construction Work in Progress 87,676 203,078 Total Gross Electric Plant 2,787,028 2,734,430 Less Accumulated Depreciation and Amortization 811,134 778,988 Net Electric Plant 1,975,894 1,955,442 Nonelectric Property, Plant and Equipment Nonelectric Property, Plant and Equipment in Service 261,065 258,730 Construction Work in Progress 12,936 9,290 Total Gross Nonelectric Property, Plant and Equipment 274,001 268,020 Less Accumulated Depreciation and Amortization 176,886 174,189 Net Nonelectric Property, Plant and Equipment 97,115 93,831 Net Property, Plant and Equipment $ 2,073,009 $ 2,049,273

Regulatory Matters (Tables)

Regulatory Matters (Tables)	6 Months Ended
	Jun. 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 June 30, 2021 and December 31, 2020 and the period we expect to recover or refund such amounts: Period of June 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 $ 141,668 $ 11,037 $ 146,071 Alternative Revenue Program Riders 2 Up to 3 years 6,505 8,982 8,871 9,373 Asset Retirement Obligations 1 Asset lives — 6,696 — 8,462 ISO Cost Recovery Trackers 1 Up to 2 years 539 724 1,079 867 Unrecovered Project Costs 1 Up to 3 years 4,114 1,492 361 2,989 Deferred Rate Case Expenses 1 Various 888 110 360 230 Debt Reacquisition Premiums 1 Up to 12 years 167 263 192 341 Other 1 Various — 83 — 62 Total Regulatory Assets $ 23,250 $ 160,018 $ 21,900 $ 168,395 Regulatory Liabilities Deferred Income Taxes Asset lives $ — $ 131,893 $ — $ 134,719 Plant Removal Obligations Asset lives 5,556 96,164 — 98,707 Fuel Clause Adjustments Up to 1 year 6,531 — 10,947 — Alternative Revenue Program Riders Various 3,094 1,761 3,581 470 Pension and Other Postretirement Benefit Plans Up to 1 year 1,959 — 1,959 — Other Various 161 1,948 176 77 Total Regulatory Liabilities $ 17,301 $ 231,766 $ 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)	6 Months Ended
	Jun. 30, 2021
Debt Disclosure [Abstract]
Schedule of Line of Credit Facilities	The following is a summary of our lines of credit as of June 30, 2021 and December 31, 2020: June 30, 2021 December 31, (in thousands) Line Limit Amount Outstanding Letters Amount Available Amount Available OTC Credit Agreement $ 170,000 $ 59,245 $ — $ 110,755 $ 104,834 OTP Credit Agreement 170,000 68,712 12,671 88,617 140,068 Total $ 340,000 $ 127,957 $ 12,671 $ 199,372 $ 244,902
Schedule of Debt	The following is a summary of outstanding long-term debt by borrower as of June 30, 2021 and December 31, 2020: (in thousands) Entity Debt Instrument Rate Maturity June 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 139,963 140,087 Unamortized Long-Term Debt Issuance Costs 2,497 2,650 Total Long-Term Debt Net of Unamortized Debt Issuance Costs $ 624,540 $ 624,432

