Note 12 - Fair Value of Financial Instruments (Details) - Fair Value of Financial Instruments (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
Financial Assets
Cash and due from banks	$ 161,657	$ 153,747	$ 155,525	$ 144,909
Securities available-for-sale	1,578,897	1,586,668
Trading securities		4,936
Investment in Federal Home Loan Bank stock	29,901	25,000
Deposits	8,232,625	7,981,305
Securities sold under agreements to repurchase	700,000	800,000
Advances from Federal Home Loan Bank	636,200	521,200
Long-term debt	121,136	121,136
Carrying Amount [Member]
Financial Assets
Cash and due from banks	161,657	153,747
Short-term investments	620,306	516,938
Short-term investments	620,306	516,938
Securities available-for-sale	1,578,897	1,586,668
Trading securities		4,936
Loans, net	8,120,208	7,897,187
Investment in Federal Home Loan Bank stock	29,901	25,000
Warrants	28	30
Option contracts	590	200
Foreign exchange contracts	270,675	267,644
Deposits	8,232,625	7,981,305
Securities sold under agreements to repurchase	700,000	800,000
Advances from Federal Home Loan Bank	636,200	521,200
Other borrowings	19,025	19,062
Long-term debt	121,136	121,136
Option contracts	590
Foreign exchange contracts	227,655	236,350
Off-Balance Sheet Financial Instruments
Commitments to extend credit	1,946,254	1,858,669
Standby letters of credit	48,825	45,058
Other letters of credit	51,704	54,098
Bill of lading guarantees	173	80
Fair Value [Member]
Financial Assets
Cash and due from banks	161,657	153,747
Short-term investments	620,306	516,938
Short-term investments	620,306	516,938
Securities available-for-sale	1,578,897	1,586,668
Trading securities		4,936
Loans, net	8,045,314	7,760,490
Investment in Federal Home Loan Bank stock	29,901	25,000
Warrants	28	30
Option contracts	3	0
Foreign exchange contracts	5,093	6,182
Deposits	8,233,462	7,977,639
Securities sold under agreements to repurchase	739,254	852,835
Advances from Federal Home Loan Bank	636,531	521,560
Other borrowings	16,337	16,107
Long-term debt	59,305	58,970
Option contracts	2
Foreign exchange contracts	3,322	6,140
Off-Balance Sheet Financial Instruments
Commitments to extend credit	(2,066)	(2,187)
Standby letters of credit	(210)	(205)
Other letters of credit	(34)	(34)
Bill of lading guarantees	$ 0	$ 0