Note 12 - Fair Value of Financial Instruments (Details) - Fair Value Hierarchy of Financial Instruments - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Financial Assets
Cash and due from banks	$ 192,642	$ 180,130
Short-term investments	432,384	536,880
Securities available-for-sale	1,485,124	1,586,352
Loans held-for-sale		6,676
Loans, net	10,142,747	9,938,810
Investment in Federal Home Loan Bank stock	17,250	17,250
Warrants	94	62
Financial Liabilities
Deposits	10,331,030	10,509,879
Securities sold under agreement to repurchase	413,195	413,417
Advances from Federal Home Loan Bank	475,128	274,488
Other borrowings	15,478	16,684
Long-term debt	58,951	58,420
Fair Value, Inputs, Level 1 [Member]
Financial Assets
Cash and due from banks	192,642	180,130
Short-term investments	432,384	536,880
Securities available-for-sale	230,719	290,121
Fair Value, Inputs, Level 2 [Member]
Financial Assets
Securities available-for-sale	1,254,405	1,296,231
Investment in Federal Home Loan Bank stock	17,250	17,250
Financial Liabilities
Securities sold under agreement to repurchase	413,195	413,417
Advances from Federal Home Loan Bank	475,128
Long-term debt	58,951	58,420
Fair Value, Inputs, Level 3 [Member]
Financial Assets
Loans held-for-sale		6,676
Loans, net	10,142,747	9,938,810
Warrants	94	62
Financial Liabilities
Deposits	10,331,030	10,509,879
Advances from Federal Home Loan Bank		274,488
Other borrowings	$ 15,478	$ 16,684