Loans - Risk Category of Loans (Detail) - Non-PCI Loans - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	$ 8,416,126	$ 7,489,763
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	2,111,032	1,959,927
Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	5,771,813	5,053,742
Construction
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	533,281	476,094
Pass
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	8,131,957	7,223,802
Pass | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	2,001,803	1,865,472
Pass | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	5,615,035	4,903,185
Pass | Construction
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	515,119	455,145
Special Mention
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	111,622	92,608
Special Mention | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	63,578	50,453
Special Mention | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	47,022	40,232
Special Mention | Construction
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	1,022	1,923
Substandard
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	170,370	170,809
Substandard | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	45,651	44,002
Substandard | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	109,756	110,325
Substandard | Construction
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	14,963	16,482
Doubtful
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	2,177	2,544
Doubtful | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	0	0
Doubtful | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	0	0
Doubtful | Construction
Accounts, Notes, Loans and Financing Receivable
Total Non-PCI Loans	$ 2,177	$ 2,544