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, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 121,844	$ 132,870	$ 130,200	$ 133,802
Loans charged-off	(8,356)	(12,383)	(20,075)	(20,929)
Charged-off loans recovered	1,320	1,938	3,139	4,178
Net charge-offs	(7,036)	(10,445)	(16,936)	(16,751)
Provision for loan losses	2,636	7,429	4,180	12,803
Ending balance	117,444	129,854	117,444	129,854
Commercial and industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	55,732	73,311	64,370	73,649
Loans charged-off	(1,441)	(5,406)	(8,766)	(10,213)
Charged-off loans recovered	602	1,304	1,940	2,309
Net charge-offs	(839)	(4,102)	(6,826)	(7,904)
Provision for loan losses	(1,161)	1,313	(3,812)	4,777
Ending balance	53,732	70,522	53,732	70,522
Commercial real estate loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	44,195	34,415	44,069	34,637
Loans charged-off	(4,389)	(5,379)	(6,382)	(6,459)
Charged-off loans recovered	50	116	65	236
Net charge-offs	(4,339)	(5,263)	(6,317)	(6,223)
Provision for loan losses	3,323	6,406	5,427	7,144
Ending balance	43,179	35,558	43,179	35,558
Residential mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	9,331	9,837	9,423	9,120
Loans charged-off	(1,666)	(583)	(2,558)	(1,759)
Charged-off loans recovered	68	111	138	625
Net charge-offs	(1,598)	(472)	(2,420)	(1,134)
Provision for loan losses	788	1,375	1,518	2,754
Ending balance	8,521	10,740	8,521	10,740
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	5,460	7,940	5,542	8,677
Loans charged-off	(860)	(1,015)	(2,369)	(2,498)
Charged-off loans recovered	600	407	996	1,008
Net charge-offs	(260)	(608)	(1,373)	(1,490)
Provision for loan losses	(116)	(1,523)	915	(1,378)
Ending balance	5,084	5,809	5,084	5,809
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	7,126	7,367	6,796	7,719
Provision for loan losses	(198)	(142)	132	(494)
Ending balance	$ 6,928	$ 7,225	$ 6,928	$ 7,225