Loans - Risk Category of Loans (Detail) - Non-PCI Loans - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	$ 9,655,820	$ 8,833,775
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	2,200,838	2,156,549
Commercial real estate loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	6,822,650	6,069,532
Commercial real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	632,332	607,694
Pass
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	9,403,506	8,539,636
Pass | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	2,114,575	2,049,752
Pass | Commercial real estate loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	6,666,210	5,893,354
Pass | Commercial real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	622,721	596,530
Special Mention
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	118,176	148,624
Special Mention | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	52,028	68,243
Special Mention | Commercial real estate loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	65,621	79,279
Special Mention | Commercial real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	527	1,102
Substandard
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	134,138	143,215
Substandard | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	34,235	36,254
Substandard | Commercial real estate loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	90,819	96,899
Substandard | Commercial real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	9,084	10,062
Doubtful
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	0	2,300
Doubtful | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	0	2,300
Doubtful | Commercial real estate loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	0	0
Doubtful | Commercial real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	$ 0	$ 0