Note 3 - Investment Securities (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Securities Continuous Unrealized Loss Position Fair Value	$ 983,100,000
Securities Continuous Unrealized Loss Position Fair Value Percent of Portfolio	61.10%
Securities Sold under Agreements to Repurchase	$ 105,700,000		$ 105,700,000		$ 100,800,000
Available-for-sale Securities Pledged as Collateral	819,600,000		819,600,000		$ 520,400,000
Available-for-sale Securities, Gross Realized Gains	0		2,000
Available-for-sale Securities, Gross Realized Losses	$ 0		$ 40,000
Marketable Securities, Realized Gain (Loss)		$ 38,000		$ 3