Derivative Financial Instruments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Derivative [Line Items]
Notional amount	$ 141.0	$ 41.0
Interest Rate Lock Commitments [Member]
Derivative [Line Items]
Notional amount	26.9	23.4
Forward Commitments [Member]
Derivative [Line Items]
Notional amount	36.1	32.0
Customer Derivative Instrument [Member]
Derivative [Line Items]
Notional amount	449.0	456.1
Offsetting Counter Party Derivative Instrument [Member]
Derivative [Line Items]
Notional amount	449.0	456.1
Fixed Interest Swap [Member]
Derivative [Line Items]
Notional amount	$ 141.0	$ 41.0