Pension Plan and Other Postre_2

Pension Plan and Other Postretirement Benefits (Tables)	6 Months Ended
	Jun. 30, 2021
Retirement Benefits [Abstract]
Schedule of Net Benefit Costs	Components of net periodic pension benefit cost for the three and six months ended June 30, 2021 and 2020 are as follows: Three Months Ended June 30, Six Months Ended June 30, (in thousands) 2021 2020 2021 2020 Service Cost–Benefit Earned During the Period $ 1,865 $ 1,656 $ 3,731 $ 3,311 Interest Cost on Projected Benefit Obligation 2,915 3,263 5,830 6,526 Expected Return on Assets (5,589) (5,505) (11,179) (11,010) Amortization of Net Actuarial Loss: From Regulatory Asset 2,661 2,231 5,321 4,462 From Other Comprehensive Income 68 55 136 110 Net Periodic Pension Cost $ 1,920 $ 1,700 $ 3,839 $ 3,399 Components of net periodic pension benefit cost for the three and six months ended June 30, 2021 and 2020 are as follows: Three Months Ended June 30, Six Months Ended June 30, (in thousands) 2021 2020 2021 2020 Service Cost–Benefit Earned During the Period $ 46 $ 44 $ 93 $ 89 Interest Cost on Projected Benefit Obligation 307 362 614 724 Amortization of Net Actuarial Loss: From Regulatory Asset 31 24 62 47 From Other Comprehensive Income 125 85 249 171 Net Periodic Pension Cost $ 509 $ 515 $ 1,018 $ 1,031 Components of net periodic postretirement benefit cost for the three and six months ended June 30, 2021 and 2020 are as follows: Three Months Ended June 30, Six Months Ended June 30, (in thousands) 2021 2020 2021 2020 Service Cost–Benefit Earned During the Period $ 431 $ 462 $ 861 $ 924 Interest Cost on Projected Benefit Obligation 473 599 946 1,197 Amortization of Prior Service Cost From Regulatory Asset (1,398) (1,170) (2,795) (2,339) From Other Comprehensive Income (36) (29) (72) (58) Amortization of Net Actuarial Loss From Regulatory Asset 920 1,052 1,840 2,103 From Other Comprehensive Income 24 26 47 52 Net Periodic Postretirement Benefit Cost $ 414 $ 940 $ 827 $ 1,879

Income Taxes (Tables)

Income Taxes (Tables)	6 Months Ended
	Jun. 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 six months ended June 30, 2021 and 2020 is as follows: Three Months Ended June 30, Six Months Ended June 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) (6.3) — (6.8) — Amortization of Excess Deferred Income Taxes (2.0) (3.4) (2.4) (3.8) North Dakota Wind Tax Credit Amortization, Net of Federal Tax (0.3) (1.2) (0.3) (1.0) Excess Tax Deduction on Stock Awards — (0.6) — (1.0) Allowance for Equity Funds Used During Construction (0.1) (0.8) (0.1) (1.0) Other, Net (0.8) (1.7) (0.6) (0.6) Effective Tax Rate 16.5 % 18.3 % 15.8 % 18.6 %

Share-Based Payments (Tables)

Share-Based Payments (Tables)	6 Months Ended
	Jun. 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 six months ended June 30, 2021: Shares Weighted Average Nonvested, January 1, 2021 128,664 $ 44.30 Granted 57,650 43.10 Vested (46,371) 43.04 Forfeited (1,577) 40.77 Nonvested, June 30, 2021 138,366 $ 44.26
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 six months ended June 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, June 30, 2021 189,600 $ 42.54
Schedule of Weighted-Average Assumptions	The grant date fair value of stock performance awards granted during the six months ended June 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)	6 Months Ended
	Jun. 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 six months ended June 30, 2021 and 2020: Three Months Ended June 30, Six Months Ended June 30, (in thousands) 2021 2020 2021 2020 Weighted Average Common Shares Outstanding – Basic 41,500 40,513 41,478 40,365 Effect of Dilutive Securities: Stock Performance Awards 223 97 183 112 Stock Awards 75 47 80 56 Employee Stock Purchase Plan Shares and Other 20 20 18 28 Dilutive Effect of Potential Common Shares 318 164 281 196 Weighted Average Common Shares Outstanding – Diluted 41,818 40,677 41,759 40,561

