Loans - Risk Category of Loans (Detail) - Non-PCI Loans [Member] - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	$ 8,833,775	$ 7,489,763
Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	2,156,549	1,959,927
Commercial real estate [Member] | Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	6,069,532	5,053,742
Commercial real estate [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	607,694	476,094
Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	8,539,636	7,223,802
Pass [Member] | Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	2,049,752	1,865,472
Pass [Member] | Commercial real estate [Member] | Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	5,893,354	4,903,185
Pass [Member] | Commercial real estate [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	596,530	455,145
Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	148,624	92,608
Special Mention [Member] | Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	68,243	50,453
Special Mention [Member] | Commercial real estate [Member] | Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	79,279	40,232
Special Mention [Member] | Commercial real estate [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	1,102	1,923
Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	143,215	170,809
Substandard [Member] | Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	36,254	44,002
Substandard [Member] | Commercial real estate [Member] | Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	96,899	110,325
Substandard [Member] | Commercial real estate [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	10,062	16,482
Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	2,300	2,544
Doubtful [Member] | Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	2,300	0
Doubtful [Member] | Commercial real estate [Member] | Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	0	0
Doubtful [Member] | Commercial real estate [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	$ 0	$ 2,544