Note 9 - Borrowed Funds (Details Textual)				12 Months Ended
	Nov. 23, 2014	Mar. 13, 2014 USD ($)	Nov. 23, 2004 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Securities Sold under Agreements to Repurchase				$ 350,000,000	$ 400,000,000
Weighted Average Rate Of Securities Sold Under Agreements				4.06%	3.89%
Debt, Weighted Average Interest Rate				4.01%	3.95%	3.92%
Debt Instrument, Basis Spread on Variable Rate	2.75%	3.50%
Advances from Federal Home Loan Banks				$ 350,000,000	$ 275,000,000
Threshold for Deferred Bonus			$ 225,000
Amount of Deferred Bonus Accrued in Other Liabilities		$ 300,000	$ 610,000
Accrued Interest on Deferred Bonus	5.06%	5.02%	7.00%
Interest Expense, Other				83,000	79,000	$ 93,000
Accrued Bonuses				1,700,000	1,600,000
Over-night Borrowings [Member]
Advances from Federal Home Loan Banks				$ 275,000,000	$ 250,000,000
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Interest Rate				0.55%	0.27%
Non Overnight Borrowings [Member]
Advances from Federal Home Loan Banks				$ 75,000,000	$ 25,000,000
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Interest Rate				1.48%	1.13%
Securities Sold under Agreements to Repurchase [Member]
Investment Securities Pledged As Collateral				$ 372,000,000	$ 430,200,000
Non Callable Fixed Rate Securities [Member]
Securities Sold under Agreements to Repurchase				$ 150,000,000	$ 200,000,000
Weighted Average Rate Of Securities Sold Under Agreements				2.81%	2.78%
Number Of Securities Sold Under Agreements To Repurchase				3	4
Non Callable Fixed Rate Securities [Member] | Mature in August 2016 [Member]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months				$ 50,000,000
Long-term Debt, Maturities, Repayments of Principal in Year Two				50,000,000
Long-term Debt, Maturities, Repayments of Principal in Year Three				$ 50,000,000
Floating to Fixed Rate Agreements Totaling 200 Million [Member]
Number Of Securities Sold Under Agreements To Repurchase				4
Total Floating to Fixed Rate				$ 200,000,000
Debt, Weighted Average Interest Rate				5.00%
Floating Interest Rate Range of Time Period				1 year
Floating to Fixed Rate Agreements Totaling 200 Million [Member] | Maximum [Member]
Debt Instrument, Interest Rate, Stated Percentage				5.07%
Floating to Fixed Rate Agreements Totaling 200 Million [Member] | Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument, Basis Spread on Variable Rate				3.40%
Floating to Fixed Rate Agreements Totaling 200 Million [Member] | Minimum [Member]
Debt Instrument, Interest Rate, Stated Percentage				4.89%
Mature in March 2018 [Member]
Advances from Federal Home Loan Banks				$ 25,000,000
Mature in December 2019 [Member]
Advances from Federal Home Loan Banks					$ 50,000,000
Treasury Note [Member]
Debt Instrument, Term	10 years	5 years