Summary of Contractual and Notional Amounts of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Home Equity
Financial Instruments [Line Items]
Contractual amounts of financial instrument	$ 259,663	$ 254,603
Commercial and commercial real estate
Financial Instruments [Line Items]
Contractual amounts of financial instrument	20,047	21,972
Residential
Financial Instruments [Line Items]
Contractual amounts of financial instrument	14,398	2,060
Letters of Credit
Financial Instruments [Line Items]
Contractual amounts of financial instrument	1,793	1,178
Other Commitments
Financial Instruments [Line Items]
Contractual amounts of financial instrument	8,035	1,932
Forward commitments to sell residential mortgage loans
Financial Instruments [Line Items]
Notional amount of derivative financial instruments		7,773
Derivative mortgage loan commitments
Financial Instruments [Line Items]
Notional amount of derivative financial instruments		2,356
Customer loan swaps
Financial Instruments [Line Items]
Notional amount of derivative financial instruments	16,222	12,240
Interest rate swaps
Financial Instruments [Line Items]
Notional amount of derivative financial instruments	$ 43,000	$ 43,000