Loans - Risk Category of Loans (Detail) (Non-PCI Loans [Member], USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	$ 7,720,545	$ 7,489,763
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	2,094,274	1,959,927
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	5,142,588	5,053,742
Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	483,683	476,094
Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	7,421,053	7,223,802
Pass [Member] | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	1,970,835	1,865,472
Pass [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	4,986,138	4,903,185
Pass [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	464,080	455,145
Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	111,677	92,608
Special Mention [Member] | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	67,846	50,453
Special Mention [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	42,198	40,232
Special Mention [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	1,633	1,923
Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	182,199	170,809
Substandard [Member] | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	52,448	44,002
Substandard [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	114,252	110,325
Substandard [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	15,499	16,482
Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	5,616	2,544
Doubtful [Member] | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	3,145	0
Doubtful [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Non-PCI Loans	$ 2,471	$ 2,544