Derivative Financial Instruments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Derivative [Line Items]
Notional amount	$ 441.0	$ 41.0
Fixed Interest Swap [Member]
Derivative [Line Items]
Notional amount	41.0	41.0
Variable Interest Rate Swap [Member]
Derivative [Line Items]
Notional amount	400.0
Interest Rate Lock Commitments [Member]
Derivative [Line Items]
Notional amount	17.9	23.4
Forward Commitments [Member]
Derivative [Line Items]
Notional amount	23.5	32.0
Customer Derivative Instrument [Member]
Derivative [Line Items]
Notional amount	450.0	456.1
Offsetting Counter Party Derivative Instrument [Member]
Derivative [Line Items]
Notional amount	$ 450.0	$ 456.1