Composition of loans held-in-portfolio-covered loans (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered Loans	$ 2,654,263	$ 2,984,427
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered Loans	1,591,718	1,710,229
Commercial And Industrial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered Loans	104,933	102,575
Commercial Real Estate Construction Financing Receivable Member
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered Loans	74,468	190,127
Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered Loans	846,472	934,373
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered Loans	$ 36,672	$ 47,123