Note 14 - Fair Value of Financial Instruments - Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2020		Dec. 31, 2019
Equity securities	$ 22,964		$ 28,005
Warrants	3,992		2,181
Foreign exchange contracts with gain	107,071		146,397
Foreign exchange contracts with gain, fair value	3,236		2,411
Interest rate swaps	72,717		130,401
Interest rate swaps, fair value	3,992		2,181
Option contracts	850		908
Option contracts, fair value	6		7
Foreign exchange contracts with loss	160,489		127,003
Foreign exchange contracts with loss, fair value	1,592		1,415
Interest rate swaps	686,785		602,291
Interest rate swaps, fair value	31,525		14,229
Commitments to extend credit	3,033,685		3,077,081
Commitments to extend credit, fair value	(8,847)		(9,826)
Standby letters of credit	255,173		282,352
Standby letters of credit, fair value	(1,647)		(2,431)
Other letters of credit	24,591		22,209
Other letters of credit, fair value	(21)		(20)
Bill of lading guarantees	221		319
Bill of lading guarantees, fair value	0		(1)
Reported Value Measurement [Member]
Cash and due from banks	128,896		177,240
Short-term investments	1,305,170		416,538
Securities available-for-sale	1,080,540		1,451,842
Loans, net	15,382,439		14,951,631
Equity securities	22,964		28,005
Investment in Federal Home Loan Bank stock	17,250		18,090
Deposits	16,034,248		14,692,308
Short-term borrowings	0		25,683
Advances from Federal Home Loan Bank	230,000		670,000
Other borrowings	23,788		36,666
Long-term debt	119,136		119,136
Reported Value Measurement [Member] | Warrants [Member]
Warrants	20		39
Estimate of Fair Value Measurement [Member]
Cash and due from banks	128,896		177,240
Short-term investments	1,305,170		416,538
Securities available-for-sale	1,080,540		1,451,842
Loans, net	16,030,529	[1]	15,444,752
Equity securities	22,964		28,005
Investment in Federal Home Loan Bank stock	17,250		18,090
Deposits	16,061,257		14,719,452
Short-term borrowings	0		25,683
Advances from Federal Home Loan Bank	238,509		674,530
Other borrowings	19,550		30,764
Long-term debt	64,296		76,058
Estimate of Fair Value Measurement [Member] | Warrants [Member]
Warrants	$ 20		$ 39

[1] In accordance with the prospective adoption of ASU 2016-01, the fair value of loans as of December 31, 2019 & 2018 was measured using an exit price notion.