Loans - Risk Category of Loans (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Non-PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	$ 7,489,763	$ 6,748,933
Non-PCI Loans [Member] | Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	1,959,927	1,820,136
Non-PCI Loans [Member] | Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	5,053,742	4,521,920
Non-PCI Loans [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	476,094	406,877
Pass [Member] | Non-PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	7,223,802	6,411,735
Pass [Member] | Non-PCI Loans [Member] | Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	1,865,472	1,689,613
Pass [Member] | Non-PCI Loans [Member] | Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	4,903,185	4,348,642
Pass [Member] | Non-PCI Loans [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	455,145	373,480
Special Mention [Member] | Non-PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	92,608	115,863
Special Mention [Member] | Non-PCI Loans [Member] | Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	50,453	56,007
Special Mention [Member] | Non-PCI Loans [Member] | Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	40,232	48,159
Special Mention [Member] | Non-PCI Loans [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	1,923	11,697
Substandard [Member] | Non-PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	170,809	215,340
Substandard [Member] | Non-PCI Loans [Member] | Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	44,002	74,501
Substandard [Member] | Non-PCI Loans [Member] | Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	110,325	125,119
Substandard [Member] | Non-PCI Loans [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	16,482	15,720
Doubtful [Member] | Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	0
Doubtful [Member] | Non-PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	2,544	5,995
Doubtful [Member] | Non-PCI Loans [Member] | Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	0	15
Doubtful [Member] | Non-PCI Loans [Member] | Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans		0
Doubtful [Member] | Non-PCI Loans [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	$ 2,544	$ 5,980