Note 15 - Fair Value Measurements and Fair Value of Financial Instruments - Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2020		Dec. 31, 2019
Equity securities	$ 23,744		$ 28,005
Warrants	3,409		2,181
Foreign exchange contracts with gain	151,244		146,397
Foreign exchange contracts with gain, fair value	4,658		2,411
Interest rate swaps	96,889		130,401
Interest rate swaps, fair value	3,409		2,181
Option contracts	0		908
Option contracts, fair value	0		7
Foreign exchange contracts with loss	132,813		127,003
Foreign exchange contracts with loss, fair value	2,200		1,415
Interest rate swaps	679,648		602,291
Interest rate swaps, fair value	10,286		14,229
Commitments to extend credit	2,977,528		3,077,081
Commitments to extend credit, fair value	(8,432)		(9,826)
Standby letters of credit	234,200		282,352
Standby letters of credit, fair value	(1,630)		(2,431)
Other letters of credit	16,821		22,209
Other letters of credit, fair value	(16)		(20)
Bill of lading guarantees	238		319
Bill of lading guarantees, fair value	0		(1)
Reported Value Measurement [Member]
Cash and due from banks	138,616		177,240
Short-term investments	1,282,462		416,538
Securities available-for-sale	1,036,550		1,451,842
Loans, net	15,475,364		14,951,631
Equity securities	23,744		28,005
Investment in Federal Home Loan Bank stock	17,250		18,090
Deposits	16,109,401		14,692,308
Short-term borrowings	0		25,683
Advances from Federal Home Loan Bank	150,000		670,000
Other borrowings	23,714		36,666
Long-term debt	119,136		119,136
Reported Value Measurement [Member] | Warrants [Member]
Warrants	21		39
Estimate of Fair Value Measurement [Member]
Cash and due from banks	138,616		177,240
Short-term investments	1,282,462		416,538
Securities available-for-sale	1,036,550		1,451,842
Loans, net	16,103,471	[1]	15,444,752
Equity securities	23,744		28,005
Investment in Federal Home Loan Bank stock	17,250		18,090
Deposits	16,125,808		14,719,452
Short-term borrowings	0		25,683
Advances from Federal Home Loan Bank	155,133		674,530
Other borrowings	19,632		30,764
Long-term debt	65,487		76,058
Estimate of Fair Value Measurement [Member] | Warrants [Member]
Warrants	$ 21		$ 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.