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 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 June 30, 2021 and December 31, 2020 classified by the input method used to measure fair value: Level 1 Level 2 Level 3 June 30, 2021 Investments: Money Market Funds $ 1,861 $ — $ — Mutual Funds 5,201 — — Corporate Debt Securities — 2,393 — Government-Backed and Government-Sponsored Enterprises’ Debt Securities — 6,835 — Derivative Instruments — 1,879 — Total Assets $ 7,062 $ 11,107 $ — 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 June 30, 2021 and December 31, 2020: June 30, 2021 December 31, 2020 (in thousands) Carrying Fair Value Carrying Fair Value Cash and Cash Equivalents $ 1,480 $ 1,480 $ 1,163 $ 1,163 Short-Term Debt (127,957) (127,957) (80,997) (80,997) Long-Term Debt (764,503) (875,405) (764,519) (858,455)

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Details)	6 Months Ended
	Jun. 30, 2021segment
Accounting Policies [Abstract]
Number of operating segments	3

Segment Information - Narrative

Segment Information - Narrative (Details)	6 Months Ended
	Jun. 30, 2021segment
Segment Reporting [Abstract]
Number of reportable segments	3

Segment Information - Business

Segment Information - Business Segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Total Operating Revenues	$ 285,608	$ 192,756	$ 547,318	$ 427,503
Net Income (Loss)	42,069	16,981	72,398	41,249
Identifiable Assets	2,671,587		2,671,587		$ 2,578,354
Corporate
Segment Reporting Information [Line Items]
Net Income (Loss)	(1,613)	(1,693)	(3,402)	(3,983)
Identifiable Assets	54,191		54,191		54,183
Electric | Operating Segments
Segment Reporting Information [Line Items]
Total Operating Revenues	106,155	98,130	229,855	218,000
Net Income (Loss)	15,433	13,306	33,019	29,488
Identifiable Assets	2,259,896		2,259,896		2,233,399
Manufacturing | Operating Segments
Segment Reporting Information [Line Items]
Total Operating Revenues	84,284	45,947	160,107	114,427
Net Income (Loss)	5,705	238	11,089	5,165
Identifiable Assets	220,896		220,896		191,005
Plastics | Operating Segments
Segment Reporting Information [Line Items]
Total Operating Revenues	95,169	48,679	157,356	95,076
Net Income (Loss)	22,544	$ 5,130	31,692	$ 10,579
Identifiable Assets	$ 136,604		$ 136,604		$ 99,767

Revenue (Details)

Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Total Operating Revenues	$ 285,608	$ 192,756	$ 547,318	$ 427,503
Operating Segments
Disaggregation of Revenue [Line Items]
Total Operating Revenues from Contracts with Customers	287,390	192,547	550,075	427,381
Operating Segments | Electric
Disaggregation of Revenue [Line Items]
Total Operating Revenues	106,155	98,130	229,855	218,000
Electric Segment - ARP Revenues	(1,782)	209	(2,757)	122
Operating Segments | Manufacturing
Disaggregation of Revenue [Line Items]
Total Operating Revenues	84,284	45,947	160,107	114,427
Operating Segments | Plastics
Disaggregation of Revenue [Line Items]
Total Operating Revenues	95,169	48,679	157,356	95,076
Operating Segments | Retail: Residential | Electric
Disaggregation of Revenue [Line Items]
Total Operating Revenues	28,709	27,862	66,176	63,705
Operating Segments | Retail: Commercial and Industrial | Electric
Disaggregation of Revenue [Line Items]
Total Operating Revenues	58,390	55,914	124,811	124,853
Operating Segments | Retail: Other | Electric
Disaggregation of Revenue [Line Items]
Total Operating Revenues	1,888	1,777	3,706	3,598
Operating Segments | Total Retail | Electric
Disaggregation of Revenue [Line Items]
Total Operating Revenues	88,987	85,553	194,693	192,156
Operating Segments | Transmission | Electric
Disaggregation of Revenue [Line Items]
Total Operating Revenues	11,840	9,673	23,785	20,514
Operating Segments | Wholesale | Electric
Disaggregation of Revenue [Line Items]
Total Operating Revenues	3,260	765	7,767	1,641
Operating Segments | Other | Electric
Disaggregation of Revenue [Line Items]
Total Operating Revenues	2,068	2,139	3,610	3,689
Operating Segments | Metal Parts and Tooling | Manufacturing
Disaggregation of Revenue [Line Items]
Total Operating Revenues	71,013	37,266	133,686	94,478
Operating Segments | Plastic Products and Tooling | Manufacturing
Disaggregation of Revenue [Line Items]
Total Operating Revenues	10,131	7,840	20,426	17,723
Operating Segments | Scrap Metal Sales | Manufacturing
Disaggregation of Revenue [Line Items]
Total Operating Revenues	$ 3,140	$ 841	$ 5,995	$ 2,226

