Composition of loans held-in-portfolio-covered loans (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered Loans	$ 3,199,998	$ 3,755,972
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered Loans	1,786,091	2,077,411
Commercial And Industrial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered Loans	114,379	167,236
Commercial Real Estate Construction Financing Receivable Member
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered Loans	240,365	361,396
Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered Loans	999,578	1,076,730
Consumer Portfolio Segment Member
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered Loans	$ 59,585	$ 73,199