Note 3 - Investment Securities (Details) - Securities with Unrealized Losses (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013
Held-to-Maturity
Held-to-Maturity Securities Less Than 12 Months Estimated Fair Value	$ 391,086
Held-to-Maturity Securities Less Than 12 Months Gross Unrealized Losses	(14,416)
Held-to-Maturity Securities 12 Months or More Estimated Fair Value	104
Held-to-Maturity Securities 12 Months or More Gross Unrealized Losses	(26)
Held-to-Maturity Securities Estimated Fair Value	391,190
Held-to-Maturity Securities Gross Unrealized Losses	(14,442)
Available-for-Sale
Available-for-Sale Securities Less Than 12 Months Estimated Fair Value	160,301
Available-for-Sale Securities Less Than 12 Months Gross Unrealized Losses	(4,610)
Available-for-Sale Securities Estimated Fair Value	160,301
Available-for-Sale Securities Gross Unrealized Losses	(4,610)
US Government Agencies Debt Securities [Member]
Held-to-Maturity
Held-to-Maturity Securities Less Than 12 Months Estimated Fair Value	299,727
Held-to-Maturity Securities Less Than 12 Months Gross Unrealized Losses	(8,322)
Held-to-Maturity Securities 12 Months or More Estimated Fair Value	0
Held-to-Maturity Securities 12 Months or More Gross Unrealized Losses	0
Held-to-Maturity Securities Estimated Fair Value	299,727
Held-to-Maturity Securities Gross Unrealized Losses	(8,322)
Available-for-Sale
Available-for-Sale Securities Less Than 12 Months Estimated Fair Value	159,090
Available-for-Sale Securities Less Than 12 Months Gross Unrealized Losses	(4,599)
Available-for-Sale Securities Estimated Fair Value	159,090
Available-for-Sale Securities Gross Unrealized Losses	(4,599)
US States and Political Subdivisions Debt Securities [Member]
Held-to-Maturity
Held-to-Maturity Securities Less Than 12 Months Estimated Fair Value	91,359
Held-to-Maturity Securities Less Than 12 Months Gross Unrealized Losses	(6,094)
Held-to-Maturity Securities 12 Months or More Estimated Fair Value	104
Held-to-Maturity Securities 12 Months or More Gross Unrealized Losses	(26)
Held-to-Maturity Securities Estimated Fair Value	91,463
Held-to-Maturity Securities Gross Unrealized Losses	(6,120)
Available-for-Sale
Available-for-Sale Securities Less Than 12 Months Estimated Fair Value	1,211
Available-for-Sale Securities Less Than 12 Months Gross Unrealized Losses	(11)
Available-for-Sale Securities 12 Months or More Estimated Fair Value	0
Available-for-Sale Securities 12 Months or More Gross Unrealized Losses	0
Available-for-Sale Securities Estimated Fair Value	1,211
Available-for-Sale Securities Gross Unrealized Losses	$ (11)