Note 13 - Fair Value of Financial Instruments - Fair Value of Financial Instruments (Details) - USD ($)		Jun. 30, 2018	Dec. 31, 2017
Cash and due from banks		$ 195,392,000	$ 247,056,000
Securities available-for-sale		1,475,949,000	1,333,626,000
Equity securities		23,131,000	28,100,000
Loans held for sale			8,000,000
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
Foreign exchange contracts with gain		62,687,000	108,530,000
Foreign exchange contracts with gain, fair value		389,000	1,832,000
Interest rate swaps		726,879,000	514,159,000
Interest rate swaps, fair value		14,801,000	5,218,000
Deposits		13,121,255,000	12,700,674,000
Securities sold under agreements 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
Option contracts		1,654,000	1,014,000
Option contracts, fair value		9,000	9,000
Foreign exchange contracts with loss		92,014,000	32,127,000
Foreign exchange contracts with loss, fair value		2,083,000	453,000
Interest rate swaps		23,655,000	145,399,000
Interest rate swaps, fair value		157,000	2,699,000
Commitments to extend credit		2,559,651,000	2,366,368,000
Commitments to extend credit, fair value		(2,389,000)	(7,224,000)
Standby letters of credit		169,823,000	140,814,000
Standby letters of credit, fair value		(1,787,000)	(1,805,000)
Other letters of credit		35,196,000	27,353,000
Other letters of credit, fair value		(28,000)	(52,000)
Bill of lading guarantees		1,440,000	24,000
Bill of lading guarantees, fair value		(1,000)	0
Warrants [Member]
Warrants		176,000
Reported Value Measurement [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		1,475,949,000	1,333,626,000
Equity securities		23,131,000
Loans held for sale			8,000,000
Loans, net (1)	[2]	13,223,590,000	12,743,766,000
Investment in Federal Home Loan Bank stock		17,250,000	23,085,000
Deposits		13,104,546,000	12,689,893,000
Securities sold under agreements to repurchase		50,000,000	100,000,000
Advances from Federal Home Loan Bank		480,000,000	430,000,000
Other borrowings		53,397,000	52,885,000
Long-term debt		194,136,000	194,136,000
Reported Value Measurement [Member] | Warrants [Member]
Warrants		176,000	91,000
Estimate of Fair Value Measurement [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		1,475,949,000	1,333,626,000
Equity securities		23,131,000
Loans held for sale			8,000,000
Loans, net (1)	[2]	13,190,937,000	12,663,049,000
Investment in Federal Home Loan Bank stock		17,250,000	23,085,000
Deposits		13,121,255,000	12,700,674,000
Securities sold under agreements 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
Estimate of Fair Value Measurement [Member] | Warrants [Member]
Warrants		$ 176,000	$ 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.

[2] 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.