Loans - Risk Category of Loans (Detail) (Non-PCI Loans [Member], USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	$ 6,098,394	$ 6,004,682
Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	1,800,818	1,832,743
Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	3,893,492	3,772,084
Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	404,084	399,855
Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	5,677,964	5,577,491
Pass [Member] | Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	1,634,931	1,673,604
Pass [Member] | Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	3,696,473	3,563,530
Pass [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	346,560	340,357
Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	164,094	156,769
Special Mention [Member] | Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	70,190	64,777
Special Mention [Member] | Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	60,107	59,175
Special Mention [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	33,797	32,817
Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	250,509	263,084
Substandard [Member] | Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	95,670	94,184
Substandard [Member] | Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	136,912	149,379
Substandard [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	17,927	19,521
Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	5,827	7,338
Doubtful [Member] | Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	27	178
Doubtful [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	$ 5,800	$ 7,160