Note 16 - Fair Value of Financial Instruments - Fair Value Hierarchy of Financial Instruments (Details) - USD ($)		Dec. 31, 2018	Dec. 31, 2017
Cash and due from banks		$ 225,333,000	$ 247,056,000
Short-term investments		374,957,000	292,745,000
Securities available-for-sale		1,242,509,000	1,333,626,000
Loans, net (1)	[1]	13,928,162,000	12,663,049,000
Equity securities		25,098,000	28,100,000
Investment in Federal Home Loan Bank stock		17,250,000	23,085,000
Warrants		7,810,000	5,218,000
Deposits		13,754,028,000	12,700,674,000
Advances from Federal Home Loan Bank		529,500,000	429,482,000
Other borrowings		34,031,000	51,075,000
Long-term debt		132,615,000	141,865,000
Loans held-for-sale			8,000,000
Securities sold under agreement to repurchase			100,163,000
Warrants [Member]
Warrants		184,000
Warrants			91,000
Fair Value, Inputs, Level 1 [Member]
Cash and due from banks		225,333,000	247,056,000
Short-term investments		374,957,000	292,745,000
Securities available-for-sale		124,751,000	277,622,000
Loans, net (1)	[1]
Equity securities		25,098,000
Investment in Federal Home Loan Bank stock
Deposits
Advances from Federal Home Loan Bank
Other borrowings
Long-term debt
Loans held-for-sale
Securities sold under agreement to repurchase
Fair Value, Inputs, Level 1 [Member] | Warrants [Member]
Warrants
Warrants
Fair Value, Inputs, Level 2 [Member]
Cash and due from banks
Short-term investments
Securities available-for-sale		1,117,758,000	1,056,004,000
Loans, net (1)	[1]
Equity securities
Investment in Federal Home Loan Bank stock		17,250,000	23,085,000
Deposits
Advances from Federal Home Loan Bank		529,500,000	429,482,000
Other borrowings
Long-term debt		132,615,000	141,865,000
Loans held-for-sale
Securities sold under agreement to repurchase			100,163,000
Fair Value, Inputs, Level 2 [Member] | Warrants [Member]
Warrants
Warrants
Fair Value, Inputs, Level 3 [Member]
Cash and due from banks
Short-term investments
Securities available-for-sale
Loans, net (1)	[1]	13,928,162,000	12,663,049,000
Equity securities
Investment in Federal Home Loan Bank stock
Deposits		13,754,028,000	12,700,674,000
Advances from Federal Home Loan Bank
Other borrowings		34,031,000	51,075,000
Long-term debt
Loans held-for-sale			8,000,000
Securities sold under agreement to repurchase
Fair Value, Inputs, Level 3 [Member] | Warrants [Member]
Warrants		$ 184,000
Warrants			$ 91,000

[1] In accordance with the prospective adoption of ASU 2016-01, the fair value of loans as of December 31, 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.