Allowance for Loan and Lease Losses on Covered Loans (Detail) (USD $) In Thousands	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2009
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending allowance on loans acquired with deteriorated credit quality (ASC 310-30)	$ 51,044		$ 16,493
Ending allowance on acquired loans outside the scope of ASC 310-30	0		0
Ending allowance on covered loans	51,044	31,555	16,493	11,583	1,273	0	0
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending allowance on loans acquired with deteriorated credit quality (ASC 310-30)	24,548		8,787
Ending allowance on acquired loans outside the scope of ASC 310-30	0		0
Ending allowance on covered loans	24,548		8,787
Real estate-commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending allowance on loans acquired with deteriorated credit quality (ASC 310-30)	24,773		7,213
Ending allowance on acquired loans outside the scope of ASC 310-30	0		0
Ending allowance on covered loans	24,773		7,213
Real estate-residential
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending allowance on loans acquired with deteriorated credit quality (ASC 310-30)	1,547		232
Ending allowance on acquired loans outside the scope of ASC 310-30	0		0
Ending allowance on covered loans	1,547		232
Installment
Financing Receivable, Allowance for Credit Losses [Line Items]
Ending allowance on loans acquired with deteriorated credit quality (ASC 310-30)	176		261
Ending allowance on acquired loans outside the scope of ASC 310-30	0		0
Ending allowance on covered loans	$ 176		$ 261