Allowance for Credit Losses and Credit Quality - Schedule of Investment in Impaired Loan (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	$ 32,423		$ 32,773
Unpaid Principal Balance	32,574		33,448
Related Allowance	(151)		(675)
Average Recorded Investment	34,148	43,440
Interest Income Recognized	59	33
Commercial Loans [Member] | With No Related Allowance Recorded [Member] | Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	29,043		26,151
Unpaid Principal Balance	29,043		26,151
Related Allowance
Average Recorded Investment	30,510	32,007
Interest Income Recognized	28
Commercial Loans [Member] | With No Related Allowance Recorded [Member] | Business [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	2,926		1,824
Unpaid Principal Balance	2,926		1,824
Related Allowance
Average Recorded Investment	3,030	6,530
Interest Income Recognized	24
Commercial Loans [Member] | With An Allowance Recorded [Member] | Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	145		3,464
Unpaid Principal Balance	156		3,663
Related Allowance	(11)		(199)
Average Recorded Investment	157	4,657
Interest Income Recognized	2	32
Commercial Loans [Member] | With An Allowance Recorded [Member] | Business [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	309		1,334
Unpaid Principal Balance	449		1,810
Related Allowance	(140)		(476)
Average Recorded Investment	451	246
Interest Income Recognized	5	1
Mortgage Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	9,037		9,861
Unpaid Principal Balance	9,216		10,070
Related Allowance	(179)		(209)
Average Recorded Investment	9,213	5,389
Interest Income Recognized
Mortgage Loans [Member] | With An Allowance Recorded [Member] | Mortgage - Prime [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	9,037		9,861
Unpaid Principal Balance	9,216		10,070
Related Allowance	(179)		(209)
Average Recorded Investment	9,213	5,389
Interest Income Recognized
Mortgage Loans [Member] | With An Allowance Recorded [Member] | Mortgage - Subprime [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment
Unpaid Principal Balance
Related Allowance
Average Recorded Investment
Interest Income Recognized
Consumer Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	9,061		7,445
Unpaid Principal Balance	9,168		7,553
Related Allowance	(107)		(108)
Average Recorded Investment	9,079	8,608
Interest Income Recognized
Consumer Loans [Member] | With An Allowance Recorded [Member] | Indirect Automobile [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	978		865
Unpaid Principal Balance	982		868
Related Allowance	(4)		(3)
Average Recorded Investment	1,267	862
Interest Income Recognized
Consumer Loans [Member] | With An Allowance Recorded [Member] | Credit Card [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	394		413
Unpaid Principal Balance	403		424
Related Allowance	(9)		(11)
Average Recorded Investment	405	423
Interest Income Recognized
Consumer Loans [Member] | With An Allowance Recorded [Member] | Home Equity [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	7,343		5,860
Unpaid Principal Balance	7,434		5,951
Related Allowance	(91)		(91)
Average Recorded Investment	6,910	6,575
Interest Income Recognized
Consumer Loans [Member] | With An Allowance Recorded [Member] | Other [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	346		307
Unpaid Principal Balance	349		310
Related Allowance	(3)		(3)
Average Recorded Investment	497	748
Interest Income Recognized