Select Balance Sheet Informat_3

Select Balance Sheet Information - Schedule of Receivables (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Trade	$ 135,744	$ 87,048
Other	12,252	8,939
Unbilled Receivables	18,154	21,187
Total Receivables	166,150	117,174
Less: Allowance for Credit Losses	2,726	3,215	$ 2,055	$ 1,339
Receivables, net of allowance for credit losses	$ 163,424	$ 113,959

Select Balance Sheet Informat_4

Select Balance Sheet Information - Summary of Activity in Allowance for Credit Losses (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance, January 1	$ 3,215	$ 1,339
Additions Charged to Expense	284	1,371
Reductions for Amounts Written-Off, Net of Recoveries	(773)	(655)
Ending Balance, June 30	$ 2,726	$ 2,055

Select Balance Sheet Informat_5

Select Balance Sheet Information - Schedule of Inventories (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Finished Goods	$ 21,272	$ 22,046
Work in Process	24,140	16,210
Raw Material, Fuel and Supplies	57,612	53,909
Inventories	$ 103,024	$ 92,165

Select Balance Sheet Informat_6

Select Balance Sheet Information - Schedule of Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Corporate-Owned Life Insurance Policies	$ 39,492	$ 36,825
Debt Securities	9,227	9,260
Money Market Funds	1,861	4,075
Mutual Funds	5,201	1,662
Other Investments	28	34
Total Investments	$ 55,809	$ 51,856

Select Balance Sheet Informat_7

Select Balance Sheet Information - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, net of accumulated depreciation	$ 2,073,009	$ 2,049,273
Electric Plant in Service
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,787,028	2,734,430
Less Accumulated Depreciation and Amortization	811,134	778,988
Property, Plant and Equipment, net of accumulated depreciation	1,975,894	1,955,442
Nonelectric Property, Plant and Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	274,001	268,020
Less Accumulated Depreciation and Amortization	176,886	174,189
Property, Plant and Equipment, net of accumulated depreciation	97,115	93,831
Electric Plant in Service | Electric Plant in Service
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,699,352	2,531,352
Construction Work in Progress | Electric Plant in Service
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	87,676	203,078
Construction Work in Progress | Nonelectric Property, Plant and Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	12,936	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	$ 261,065	$ 258,730

Regulatory Matters - Regulatory

Regulatory Matters - Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	$ 23,250	$ 21,900
Regulatory assets, long-term	160,018	168,395
Regulatory liabilities, current	17,301	16,663
Regulatory liabilities, long -term	231,766	233,973
Deferred Income Taxes
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities, current	0	0
Regulatory liabilities, long -term	131,893	134,719
Plant Removal Obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities, current	5,556	0
Regulatory liabilities, long -term	96,164	98,707
Fuel Clause Adjustments
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities, current	6,531	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	$ 3,094	3,581
Regulatory liabilities, long -term	1,761	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
Other
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities, current	$ 161	176
Regulatory liabilities, long -term	1,948	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	141,668	146,071
Alternative Revenue Program Riders
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	6,505	8,871
Regulatory assets, long-term	$ 8,982	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	6,696	8,462
ISO Cost Recovery Trackers
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	539	1,079
Regulatory assets, long-term	$ 724	867
Regulatory Assets - Remaining Recovery/Refund Period	2 years
Unrecovered Project Costs
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	$ 4,114	361
Regulatory assets, long-term	$ 1,492	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	$ 888	360
Regulatory assets, long-term	110	230
Debt Reacquisition Premiums
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory assets - current	167	192
Regulatory assets, long-term	$ 263	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	$ 83	$ 62

