Note 6 - Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Detail) - Aging Analysis of Past Due Loans and Non-Performing Loans by Class (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Total Loans	$ 5,348,615	$ 5,472,289
Commercial And Industrial [Member]
Current	1,415,165	1,428,841
30-89 Days Past Due	13,731	7,706
90 Days or More Past Due	29,550	29,356
Total Past Due	43,281	37,062
Total Loans	1,458,446	1,465,903
Non- accrual Loans	44,152	50,088
90 Days Past Due Loans, Still Accruing Interest	4,991	1,552
Agricultural [Member]
Current	242,727	225,007
30-89 Days Past Due	30	65
90 Days or More Past Due	1,019	2,684
Total Past Due	1,049	2,749
Total Loans	243,776	227,756
Non- accrual Loans	1,019	2,497
90 Days Past Due Loans, Still Accruing Interest		187
Office Retail And Industrial [Member]
Current	1,276,920	1,183,952
30-89 Days Past Due	2,931	4,009
90 Days or More Past Due	19,231	15,652
Total Past Due	22,162	19,661
Total Loans	1,299,082	1,203,613
Non- accrual Loans	30,043	19,573
90 Days Past Due Loans, Still Accruing Interest	1,040
Multi-Family [Member]
Current	281,943	345,018
30-89 Days Past Due	1,121	2,811
90 Days or More Past Due	5,272	2,033
Total Past Due	6,393	4,844
Total Loans	288,336	349,862
Non- accrual Loans	6,487	6,203
Residential Construction [Member]
Current	87,606	139,499
30-89 Days Past Due	2,164	1,320
90 Days or More Past Due	16,066	33,871
Total Past Due	18,230	35,191
Total Loans	105,836	174,690
Non- accrual Loans	18,076	52,122
90 Days Past Due Loans, Still Accruing Interest		200
Commercial Construction [Member]
Current	129,310	140,044
30-89 Days Past Due	320	4,000
90 Days or More Past Due	15,279	20,428
Total Past Due	15,599	24,428
Total Loans	144,909	164,472
Non- accrual Loans	23,347	28,685
Other Commercial Real Estate [Member]
Current	849,066	813,333
30-89 Days Past Due	6,372	9,091
90 Days or More Past Due	32,708	33,933
Total Past Due	39,080	43,024
Total Loans	888,146	856,357
Non- accrual Loans	51,447	40,605
90 Days Past Due Loans, Still Accruing Interest	1,707	345
Total Commercial Real Estate [Member]
Current	2,624,845	2,621,846
30-89 Days Past Due	12,908	21,231
90 Days or More Past Due	88,556	105,917
Total Past Due	101,464	127,148
Total Loans	2,726,309	2,748,994
Non- accrual Loans	129,400	147,188
90 Days Past Due Loans, Still Accruing Interest	2,747	545
Total Corporate Loans [Member]
Current	4,282,737	4,275,694
30-89 Days Past Due	26,669	29,002
90 Days or More Past Due	119,125	137,957
Total Past Due	145,794	166,959
Total Loans	4,428,531	4,442,653
Non- accrual Loans	174,571	199,773
90 Days Past Due Loans, Still Accruing Interest	7,738	2,284
Home Equity [Member]
Current	402,842	431,446
30-89 Days Past Due	6,112	4,715
90 Days or More Past Due	7,240	9,082
Total Past Due	13,352	13,797
Total Loans	416,194	445,243
Non- accrual Loans	7,407	7,948
90 Days Past Due Loans, Still Accruing Interest	1,138	1,870
1-4 Family Mortgages [Member]
Current	192,646	154,999
30-89 Days Past Due	3,712	2,523
90 Days or More Past Due	4,741	3,368
Total Past Due	8,453	5,891
Total Loans	201,099	160,890
Non- accrual Loans	5,322	3,902
90 Days Past Due Loans, Still Accruing Interest		4
Installment Loans [Member]
Current	41,288	50,899
30-89 Days Past Due	625	742
90 Days or More Past Due	376	133
Total Past Due	1,001	875
Total Loans	42,289	51,774
Non- accrual Loans	25	159
90 Days Past Due Loans, Still Accruing Interest	351	86
Total Consumer Loans [Member]
Current	636,776	637,344
30-89 Days Past Due	10,449	7,980
90 Days or More Past Due	12,357	12,583
Total Past Due	22,806	20,563
Total Loans	659,582	657,907
Non- accrual Loans	12,754	12,009
90 Days Past Due Loans, Still Accruing Interest	1,489	1,960
Total Loans Excluding Covered Loans [Member]
Current	4,919,513	4,913,038
30-89 Days Past Due	37,118	36,982
90 Days or More Past Due	131,482	150,540
Total Past Due	168,600	187,522
Total Loans	5,088,113	5,100,560
Non- accrual Loans	187,325	211,782
90 Days Past Due Loans, Still Accruing Interest	9,227	4,244
Covered Loans [Member]
Current	195,289	268,934
30-89 Days Past Due	7,853	18,445
90 Days or More Past Due	57,360	84,350
Total Past Due	65,213	102,795
Total Loans	260,502	371,729
Non- accrual Loans	19,879
90 Days Past Due Loans, Still Accruing Interest	43,347	84,350
Loans Total [Member]
Current	5,114,802	5,181,972
30-89 Days Past Due	44,971	55,427
90 Days or More Past Due	188,842	234,890
Total Past Due	233,813	290,317
Total Loans	5,348,615	5,472,289
Non- accrual Loans	207,204	211,782
90 Days Past Due Loans, Still Accruing Interest	$ 52,574	$ 88,594