Allowance for Credit Losses - Summary of Activity in Allowance for Loan Losses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 113,617	$ 130,200
Loans charged-off	(14,239)	(11,719)
Charged-off loans recovered	2,382	1,819
Net charge-offs	(11,857)	(9,900)
Provision for loan losses	4,949	1,544
Ending balance	106,709	121,844
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	51,551	64,370
Loans charged-off	(8,614)	(7,325)
Charged-off loans recovered	544	1,338
Net charge-offs	(8,070)	(5,987)
Provision for loan losses	6,451	(2,651)
Ending balance	49,932	55,732
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	42,343	44,069
Loans charged-off	(4,490)	(1,993)
Charged-off loans recovered	1,337	15
Net charge-offs	(3,153)	(1,978)
Provision for loan losses	(808)	2,104
Ending balance	38,382	44,195
Residential Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	7,786	9,423
Loans charged-off	(63)	(892)
Charged-off loans recovered	79	70
Net charge-offs	16	(822)
Provision for loan losses	(823)	730
Ending balance	6,979	9,331
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	4,359	5,542
Loans charged-off	(1,072)	(1,509)
Charged-off loans recovered	422	396
Net charge-offs	(650)	(1,113)
Provision for loan losses	398	1,031
Ending balance	4,107	5,460
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	7,578	6,796
Loans charged-off	0	0
Charged-off loans recovered	0	0
Net charge-offs	0	0
Provision for loan losses	(269)	330
Ending balance	$ 7,309	$ 7,126