Number of Loans and Leases Modified in TDRs and Total Recorded Investments and Unpaid Principal Balances (Detail) (Class of Financing Receivable, USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012 Contract	Sep. 30, 2011 Contract	Sep. 30, 2012 Contract	Sep. 30, 2011 Contract
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	24	33	95	133
Recorded Investment	$ 4,700,000	$ 23,100,000	$ 41,200,000	$ 70,000,000
Unpaid Principal Balance	5,300,000	27,800,000	46,800,000	84,000,000
Commercial
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	1	8	10	19
Recorded Investment	2,700,000	16,000,000	30,300,000	48,000,000
Unpaid Principal Balance	2,700,000	18,700,000	32,500,000	56,100,000
Commercial | Commercial Real Estate Portfolio Segment
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	1	6	7	14
Recorded Investment	2,700,000	10,600,000	24,600,000	39,400,000
Unpaid Principal Balance	2,700,000	12,300,000	26,200,000	46,000,000
Commercial | Lease Financing, net
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases			1
Recorded Investment			5,200,000
Unpaid Principal Balance			5,200,000
Commercial | Commercial and Institutional
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases		2	2	5
Recorded Investment		5,400,000	500,000	8,600,000
Unpaid Principal Balance		6,400,000	1,100,000	10,100,000
Personal
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	23	25	85	114
Recorded Investment	2,000,000	7,100,000	10,900,000	22,000,000
Unpaid Principal Balance	2,600,000	9,100,000	14,300,000	27,900,000
Personal | Residential Real Estate
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	23	25	84	113
Recorded Investment	2,000,000	7,100,000	10,100,000	22,000,000
Unpaid Principal Balance	2,600,000	9,100,000	13,500,000	27,900,000
Personal | Private Client
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases			1	1
Recorded Investment			800,000
Unpaid Principal Balance			$ 800,000