Note 12 - Fair Value of Financial Instruments (Detail) - Fair Value of Financial Instruments (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Financial Assets
Cash and due from banks	$ 155,525	$ 144,909	$ 119,106	$ 117,888
Securities held-to-maturity	773,768	773,768
Securities available-for-sale	2,190,296	1,291,480
Securities available-for-sale	2,190,296
Investment in Federal Home Loan Bank stock	37,130	41,272
Deposits	7,425,674	7,383,225
Securities sold under agreements to repurchase	1,150,000	1,250,000	1,250,000
Advances from Federal Home Loan Bank	126,200	146,200
Long-term debt	171,136	171,136
Carrying Amount [Member]
Financial Assets
Cash and due from banks	155,525	144,909
Short-term investments	215,794	411,983
Short-term investments	215,794	411,983
Securities held-to-maturity	0	773,768
Securities available-for-sale	2,190,296	1,291,480
Trading securities	4,758	4,703
Loans, net	7,175,462	7,235,587
Investment in Federal Home Loan Bank stock	37,130	41,272
Warrants	98	104
Option contracts	1,113	105
Foreign exchange contracts	211,674	188,145
Deposits	7,425,674	7,383,225
Securities sold under agreements to repurchase	1,150,000	1,250,000
Advances from Federal Home Loan Bank	126,200	146,200
Other borrowings	19,232	18,713
Long-term debt	171,136	171,136
Option contracts	465	104
Foreign exchange contracts	165,603	133,669
Off-Balance Sheet Financial Instruments
Commitments to extend credit	1,762,592	1,740,463
Standby letters of credit	45,814	44,672
Other letters of credit	57,750	71,073
Bill of lading guarantees	128	77
Fair Value [Member]
Financial Assets
Cash and due from banks	155,525	144,909
Short-term investments	215,794	411,983
Short-term investments	215,794	411,983
Securities held-to-maturity	0	823,906
Securities available-for-sale	2,190,296	1,291,480
Trading securities	4,758	4,703
Loans, net	7,119,348	7,169,732
Investment in Federal Home Loan Bank stock	37,130	41,272
Warrants	98	104
Option contracts	8	0
Foreign exchange contracts	2,987	2,924
Deposits	7,431,517	7,389,015
Securities sold under agreements to repurchase	1,244,735	1,361,585
Advances from Federal Home Loan Bank	126,962	146,789
Other borrowings	16,232	14,573
Long-term debt	101,715	98,392
Option contracts	2	2
Foreign exchange contracts	1,850	1,586
Off-Balance Sheet Financial Instruments
Commitments to extend credit	(1,867)	(1,875)
Standby letters of credit	(173)	(204)
Other letters of credit	(33)	(34)
Bill of lading guarantees	$ 0	$ 0