Note 13 - Fair Value of Financial Instruments - Fair Value Hierarchy of Financial Instruments (Details) - USD ($)		Jun. 30, 2018	Dec. 31, 2017
Cash and due from banks		$ 195,392,000	$ 247,056,000
Short-term investments and interest bearing deposits		208,749,000	292,745,000
Securities available-for-sale (amortized cost of $1,510,142 at June 30, 2018 and $1,336,345 at December 31, 2017)		1,475,949,000	1,333,626,000
Equity securities		23,131,000	28,100,000
Loans, net (1)	[1]	13,190,937,000	12,663,049,000
Investment in Federal Home Loan Bank stock		17,250,000	23,085,000
Warrants		14,801,000	5,218,000
Deposits		13,121,255,000	12,700,674,000
Securities sold under agreement to repurchase		50,041,000	100,163,000
Advances from Federal Home Loan Bank		479,511,000	429,482,000
Other borrowings		52,276,000	51,075,000
Long-term debt		141,473,000	141,865,000
Debt Securities, Available-for-sale, Total		1,475,949,000	1,333,626,000
Loans held-for-sale			8,000,000
Warrants [Member]
Warrants		176,000
Warrants			91,000
Fair Value, Inputs, Level 1 [Member]
Cash and due from banks		195,392,000	247,056,000
Short-term investments and interest bearing deposits		208,749,000	292,745,000
Securities available-for-sale (amortized cost of $1,510,142 at June 30, 2018 and $1,336,345 at December 31, 2017)		348,544,000	277,622,000
Equity securities		23,131,000
Loans, net (1)	[1]
Investment in Federal Home Loan Bank stock
Deposits
Securities sold under agreement to repurchase
Advances from Federal Home Loan Bank
Other borrowings
Long-term debt
Debt Securities, Available-for-sale, Total		348,544,000	277,622,000
Loans held-for-sale
Fair Value, Inputs, Level 1 [Member] | Warrants [Member]
Warrants
Warrants
Fair Value, Inputs, Level 2 [Member]
Cash and due from banks
Short-term investments and interest bearing deposits
Securities available-for-sale (amortized cost of $1,510,142 at June 30, 2018 and $1,336,345 at December 31, 2017)		1,127,405,000	1,056,004,000
Equity securities
Loans, net (1)	[1]
Investment in Federal Home Loan Bank stock		17,250,000	23,085,000
Deposits
Securities sold under agreement to repurchase		50,041,000	100,163,000
Advances from Federal Home Loan Bank		479,511,000	429,482,000
Other borrowings
Long-term debt		141,473,000	141,865,000
Debt Securities, Available-for-sale, Total		1,127,405,000	1,056,004,000
Loans held-for-sale
Fair Value, Inputs, Level 2 [Member] | Warrants [Member]
Warrants
Warrants
Fair Value, Inputs, Level 3 [Member]
Cash and due from banks
Short-term investments and interest bearing deposits
Securities available-for-sale (amortized cost of $1,510,142 at June 30, 2018 and $1,336,345 at December 31, 2017)
Equity securities
Loans, net (1)	[1]	13,190,937,000	12,663,049,000
Investment in Federal Home Loan Bank stock
Deposits		13,121,255,000	12,700,674,000
Securities sold under agreement to repurchase
Advances from Federal Home Loan Bank
Other borrowings		52,276,000	51,075,000
Long-term debt
Debt Securities, Available-for-sale, Total
Loans held-for-sale			8,000,000
Fair Value, Inputs, Level 3 [Member] | Warrants [Member]
Warrants		$ 176,000
Warrants			$ 91,000

[1] In accordance with the prospective adoption of ASU 2016-01, the fair value of loans as of June 30, 2018 was measured using an exit price notion. The fair value of loans as of December 31, 2017 was measured using an entry price notion.