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Stockholders' Equity (Details) - USD ($)			12 Months Ended	14 Months Ended
	Jul. 15, 2020	May 03, 2018	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Nov. 08, 2019
Class of Stock [Line Items]
Total capitalization			$ 1,495,398,000	$ 1,495,398,000	$ 1,471,063,000
Cumulative Preferred Shares
Equity [Abstract]
Preferred stock, shares authorized (in shares)			1,500,000	1,500,000
Preferred stock, shares outstanding (in shares)			0	0	0
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)			1,500,000	1,500,000
Preferred stock, shares outstanding (in shares)			0	0	0
Cumulative Preference Shares
Equity [Abstract]
Preferred stock, shares authorized (in shares)			1,000,000.0	1,000,000.0
Preferred stock, shares outstanding (in shares)			0	0
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)			1,000,000.0	1,000,000.0
Preferred stock, shares outstanding (in shares)			0	0
OTP
Class of Stock [Line Items]
Equity to total capitalization ratio			53.70%
Net assets restricted from distribution			$ 634,000,000	$ 634,000,000
Minimum | Minnesota Public Utilities Commission | OTP
Class of Stock [Line Items]
Public utilities, requested equity capital structure, percentage	47.50%
Maximum | OTP
Class of Stock [Line Items]
Total capitalization			1,700,000,000	1,700,000,000
Maximum | Minnesota Public Utilities Commission | OTP
Class of Stock [Line Items]
Public utilities, requested equity capital structure, percentage	58.10%
Distribution Agreement With KeyBanc
Class of Stock [Line Items]
Sale of stock, maximum aggregate sales price						$ 75,000,000.0
Net proceeds			37,000,000.0	$ 54,400,000
Commissions paid			$ 500,000
Number of shares issued (in shares)			868,484
Second Shelf Registration
Class of Stock [Line Items]
Net proceeds			$ 13,400,000
Number of shares issued (in shares)		1,500,000	320,173
Number of shares available for grant (in shares)			899,859	899,859

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- Definition

Represents the ratio of Equity to total capitalization, which includes as equity minority interest and preferred stock as well as all of the components of common equity as presented on the balance sheet. Total capitalization is calculated as equity plus short-term debt plus long-term debt as presented on the balance sheet.

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This element represents the total consolidated (as applicable) capitalization of the entity which is comprised of its long-term debt and equity instruments. The table may be detailed by subsidiary (legal entity) and include information by type of debt or equity detailed by instrument.

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The total of the cash outflow during the period which has been paid to third parties in connection with debt origination, which will be amortized over the remaining maturity period of the associated long-term debt and the cost incurred directly for the issuance of equity securities.

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Percentage of public utility's requested equity to capital, including debt and equity.

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