Note 3 - Investment Securities (Details)	3 Months Ended				9 Months Ended
	Jun. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Note 3 - Investment Securities (Details) [Line Items]
Marketable Securities					$ 770,724,000		$ 795,978,000
Tax Expense Related to the Net Realized Gain On the Sale of Available-for-sale Securities					463,000	$ 9,000
Held-to-maturity Securities, Sold Security, at Carrying Value		$ 419,000				$ 419,000
Securities Pledged as Collateral [Member]
Note 3 - Investment Securities (Details) [Line Items]
Marketable Securities					$ 419,052,000		$ 369,951,000
US States and Political Subdivisions Debt Securities [Member]
Note 3 - Investment Securities (Details) [Line Items]
Held-to-maturity Securities, Sold Security, at Carrying Value	$ 235,000		$ 725,000
Held-to-maturity Securities, Sold Security, Realized Gain (Loss), Excluding Other than Temporary Impairments	$ 8,000	$ 22,000	$ 31,000
US States and Political Subdivisions Debt Securities [Member] | Held-to-maturity Securities [Member]
Note 3 - Investment Securities (Details) [Line Items]
Number of Securities Sold	1	1
Number of Issuers of Securities Sold			3
Collateralized Mortgage Backed Securities [Member]
Note 3 - Investment Securities (Details) [Line Items]
Held-to-maturity Securities, Sold Security, at Carrying Value				$ 1,200,000
Held-to-maturity Securities, Sold Security, Realized Gain (Loss), Excluding Other than Temporary Impairments				$ 66,000
Collateralized Mortgage Backed Securities [Member] | Held-to-maturity Securities [Member]
Note 3 - Investment Securities (Details) [Line Items]
Minimum Balance of Principal Collected Prior to Sale, Percentage		85.00%		85.00%
Excludes U.S. Government and Its Agencies [Member]
Note 3 - Investment Securities (Details) [Line Items]
Number of Holdings Greater Than 10% of Stockholders' Equity					0		0