Composition of loans held-in-portfolio-covered loans (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered Loans	$ 3,076,009	$ 3,755,972
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered Loans	1,725,153	2,077,411
Commercial And Industrial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered Loans	128,698	167,236
Commercial Real Estate Construction Financing Receivable Member
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered Loans	201,437	361,396
Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered Loans	965,779	1,076,730
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered Loans	$ 54,942	$ 73,199