Loans - Risk Category of Loans (Detail) - Non-PCI Loans - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	$ 10,695,612	$ 8,833,775
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	2,357,018	2,156,549
Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	7,628,328	6,069,532
Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	710,266	607,694
Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	10,440,996	8,539,636
Pass | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	2,246,457	2,049,752
Pass | Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	7,486,469	5,893,354
Pass | Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	708,070	596,530
Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	102,107	148,624
Special Mention | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	44,316	68,243
Special Mention | Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	57,591	79,279
Special Mention | Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	200	1,102
Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	150,913	143,215
Substandard | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	64,649	36,254
Substandard | Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	84,268	96,899
Substandard | Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	1,996	10,062
Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	1,596	2,300
Doubtful | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	1,596	2,300
Doubtful | Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	0	0
Doubtful | Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	$ 0	$ 0