Note 12 - Fair Value of Financial Instruments (Details) - Fair Value of Financial Instruments - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Financial Assets
Cash and due from banks	$ 192,642	$ 180,130	$ 182,159	$ 176,830
Cash and due from banks	192,642	180,130
Short-term investments	432,384	536,880
Short-term investments	432,384	536,880
Securities available-for-sale	1,485,124	1,586,352
Loans held for sale		6,676
Loans held for sale		6,676
Loans, net	10,221,510	10,016,227
Loans, net	10,142,747	9,938,810
Investment in Federal Home Loan Bank stock	17,250	17,250
Investment in Federal Home Loan Bank stock	17,250	17,250
Warrants	94	62
Warrants	94	62
Foreign exchange contracts	138,201	100,602
Foreign exchange contracts	3,314	3,339
Financial Liabilities
Deposits	10,324,116	10,509,087
Deposits	10,331,030	10,509,879
Securities sold under agreements to repurchase	400,000	400,000
Securities sold under agreements to repurchase	413,195	413,417
Advances from Federal Home Loan Bank	475,000	275,000
Advances from Federal Home Loan Bank	475,128	274,488
Other borrowings	17,792	18,593
Other borrowings	15,478	16,684
Long-term debt	119,136	119,136
Long-term debt	58,951	58,420
Option contracts		9,396
Option contracts		28
Foreign exchange contracts	73,006	115,418
Foreign exchange contracts	913	4,124
Interest rate swaps	476,590	459,416
Interest rate swaps	14,878	6,496
Off-Balance Sheet Financial Instruments
Commitments to extend credit	2,098,360	1,971,848
Commitments to extend credit	(5,722)	(5,570)
Standby letters of credit	49,334	49,081
Standby letters of credit	(199)	(194)
Other letters of credit	30,883	38,131
Other letters of credit	(18)	(22)
Bill of lading guarantees	$ 52	454
Bill of lading guarantees		$ (1)