Short-Term and Long-Term Borrowings (Detail textuals) (USD $)		6 Months Ended						1 Months Ended		1 Months Ended
	Jun. 30, 2013	Jun. 30, 2013 Cumulative Preferred Shares	Mar. 01, 2013 Cumulative Preferred Shares	Jun. 30, 2013 Maximum	Jun. 30, 2013 Minimum	Jun. 30, 2013 Otter Tail Power Company	Dec. 31, 2012 Otter Tail Power Company	Mar. 31, 2013 Otter Tail Power Company J P Morgan Chase Bank Unsecured Term Loan	Mar. 01, 2013 Otter Tail Power Company J P Morgan Chase Bank Unsecured Term Loan	Mar. 31, 2013 Otter Tail Power Company J P Morgan Chase Bank Unsecured Term Loan 4.65 % Grant County, South Dakota and 4.85 % Mercer County, North Dakota Pollution Control Refunding Revenue Bonds	Mar. 31, 2013 Otter Tail Power Company J P Morgan Chase Bank Unsecured Term Loan Intercompany Note
Debt Instrument [Line Items]
Short-term borrowings	$ 1,117,000					$ 1,117,000
Description of variable rate basis								LIBOR
Basis spread on variable rate									0.875%
Term loan borrowed for funding								40,900,000		25,100,000	15,700,000
Redemption amount of preferred stock equal to proceeds from term loan			15,700,000
Preferred stock redemption, call premiums		$ 200,000
Ratio of interest bearing debt to total capitalization				1.00	0.60