Short-Term and Long-Term Borr_3

Short-Term and Long-Term Borrowings - Lines of Credit (Details) - USD ($)	Jun. 30, 2021	Dec. 31, 2020
Line of Credit Facility [Line Items]
Line Limit	$ 340,000,000	$ 340,000,000
Amount Outstanding	127,957,000	80,997,000
Letters of Credit	12,671,000
Amount Available	199,372,000	244,902,000
OTC Credit Agreement
Line of Credit Facility [Line Items]
Line Limit	170,000,000	170,000,000
Amount Outstanding	59,245,000
Letters of Credit	0
Amount Available	110,755,000	104,834,000
OTP Credit Agreement
Line of Credit Facility [Line Items]
Line Limit	170,000,000	170,000,000
Amount Outstanding	68,712,000
Letters of Credit	12,671,000
Amount Available	$ 88,617,000	$ 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	Jun. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Long-term debt	$ 767,000	$ 767,169
Current Maturities Net of Unamortized Debt Issuance Costs	139,963	140,087
Unamortized Long-Term Debt Issuance Costs	2,497	2,650
Total Long-Term Debt Net of Unamortized Debt Issuance Costs	$ 624,540	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
	May 31, 2022USD ($)	Nov. 30, 2021USD ($)	Jun. 30, 2021USD ($)issuance	Jun. 10, 2021USD ($)	Dec. 31, 2020USD ($)
Debt Instrument [Line Items]
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
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%
Maximum
Debt Instrument [Line Items]
Debt to total capitalization ratio			60.00%
Minimum
Debt Instrument [Line Items]
Interest and dividend coverage ratio			1.50

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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost–Benefit Earned During the Period	$ 1,865	$ 1,656	$ 3,731	$ 3,311
Interest Cost on Projected Benefit Obligation	2,915	3,263	5,830	6,526
Expected Return on Assets	(5,589)	(5,505)	(11,179)	(11,010)
Amortization of Net Actuarial Loss:
From Regulatory Asset	2,661	2,231	5,321	4,462
From Other Comprehensive Income	68	55	136	110
Net Periodic Pension Cost	1,920	1,700	3,839	3,399
Executive Survivor and Supplemental Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost–Benefit Earned During the Period	46	44	93	89
Interest Cost on Projected Benefit Obligation	307	362	614	724
Amortization of Net Actuarial Loss:
From Regulatory Asset	31	24	62	47
From Other Comprehensive Income	125	85	249	171
Net Periodic Pension Cost	509	515	1,018	1,031
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost–Benefit Earned During the Period	431	462	861	924
Interest Cost on Projected Benefit Obligation	473	599	946	1,197
Amortization of Prior Service Cost:
From Regulatory Asset	(1,398)	(1,170)	(2,795)	(2,339)
From Other Comprehensive Income	(36)	(29)	(72)	(58)
Amortization of Net Actuarial Loss:
From Regulatory Asset	920	1,052	1,840	2,103
From Other Comprehensive Income	24	26	47	52
Net Periodic Pension Cost	$ 414	$ 940	$ 827	$ 1,879

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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 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)	(6.30%)	0.00%	(6.80%)	0.00%
Amortization of Excess Deferred Income Taxes	(2.00%)	(3.40%)	(2.40%)	(3.80%)
North Dakota Wind Tax Credit Amortization, Net of Federal Tax	(0.30%)	(1.20%)	(0.30%)	(1.00%)
Excess Tax Deduction on Stock Awards	0.00%	(0.60%)	0.00%	(1.00%)
Allowance for Equity Funds Used During Construction	(0.10%)	(0.80%)	(0.10%)	(1.00%)
Other, Net	(0.80%)	(1.70%)	(0.60%)	(0.60%)
Effective Tax Rate	16.50%	18.30%	15.80%	18.60%

