Retained Earnings Restriction (Detail Textuals) (USD $) In Thousands, unless otherwise specified			6 Months Ended
Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Otter Tail Power Company	Jun. 30, 2013 Otter Tail Power Company Minimum	Jun. 30, 2013 Otter Tail Power Company Maximum
Retained Earnings Restriction [Line Items]
Required equity-to-total-capitalization ratio to limit dividend payment				44.80%	54.80%
Equity to total capitalization ratio			52.30%
Total Capitalization	$ 962,579	$ 959,154			$ 874,000

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.

No definition available.

Name:	ottr_EquityToTotalCapitalizationRatio
Namespace Prefix:	ottr_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration