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	Jun. 30, 2012	Dec. 31, 2011
Financing receivable - total loans	$ 5,528,073	$ 5,348,615
Commercial And Industrial [Member]
Financing receivable - current	1,536,959	1,415,165
Financing receivable - 30-89 days past due	14,364	13,731
Financing receivable - 90 days or more past due	46,104	29,550
Financing receivable - total past due	60,468	43,281
Financing receivable - total loans	1,597,427	1,458,446
Financing receivable - non-accrual loans	55,358	44,152
Financing receivable - 90 days past due loans, still accruing interest	2,565	4,991
Agricultural [Member]
Financing receivable - current	271,139	242,727
Financing receivable - 30-89 days past due	171	30
Financing receivable - 90 days or more past due	1,432	1,019
Financing receivable - total past due	1,603	1,049
Financing receivable - total loans	272,742	243,776
Financing receivable - non-accrual loans	1,293	1,019
Financing receivable - 90 days past due loans, still accruing interest	260
Office Retail And Industrial [Member]
Financing receivable - current	1,341,119	1,276,920
Financing receivable - 30-89 days past due	14,831	2,931
Financing receivable - 90 days or more past due	35,179	19,231
Financing receivable - total past due	50,010	22,162
Financing receivable - total loans	1,391,129	1,299,082
Financing receivable - non-accrual loans	46,629	30,043
Financing receivable - 90 days past due loans, still accruing interest	1,090	1,040
Multi-Family [Member]
Financing receivable - current	298,932	281,943
Financing receivable - 30-89 days past due	1,136	1,121
Financing receivable - 90 days or more past due	8,182	5,272
Financing receivable - total past due	9,318	6,393
Financing receivable - total loans	308,250	288,336
Financing receivable - non-accrual loans	8,843	6,487
Residential Construction [Member]
Financing receivable - current	71,021	87,606
Financing receivable - 30-89 days past due	2,821	2,164
Financing receivable - 90 days or more past due	15,066	16,066
Financing receivable - total past due	17,887	18,230
Financing receivable - total loans	88,908	105,836
Financing receivable - non-accrual loans	17,500	18,076
Commercial Construction [Member]
Financing receivable - current	123,200	129,310
Financing receivable - 30-89 days past due	1,945	320
Financing receivable - 90 days or more past due	22,481	15,279
Financing receivable - total past due	24,426	15,599
Financing receivable - total loans	147,626	144,909
Financing receivable - non-accrual loans	21,981	23,347
Financing receivable - 90 days past due loans, still accruing interest	500
Other Commercial Real Estate [Member]
Financing receivable - current	786,443	849,066
Financing receivable - 30-89 days past due	2,951	6,372
Financing receivable - 90 days or more past due	27,677	32,708
Financing receivable - total past due	30,628	39,080
Financing receivable - total loans	817,071	888,146
Financing receivable - non-accrual loans	34,192	51,447
Financing receivable - 90 days past due loans, still accruing interest	2,540	1,707
Total Commercial Real Estate [Member]
Financing receivable - current	2,620,715	2,624,845
Financing receivable - 30-89 days past due	23,684	12,908
Financing receivable - 90 days or more past due	108,585	88,556
Financing receivable - total past due	132,269	101,464
Financing receivable - total loans	2,752,984	2,726,309
Financing receivable - non-accrual loans	129,145	129,400
Financing receivable - 90 days past due loans, still accruing interest	4,130	2,747
Total Corporate Loans [Member]
Financing receivable - current	4,428,813	4,282,737
Financing receivable - 30-89 days past due	38,219	26,669
Financing receivable - 90 days or more past due	156,121	119,125
Financing receivable - total past due	194,340	145,794
Financing receivable - total loans	4,623,153	4,428,531
Financing receivable - non-accrual loans	185,796	174,571
Financing receivable - 90 days past due loans, still accruing interest	6,955	7,738
Home Equity1 [Member]
Financing receivable - current	388,337	402,842
Financing receivable - 30-89 days past due	3,689	6,112
Financing receivable - 90 days or more past due	6,402	7,240
Financing receivable - total past due	10,091	13,352
Financing receivable - total loans	398,428	416,194
Financing receivable - non-accrual loans	7,245	7,407
Financing receivable - 90 days past due loans, still accruing interest	779	1,138
1-4 Family Mortgages [Member]
Financing receivable - current	230,104	192,646
Financing receivable - 30-89 days past due	1,985	3,712
Financing receivable - 90 days or more past due	5,252	4,741
Financing receivable - total past due	7,237	8,453
Financing receivable - total loans	237,341	201,099
Financing receivable - non-accrual loans	5,466	5,322
Financing receivable - 90 days past due loans, still accruing interest	366
Installment Loans [Member]
Financing receivable - current	38,683	41,288
Financing receivable - 30-89 days past due	328	625
Financing receivable - 90 days or more past due	93	376
Financing receivable - total past due	421	1,001
Financing receivable - total loans	39,104	42,289
Financing receivable - non-accrual loans	1	25
Financing receivable - 90 days past due loans, still accruing interest	92	351
Consumer [Member]
Financing receivable - current	657,124	636,776
Financing receivable - 30-89 days past due	6,002	10,449
Financing receivable - 90 days or more past due	11,747	12,357
Financing receivable - total past due	17,749	22,806
Financing receivable - total loans	674,873	659,582
Financing receivable - non-accrual loans	12,712	12,754
Financing receivable - 90 days past due loans, still accruing interest	1,237	1,489
Total Loans Excluding Covered Loans [Member]
Financing receivable - current	5,085,937	4,919,513
Financing receivable - 30-89 days past due	44,221	37,118
Financing receivable - 90 days or more past due	167,868	131,482
Financing receivable - total past due	212,089	168,600
Financing receivable - total loans	5,298,026	5,088,113
Financing receivable - non-accrual loans	198,508	187,325
Financing receivable - 90 days past due loans, still accruing interest	8,192	9,227
Covered Loans [Member]
Financing receivable - current	175,844	195,289
Financing receivable - 30-89 days past due	7,900	7,853
Financing receivable - 90 days or more past due	46,303	57,360
Financing receivable - total past due	54,203	65,213
Financing receivable - total loans	230,047	260,502
Financing receivable - non-accrual loans	14,540	19,879
Financing receivable - 90 days past due loans, still accruing interest	33,288	43,347
Total Loans [Member]
Financing receivable - current	5,261,781	5,114,802
Financing receivable - 30-89 days past due	52,121	44,971
Financing receivable - 90 days or more past due	214,171	188,842
Financing receivable - total past due	266,292	233,813
Financing receivable - total loans	5,528,073	5,348,615
Financing receivable - non-accrual loans	213,048	207,204
Financing receivable - 90 days past due loans, still accruing interest	$ 41,480	$ 52,574