Note 6 - Pooled Trust Preferred Securities (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($) bank InsuranceCompany	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) bank InsuranceCompany	Jun. 30, 2017 USD ($)
Schedule Of Available For Sale Securities [Line Items]
Unrealized gains (losses)	$ 41,000		$ (205,000)
Realized OTTI credit loss			0
Total recognized OTTI credit loss	0	$ 0	$ 0	$ 0
PreTSL IV [Member]
Schedule Of Available For Sale Securities [Line Items]
Class			Mezzanine*
Investment securities available-for-sale, amortized cost	123,000		$ 123,000
Fair value	$ 118,000		118,000
Unrealized gains (losses)			(5,000)
Realized OTTI credit loss			0
Total recognized OTTI credit loss			$ (1,000)
Moody's/Fitch ratings			Ba1/BB
Current number of performing banks | bank	4		4
Current number of performing insurance companies | InsuranceCompany	0		0
Actual deferrals and defaults as a % of total collateral			0.00%
Total performing collateral as a % of outstanding bonds			185.40%