Commitments and Contingencies (

Commitments and Contingencies (Details) $ in Millions	6 Months Ended
	Jun. 30, 2021USD ($)
Pending Litigation | Westmoreland Arbitration
Other Commitments [Line Items]
Recovery sought	$ 5.5
Otter Tail Power Company | Coyote Station [Member]
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	$ 3.5

Stockholders' Equity (Details)

Stockholders' Equity (Details) - USD ($) $ in Thousands	May 03, 2021	Jul. 15, 2020	Jun. 30, 2021	Dec. 31, 2020
Class of Stock [Line Items]
Total capitalization			$ 1,539,663	$ 1,495,398
Otter Tail Power Company
Class of Stock [Line Items]
Equity to total capitalization ratio			52.10%
Net assets restricted from distribution			$ 682,000
Minimum | Minnesota Public Utilities Commission | Otter Tail Power Company
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 | Minnesota Public Utilities Commission | Otter Tail Power Company
Class of Stock [Line Items]
Public utilities, requested equity capital structure, percentage		58.10%
Second Shelf Registration
Class of Stock [Line Items]
Shelf registration, shares	1,500,000

Share-Based Payments - Narrativ

Share-Based Payments - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment arrangement, expense	$ 1.3	$ 1.2	$ 5.5	$ 4
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)	6 Months Ended
	Jun. 30, 2021$ / sharesshares
Stock Awards
Shares
Beginning of year (in shares) | shares	128,664
Granted (in shares) | shares	57,650
Vested (in shares) | shares	(46,371)
Forfeited (in shares) | shares	(1,577)
End of year (in shares) | shares	138,366
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	43.04
Forfeited (in dollars per share) | $ / shares	40.77
End of year (in dollars per share) | $ / shares	$ 44.26
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	6 Months Ended
	Jun. 30, 2021	Jun. 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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Weighted Average Common Shares Outstanding - Basic (in shares)	41,500	40,513	41,478	40,365
Effect of Dilutive Securities:
Total Dilutive Shares (in shares)	318	164	281	196
Weighted Average Common Shares Outstanding – Diluted (in shares)	41,818	40,677	41,759	40,561
Stock Performance Awards
Effect of Dilutive Securities:
Effect of Dilutive Securities (in shares)	223	97	183	112
Stock Awards
Effect of Dilutive Securities:
Effect of Dilutive Securities (in shares)	75	47	80	56
Employee Stock Purchase Plan Shares and Other
Effect of Dilutive Securities:
Effect of Dilutive Securities (in shares)	20	20	18	28

Derivative Instruments (Details

Derivative Instruments (Details) - Swap $ in Millions	Jun. 30, 2021USD ($)MWh
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount of outstanding swap agreements | MWh	356,200
Fair value of outstanding swap agreements | $	$ 1.9

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Fair Value Measurements, Recurring and Nonrecurring (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities	$ 9,227	$ 9,260
Level 1 | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money Market Funds	1,861	4,075
Mutual Funds	5,201	1,662
Total Assets	7,062	5,737
Level 2 | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Instruments	1,879
Total Assets	11,107	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	2,393	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	$ 6,835	$ 6,633

Fair Value Measurements - Sch_2

Fair Value Measurements - Schedule of Fair Value of Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents	$ 1,480	$ 1,163
Short-Term Debt	(127,957)	(80,997)
Long-Term Debt	(764,503)	(764,519)
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents	1,480	1,163
Short-Term Debt	(127,957)	(80,997)
Long-Term Debt	$ (875,405)	$ (858,455)