Note 16 - Fair Value of Financial Instruments - Fair Value of Financial Instruments (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Cash and due from banks	$ 247,056,000	$ 218,017,000
Securities available-for-sale	1,333,626,000	1,314,345,000
Loans held for sale	8,000,000	7,500,000
Loans, net	12,663,049,000	11,006,344,000
Investment in Federal Home Loan Bank stock	23,085,000	17,250,000
Warrants	5,218,000	938,000
Foreign exchange contracts with gain	108,530,000	82,439,000
Foreign exchange contracts with gain, fair value	1,832,000	1,302,000
Interest rate swaps	514,159,000	361,526,000
Interest rate swaps, fair value	5,218,000	938,000
Deposits	12,700,674,000	11,680,017,000
Securities sold under agreements to repurchase	100,163,000	351,989,000
Advances from Federal Home Loan Bank	429,482,000	350,062,000
Other borrowings	51,075,000	15,944,000
Long-term debt	141,865,000	63,169,000
Option contracts	1,014,000	12,117,000
Option contracts, fair value	9,000	121,000
Foreign exchange contracts with loss	32,127,000	89,545,000
Foreign exchange contracts with loss, fair value	453,000	3,132,000
Interest rate swaps	145,399,000	119,136,000
Interest rate swaps, fair value	2,699,000	3,744,000
Commitments to extend credit	2,366,368,000	2,062,241,000
Commitments to extend credit, fair value	(7,224,000)	(6,025,000)
Standby letters of credit	140,814,000	75,396,000
Standby letters of credit, fair value	(1,805,000)	(668,000)
Other letters of credit	27,353,000	37,283,000
Other letters of credit, fair value	(52,000)	(16,000)
Bill of lading guarantees	24,000	75,000
Bill of lading guarantees, fair value	0	0
Warrants [Member]
Warrants	91,000
Reported Value Measurement [Member]
Cash and due from banks	247,056,000	218,017,000
Short-term investments	292,745,000	967,067,000
Securities available-for-sale	1,333,626,000	1,314,345,000
Loans held for sale	8,000,000	7,500,000
Loans, net	12,743,766,000	11,077,315,000
Investment in Federal Home Loan Bank stock	23,085,000	17,250,000
Deposits	12,689,893,000	11,674,726,000
Securities sold under agreements to repurchase	100,000,000	350,000,000
Advances from Federal Home Loan Bank	430,000,000	350,000,000
Other borrowings	52,885,000	17,662,000
Long-term debt	194,136,000	119,136,000
Reported Value Measurement [Member] | Warrants [Member]
Warrants	91,000	79,000
Estimate of Fair Value Measurement [Member]
Cash and due from banks	247,056,000	218,017,000
Short-term investments	292,745,000	967,067,000
Securities available-for-sale	1,333,626,000	1,314,345,000
Loans held for sale	8,000,000	7,500,000
Loans, net	12,663,049,000	11,006,344,000
Investment in Federal Home Loan Bank stock	23,085,000	17,250,000
Deposits	12,700,674,000	11,680,017,000
Securities sold under agreements to repurchase	100,163,000	351,989,000
Advances from Federal Home Loan Bank	429,482,000	350,062,000
Other borrowings	51,075,000	15,944,000
Long-term debt	141,865,000	63,169,000
Estimate of Fair Value Measurement [Member] | Warrants [Member]
Warrants	$ 91,000	$ 79,000