Derivative Financial Instruments - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Derivative [Line Items]
Notional amount	$ 708,000,000		$ 608,000,000
Reclassified interest Income (Expense)	90,993,000	83,478,000
Fixed Interest Swap [Member]
Derivative [Line Items]
Notional amount	38,000,000		38,000,000
Variable Interest Rate Swap [Member]
Derivative [Line Items]
Notional amount	625,000,000		525,000,000
Interest Rate Lock Commitments [Member]
Derivative [Line Items]
Notional amount	62,700,000		19,700,000
Forward Commitments [Member]
Derivative [Line Items]
Notional amount	52,100,000		29,100,000
Customer Derivative Instrument [Member]
Derivative [Line Items]
Notional amount	419,200,000		435,600,000
Offsetting Counter Party Derivative Instrument [Member]
Derivative [Line Items]
Notional amount	419,200,000		435,600,000
Receive Fixed Pay Floating Interest Rate Swaps [Member]
Derivative [Line Items]
Notional amount	45,000,000		45,000,000
Reclassifications out of Accumulated Other Comprehensive Income (Loss) [Member] | Interest Income [Member]
Derivative [Line Items]
Reclassified interest Income (Expense)	600,000
Reclassifications out of Accumulated Other Comprehensive Income (Loss) [Member] | Interest Expense [Member]
Derivative [Line Items]
Reclassified interest Income (Expense)	$ 3,800,000