Loans - Risk Category of Loans (Detail) - Non-PCI Loans - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	$ 10,116,057	$ 8,833,775
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	2,266,420	2,156,549
Commercial real estate loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	7,178,836	6,069,532
Commercial real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	670,801	607,694
Pass
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	9,841,454	8,539,636
Pass | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	2,158,585	2,049,752
Pass | Commercial real estate loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	7,015,861	5,893,354
Pass | Commercial real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	667,008	596,530
Special Mention
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	125,640	148,624
Special Mention | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	46,209	68,243
Special Mention | Commercial real estate loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	79,331	79,279
Special Mention | Commercial real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	100	1,102
Substandard
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	147,309	143,215
Substandard | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	59,972	36,254
Substandard | Commercial real estate loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	83,644	96,899
Substandard | Commercial real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	3,693	10,062
Doubtful
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	1,654	2,300
Doubtful | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	1,654	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