Note 8 - Retained Earnings Restriction (Details Textual) - USD ($)		6 Months Ended
	May 01, 2017	Jun. 30, 2017	Dec. 31, 2016
Capitalization, Long-term Debt and Equity		$ 1,176,790,000	$ 1,175,445,000
OTP [Member]
Net Assets Restricted from Distribution		$ 452,000,000
Equity to Total Capitalization Ratio		52.40%
OTP [Member] | Minimum [Member]
Equity to Total Capitalization Ratio	47.40%	47.50%
OTP [Member] | Maximum [Member]
Capitalization, Long-term Debt and Equity	$ 1,178,024,000	$ 1,123,168,000
Equity to Total Capitalization Ratio	58.00%	58.10%