Common Shares and Earnings Per Share (Detail Textuals) (USD $)	3 Months Ended	6 Months Ended
Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Stockholders Equity and Earnings Per Share [Abstract]
Maximum per share differences between basic and diluted earnings per share In total or from continuing or discontinued operations	$ 0.01	$ 0.01	$ 0.01	$ 0.01

Represents the maximum per share differences between basic and diluted earnings per share in total or from continuing or discontinued operations.

No definition available.

Name:	ottr_MaximumPerShareDifferencesBetweenBasicAndDilutedEarningsPerShareInTotalOrFromContinuingOrDiscontinuedOperations
Namespace Prefix:	ottr_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration