Allowance for Credit Losses - Summary of Activity in Allowance for Loan Losses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 106,709	$ 121,844	$ 113,617	$ 130,200
Loans charged-off	(4,751)	(8,356)	(18,990)	(20,075)
Charged-off loans recovered	6,766	1,320	9,148	3,139
Net (charge-offs) recoveries	2,015	(7,036)	(9,842)	(16,936)
Provision for loan losses	(5,671)	2,636	(722)	4,180
Ending balance	103,053	117,444	103,053	117,444
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	49,932	55,732	51,551	64,370
Loans charged-off	(1,340)	(1,441)	(9,954)	(8,766)
Charged-off loans recovered	4,420	602	4,964	1,940
Net (charge-offs) recoveries	3,080	(839)	(4,990)	(6,826)
Provision for loan losses	(4,591)	(1,161)	1,860	(3,812)
Ending balance	48,421	53,732	48,421	53,732
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	38,382	44,195	42,343	44,069
Loans charged-off	(2,032)	(4,389)	(6,522)	(6,382)
Charged-off loans recovered	1,468	50	2,805	65
Net (charge-offs) recoveries	(564)	(4,339)	(3,717)	(6,317)
Provision for loan losses	(2,551)	3,323	(3,359)	5,427
Ending balance	35,267	43,179	35,267	43,179
Residential Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	6,979	9,331	7,786	9,423
Loans charged-off	(212)	(1,666)	(275)	(2,558)
Charged-off loans recovered	157	68	236	138
Net (charge-offs) recoveries	(55)	(1,598)	(39)	(2,420)
Provision for loan losses	94	788	(729)	1,518
Ending balance	7,018	8,521	7,018	8,521
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	4,107	5,460	4,359	5,542
Loans charged-off	(1,167)	(860)	(2,239)	(2,369)
Charged-off loans recovered	721	600	1,143	996
Net (charge-offs) recoveries	(446)	(260)	(1,096)	(1,373)
Provision for loan losses	1,707	(116)	2,105	915
Ending balance	5,368	5,084	5,368	5,084
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	7,309	7,126	7,578	6,796
Loans charged-off	0	0	0	0
Charged-off loans recovered	0	0	0	0
Net (charge-offs) recoveries	0	0	0	0
Provision for loan losses	(330)	(198)	(599)	132
Ending balance	$ 6,979	$ 6,928	$ 6,979	$ 6,928