Note 6 - Past Due Loans, Allowance For Credit Losses, and Impaired Loans (Detail) - Credit Quality Indicators by Class, Excluding Covered Loans (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Commercial Loan [Member] | Pass [Member]
Credit Quality Indicators by Class	$ 1,558,932		$ 1,308,812
Commercial Loan [Member] | Special Mention [Member]
Credit Quality Indicators by Class	37,833	[1]	57,866	[1]
Commercial Loan [Member] | Substandard Accrual [Member]
Credit Quality Indicators by Class	8,768	[2]	47,616	[2]
Commercial Loan [Member] | Substandard Non-Accrual [Member]
Credit Quality Indicators by Class	25,941	[3]	44,152	[3]
Commercial Loan [Member] | Total [Member]
Credit Quality Indicators by Class	1,631,474		1,458,446
Agricultural [Member] | Pass [Member]
Credit Quality Indicators by Class	267,114		232,270
Agricultural [Member] | Special Mention [Member]
Credit Quality Indicators by Class	331	[1]	10,487	[1]
Agricultural [Member] | Substandard Accrual [Member]
Credit Quality Indicators by Class		[2]		[2]
Agricultural [Member] | Substandard Non-Accrual [Member]
Credit Quality Indicators by Class	1,173	[3]	1,019	[3]
Agricultural [Member] | Total [Member]
Credit Quality Indicators by Class	268,618		243,776
Office Retail And Industrial [Member] | Pass [Member]
Credit Quality Indicators by Class	1,235,950		1,147,026
Office Retail And Industrial [Member] | Special Mention [Member]
Credit Quality Indicators by Class	57,271	[1]	78,578	[1]
Office Retail And Industrial [Member] | Substandard Accrual [Member]
Credit Quality Indicators by Class	16,746	[2]	43,435	[2]
Office Retail And Industrial [Member] | Substandard Non-Accrual [Member]
Credit Quality Indicators by Class	23,224	[3]	30,043	[3]
Office Retail And Industrial [Member] | Total [Member]
Credit Quality Indicators by Class	1,333,191		1,299,082
Multi-Family [Member] | Pass [Member]
Credit Quality Indicators by Class	282,126		275,031
Multi-Family [Member] | Special Mention [Member]
Credit Quality Indicators by Class	1,921	[1]	5,803	[1]
Multi-Family [Member] | Substandard Accrual [Member]
Credit Quality Indicators by Class		[2]	1,015	[2]
Multi-Family [Member] | Substandard Non-Accrual [Member]
Credit Quality Indicators by Class	1,434	[3]	6,487	[3]
Multi-Family [Member] | Total [Member]
Credit Quality Indicators by Class	285,481		288,336
Residential Construction [Member] | Pass [Member]
Credit Quality Indicators by Class	33,392		48,806
Residential Construction [Member] | Special Mention [Member]
Credit Quality Indicators by Class	11,870	[1]	27,198	[1]
Residential Construction [Member] | Substandard Accrual [Member]
Credit Quality Indicators by Class	11,588	[2]	11,756	[2]
Residential Construction [Member] | Substandard Non-Accrual [Member]
Credit Quality Indicators by Class	4,612	[3]	18,076	[3]
Residential Construction [Member] | Total [Member]
Credit Quality Indicators by Class	61,462		105,836
Commercial Construction [Member] | Pass [Member]
Credit Quality Indicators by Class	95,567		92,568
Commercial Construction [Member] | Special Mention [Member]
Credit Quality Indicators by Class	14,340	[1]	23,587	[1]
Commercial Construction [Member] | Substandard Accrual [Member]
Credit Quality Indicators by Class	14,174	[2]	5,407	[2]
Commercial Construction [Member] | Substandard Non-Accrual [Member]
Credit Quality Indicators by Class	873	[3]	23,347	[3]
Commercial Construction [Member] | Total [Member]
Credit Quality Indicators by Class	124,954		144,909
Other Commerical Real Estate [Member] | Pass [Member]
Credit Quality Indicators by Class	712,702		746,213
Other Commerical Real Estate [Member] | Special Mention [Member]
Credit Quality Indicators by Class	14,056	[1]	73,058	[1]
Other Commerical Real Estate [Member] | Substandard Accrual [Member]
Credit Quality Indicators by Class	30,149	[2]	17,428	[2]
Other Commerical Real Estate [Member] | Substandard Non-Accrual [Member]
Credit Quality Indicators by Class	16,214	[3]	51,447	[3]
Other Commerical Real Estate [Member] | Total [Member]
Credit Quality Indicators by Class	773,121		888,146
Commercial Real Estate [Member] | Pass [Member]
Credit Quality Indicators by Class	2,359,737		2,309,644
Commercial Real Estate [Member] | Special Mention [Member]
Credit Quality Indicators by Class	99,458	[1]	208,224	[1]
Commercial Real Estate [Member] | Substandard Accrual [Member]
Credit Quality Indicators by Class	72,657	[2]	79,041	[2]
Commercial Real Estate [Member] | Substandard Non-Accrual [Member]
Credit Quality Indicators by Class	46,357	[3]	129,400	[3]
Commercial Real Estate [Member] | Total [Member]
Credit Quality Indicators by Class	2,578,209		2,726,309
Total Corporate Loans [Member] | Pass [Member]
Credit Quality Indicators by Class	4,185,783		3,850,726
Total Corporate Loans [Member] | Special Mention [Member]
Credit Quality Indicators by Class	137,622	[1]	276,577	[1]
Total Corporate Loans [Member] | Substandard Accrual [Member]
Credit Quality Indicators by Class	81,425	[2]	126,657	[2]
Total Corporate Loans [Member] | Substandard Non-Accrual [Member]
Credit Quality Indicators by Class	73,471	[3]	174,571	[3]
Total Corporate Loans [Member] | Total [Member]
Credit Quality Indicators by Class	$ 4,478,301		$ 4,428,531

[1] Loans categorized as special mention have potential weaknesses that deserve the close attention of management. If left uncorrected, these potential weaknesses may result in the deterioration of repayment prospects or in the credit position of the Company at some future date.

[2] Loans categorized as substandard/accrual continue to accrue interest, but exhibit a well-defined weakness or weaknesses that may jeopardize the liquidation of the debt. These loans continue to accrue interest because they are well secured and collection of principal and interest is expected within a reasonable time.

[3] Loans categorized as substandard/non-accrual exhibit a well-defined weakness or weaknesses that may jeopardize the liquidation of the debt and are characterized by the distinct possibility that the Company could sustain some loss if the deficiencies are not corrected.