Stockholders' Equity (Details) - USD ($) $ in Thousands			3 Months Ended
	May 03, 2021	Jul. 15, 2020	Mar. 31, 2021	Dec. 31, 2020
Class of Stock [Line Items]
Total capitalization			$ 1,512,352	$ 1,495,398
Otter Tail Power Company
Class of Stock [Line Items]
Equity to total capitalization ratio			52.40%
Net assets restricted from distribution			$ 671,000
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 | Subsequent Event
Class of Stock [Line Items]
Number of shares issued (in shares)	1,500,000