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	Sep. 30, 2012	Dec. 31, 2011
Financing receivable - total loans	$ 5,434,955	$ 5,348,615
Commercial And Industrial [Member]
Financing receivable - current	1,578,417	1,415,165
Financing receivable - 30-89 days past due	4,054	13,731
Financing receivable - 90 days or more past due	27,698	29,550
Financing receivable - total past due	31,752	43,281
Financing receivable - total loans	1,610,169	1,458,446
Financing receivable - non-accrual loans	31,102	44,152
Financing receivable - 90 days past due loans, still accruing interest	2,885	4,991
Agricultural [Member]
Financing receivable - current	258,330	242,727
Financing receivable - 30-89 days past due	373	30
Financing receivable - 90 days or more past due	1,084	1,019
Financing receivable - total past due	1,457	1,049
Financing receivable - total loans	259,787	243,776
Financing receivable - non-accrual loans	1,204	1,019
Office Retail And Industrial [Member]
Financing receivable - current	1,303,021	1,276,920
Financing receivable - 30-89 days past due	5,089	2,931
Financing receivable - 90 days or more past due	22,221	19,231
Financing receivable - total past due	27,310	22,162
Financing receivable - total loans	1,330,331	1,299,082
Financing receivable - non-accrual loans	22,624	30,043
Financing receivable - 90 days past due loans, still accruing interest	439	1,040
Multi-Family [Member]
Financing receivable - current	307,358	281,943
Financing receivable - 30-89 days past due	414	1,121
Financing receivable - 90 days or more past due	1,737	5,272
Financing receivable - total past due	2,151	6,393
Financing receivable - total loans	309,509	288,336
Financing receivable - non-accrual loans	2,028	6,487
Financing receivable - 90 days past due loans, still accruing interest	219
Residential Construction [Member]
Financing receivable - current	56,015	87,606
Financing receivable - 30-89 days past due	1,155	2,164
Financing receivable - 90 days or more past due	4,750	16,066
Financing receivable - total past due	5,905	18,230
Financing receivable - total loans	61,920	105,836
Financing receivable - non-accrual loans	4,750	18,076
Commercial Construction [Member]
Financing receivable - current	128,389	129,310
Financing receivable - 30-89 days past due	86	320
Financing receivable - 90 days or more past due	8,034	15,279
Financing receivable - total past due	8,120	15,599
Financing receivable - total loans	136,509	144,909
Financing receivable - non-accrual loans	4,423	23,347
Financing receivable - 90 days past due loans, still accruing interest	3,611
Other Commercial Real Estate [Member]
Financing receivable - current	756,931	849,066
Financing receivable - 30-89 days past due	8,067	6,372
Financing receivable - 90 days or more past due	15,714	32,708
Financing receivable - total past due	23,781	39,080
Financing receivable - total loans	780,712	888,146
Financing receivable - non-accrual loans	21,284	51,447
Financing receivable - 90 days past due loans, still accruing interest	1,313	1,707
Total Commercial Real Estate [Member]
Financing receivable - current	2,551,714	2,624,845
Financing receivable - 30-89 days past due	14,811	12,908
Financing receivable - 90 days or more past due	52,456	88,556
Financing receivable - total past due	67,267	101,464
Financing receivable - total loans	2,618,981	2,726,309
Financing receivable - non-accrual loans	55,109	129,400
Financing receivable - 90 days past due loans, still accruing interest	5,582	2,747
Total Corporate Loans [Member]
Financing receivable - current	4,388,461	4,282,737
Financing receivable - 30-89 days past due	19,238	26,669
Financing receivable - 90 days or more past due	81,238	119,125
Financing receivable - total past due	100,476	145,794
Financing receivable - total loans	4,488,937	4,428,531
Financing receivable - non-accrual loans	87,415	174,571
Financing receivable - 90 days past due loans, still accruing interest	8,467	7,738
Home Equity1 [Member]
Financing receivable - current	384,831	402,842
Financing receivable - 30-89 days past due	5,841	6,112
Financing receivable - 90 days or more past due	6,834	7,240
Financing receivable - total past due	12,675	13,352
Financing receivable - total loans	397,506	416,194
Financing receivable - non-accrual loans	6,262	7,407
Financing receivable - 90 days past due loans, still accruing interest	1,989	1,138
1-4 Family Mortgages [Member]
Financing receivable - current	283,492	192,646
Financing receivable - 30-89 days past due	2,042	3,712
Financing receivable - 90 days or more past due	7,374	4,741
Financing receivable - total past due	9,416	8,453
Financing receivable - total loans	292,908	201,099
Financing receivable - non-accrual loans	5,901	5,322
Financing receivable - 90 days past due loans, still accruing interest	2,050
Installment Loans [Member]
Financing receivable - current	38,638	41,288
Financing receivable - 30-89 days past due	279	625
Financing receivable - 90 days or more past due	77	376
Financing receivable - total past due	356	1,001
Financing receivable - total loans	38,994	42,289
Financing receivable - non-accrual loans	1	25
Financing receivable - 90 days past due loans, still accruing interest	76	351
Consumer [Member]
Financing receivable - current	706,961	636,776
Financing receivable - 30-89 days past due	8,162	10,449
Financing receivable - 90 days or more past due	14,285	12,357
Financing receivable - total past due	22,447	22,806
Financing receivable - total loans	729,408	659,582
Financing receivable - non-accrual loans	12,164	12,754
Financing receivable - 90 days past due loans, still accruing interest	4,115	1,489
Total Loans Excluding Covered Loans [Member]
Financing receivable - current	5,095,422	4,919,513
Financing receivable - 30-89 days past due	27,400	37,118
Financing receivable - 90 days or more past due	95,523	131,482
Financing receivable - total past due	122,923	168,600
Financing receivable - total loans	5,218,345	5,088,113
Financing receivable - non-accrual loans	99,579	187,325
Financing receivable - 90 days past due loans, still accruing interest	12,582	9,227
Covered Loans [Member]
Financing receivable - current	158,800	195,289
Financing receivable - 30-89 days past due	9,365	7,853
Financing receivable - 90 days or more past due	48,445	57,360
Financing receivable - total past due	57,810	65,213
Financing receivable - total loans	216,610	260,502
Financing receivable - non-accrual loans	16,372	19,879
Financing receivable - 90 days past due loans, still accruing interest	34,554	43,347
Total Loans [Member]
Financing receivable - current	5,254,222	5,114,802
Financing receivable - 30-89 days past due	36,765	44,971
Financing receivable - 90 days or more past due	143,968	188,842
Financing receivable - total past due	180,733	233,813
Financing receivable - total loans	5,434,955	5,348,615
Financing receivable - non-accrual loans	115,951	207,204
Financing receivable - 90 days past due loans, still accruing interest	$ 47,136	$ 52,574