Loans - Risk Category of Loans (Detail) - Non-PCI Loans - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	$ 11,107,646	$ 10,695,612
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	2,398,154	2,357,018
Commercial real estate loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	7,951,229	7,628,328
Commercial real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	758,263	710,266
Pass
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	10,796,739	10,440,996
Pass | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	2,226,553	2,246,457
Pass | Commercial real estate loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	7,814,338	7,486,469
Pass | Commercial real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	755,848	708,070
Special Mention
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	146,763	102,107
Special Mention | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	87,059	44,316
Special Mention | Commercial real estate loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	57,289	57,591
Special Mention | Commercial real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	2,415	200
Substandard
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	161,978	150,913
Substandard | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	82,376	64,649
Substandard | Commercial real estate loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	79,602	84,268
Substandard | Commercial real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	0	1,996
Doubtful
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	2,166	1,596
Doubtful | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	2,166	1,596
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