Derivative Financial Instruments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Derivative [Line Items]
Notional amount	$ 609.5	$ 464.5
Fixed Interest Swap [Member]
Derivative [Line Items]
Notional amount	39.5	39.5
Variable Interest Rate Swap [Member]
Derivative [Line Items]
Notional amount	525.0	425.0
Interest Rate Lock Commitments [Member]
Derivative [Line Items]
Notional amount	24.5	10.5
Forward Commitments [Member]
Derivative [Line Items]
Notional amount	27.2	17.2
Customer Derivative Instrument [Member]
Derivative [Line Items]
Notional amount	454.7	436.8
Offsetting Counter Party Derivative Instrument [Member]
Derivative [Line Items]
Notional amount	454.7	436.8
Receive Fixed Pay Variable Interest Rate Swaps [Member]
Derivative [Line Items]
Notional amount	$ 45.0