Loan and Lease Finance Receivables and Allowance For Credit Losses - Loans Modified as Troubled Debt Restructuring (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012 SecurityLoan	Sep. 30, 2011 SecurityLoan	Sep. 30, 2012 SecurityLoan	Sep. 30, 2011 SecurityLoan
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, number of loans	11	5	28	20
Troubled debt restructurings, pre-modification outstanding recorded investment	$ 9,331	$ 3,071	$ 33,480	$ 47,646
Troubled debt restructurings, post-modifications outstanding recorded investment	9,698	3,071	33,847	47,345
Troubled debt restructurings, outstanding recorded investment	10,831	3,007	33,344	41,667
Non-Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, number of loans	11	5	28	20
Troubled debt restructurings, pre-modification outstanding recorded investment	9,331	3,071	33,480	47,646
Troubled debt restructurings, post-modifications outstanding recorded investment	9,698	3,071	33,847	47,345
Troubled debt restructurings, outstanding recorded investment	10,831	3,007	33,344	41,667
Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, number of loans
Troubled debt restructurings, pre-modification outstanding recorded investment
Troubled debt restructurings, post-modifications outstanding recorded investment
Troubled debt restructurings, outstanding recorded investment
Commercial and Industrial [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, number of loans	2		9	5
Troubled debt restructurings, pre-modification outstanding recorded investment	268		1,970	2,253
Troubled debt restructurings, post-modifications outstanding recorded investment	135		1,837	1,952
Troubled debt restructurings, outstanding recorded investment	121		1,344	1,610
Construction - Speculative [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, number of loans			1	2
Troubled debt restructurings, pre-modification outstanding recorded investment			10,966	16,886
Troubled debt restructurings, post-modifications outstanding recorded investment			10,966	16,886
Troubled debt restructurings, outstanding recorded investment			10,618	15,531
Construction - Non-Speculative [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, number of loans				1
Troubled debt restructurings, pre-modification outstanding recorded investment				9,219
Troubled debt restructurings, post-modifications outstanding recorded investment				9,219
Troubled debt restructurings, outstanding recorded investment				9,219
Commercial Real Estate - Owner-Occupied [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, number of loans	1		4	1
Troubled debt restructurings, pre-modification outstanding recorded investment	853		3,921	2,039
Troubled debt restructurings, post-modifications outstanding recorded investment	853		3,921	2,039
Troubled debt restructurings, outstanding recorded investment	853		3,916	1,971
Commercial Real Estate - Non-Owner-Occupied [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, number of loans	2	1	4	3
Troubled debt restructurings, pre-modification outstanding recorded investment	2,631	1,519	6,657	11,707
Troubled debt restructurings, post-modifications outstanding recorded investment	2,631	1,519	6,657	11,707
Troubled debt restructurings, outstanding recorded investment	2,588	1,519	6,190	10,272
Residential Real Estate (SFR 1-4) [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, number of loans		4		6
Troubled debt restructurings, pre-modification outstanding recorded investment		1,552		2,162
Troubled debt restructurings, post-modifications outstanding recorded investment		1,552		2,162
Troubled debt restructurings, outstanding recorded investment		1,488		2,079
Dairy and Livestock [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, number of loans	4		8	2
Troubled debt restructurings, pre-modification outstanding recorded investment	5,060		9,447	3,380
Troubled debt restructurings, post-modifications outstanding recorded investment	5,560		9,947	3,380
Troubled debt restructurings, outstanding recorded investment	6,797		10,804	985
Agribusiness [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, number of loans
Troubled debt restructurings, pre-modification outstanding recorded investment
Troubled debt restructurings, post-modifications outstanding recorded investment
Troubled debt restructurings, outstanding recorded investment
Municipal Lease Finance Receivables [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, number of loans	2		2
Troubled debt restructurings, pre-modification outstanding recorded investment	519		519
Troubled debt restructurings, post-modifications outstanding recorded investment	519		519
Troubled debt restructurings, outstanding recorded investment	472		472
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, number of loans
Troubled debt restructurings, pre-modification outstanding recorded investment
Troubled debt restructurings, post-modifications outstanding recorded investment
Troubled debt restructurings, outstanding recorded investment
Auto and Equipment Leases [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, number of loans
Troubled debt restructurings, pre-modification outstanding recorded investment
Troubled debt restructurings, post-modifications outstanding recorded investment
Troubled debt restructurings, outstanding recorded investment