Note 4 - Trading Account Assets (Details) - Trading Accounts Credit Ratings	6 Months Ended
	Jun. 30, 2015
Financing Receivable, Recorded Investment [Line Items]
Trading accounts credit ratings	100.00%
Moody's, Aaa Rating [Member]
Financing Receivable, Recorded Investment [Line Items]
Trading accounts credit ratings	8.00%
Moody's Aa1 - Aa3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Trading accounts credit ratings	60.00%
Moody's A1 - A3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Trading accounts credit ratings	22.00%
Not Rated [Member]
Financing Receivable, Recorded Investment [Line Items]
Trading accounts credit ratings	10.00%
Standard & Poor's, AAA Rating [Member]
Financing Receivable, Recorded Investment [Line Items]
Trading accounts credit ratings	14.00%
Standard and Poor's AA+ - AA- [Member]
Financing Receivable, Recorded Investment [Line Items]
Trading accounts credit ratings	57.00%
Standard and Poor's A+ - A- [Member]
Financing Receivable, Recorded Investment [Line Items]
Trading accounts credit ratings	18.00%
Not Rated [Member]
Financing Receivable, Recorded Investment [Line Items]
Trading accounts credit ratings	11.00%