Note 12 - Fair Value of Financial Instruments (Details) - Fair Value Hierarchy of Financial Instruments - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Financial Assets
Cash and due from banks	$ 166,933	$ 176,830
Short-term investments	48,711	489,614
Securities available-for-sale	1,545,699	1,318,935
Loans held-for-sale		1,225
Loans, net	9,271,167	8,688,072
Investment in Federal Home Loan Bank stock	17,250	30,785
Warrants	32	27
Financial Liabilities
Deposits	9,341,551	8,785,342
Securities sold under agreement to repurchase	419,915	473,816
Advances from Federal Home Loan Bank	210,020	424,974
Other borrowings	17,571	17,978
Long-term debt	59,015	59,425
Fair Value, Inputs, Level 1 [Member]
Financial Assets
Cash and due from banks	166,933	176,830
Short-term investments	48,711	489,614
Securities available-for-sale	305,954	669,870
Fair Value, Inputs, Level 2 [Member]
Financial Assets
Securities available-for-sale	1,239,745	649,065
Investment in Federal Home Loan Bank stock	17,250	30,785
Financial Liabilities
Securities sold under agreement to repurchase	419,915	473,816
Advances from Federal Home Loan Bank	210,020	424,974
Long-term debt	59,015	59,425
Fair Value, Inputs, Level 3 [Member]
Financial Assets
Loans held-for-sale		1,225
Loans, net	9,271,167	8,688,072
Warrants	32	27
Financial Liabilities
Deposits	9,341,551	8,785,342
Other borrowings	$ 17,571	$ 17,978