Note 3 - Investment Securities (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Securities Continuous Unrealized Loss Position Fair Value			$ 417,700,000
Securities Continuous Unrealized Loss Position Fair Value Percent of Portfolio			28.20%
Securities Sold under Agreements to Repurchase	$ 104,900,000		$ 104,900,000		$ 100,800,000
Available-for-sale Securities Pledged as Collateral	856,200,000		856,200,000		$ 520,400,000
Available-for-sale Securities, Gross Realized Gains	43,000		45,000	$ 191,000
Available-for-sale Securities, Gross Realized Losses	$ 3,000	$ 171,000	$ 43,000	$ 171,000
Marketable Securities, Realized Gain (Loss)		$ 153,000