Derivative Financial Instruments (Narrative) (Detail) (USD $)	12 Months Ended		1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Oct. 31, 2007	Dec. 31, 2007	Oct. 31, 2008
Derivative [Line Items]
Deferred accumulated gain		$ 30,600,000
Deferred accumulated after-tax gain		19,900,000
Weighted-average strike rate for outstanding interest rate caps	2.99%
Approximate credit exposure related to swaps with bank customers	39,000,000
Aggregate fair value of securities posted as collateral for derivative contracts	19,300,000
Cash collateral on deposit with other financial institutions	12,100,000
Interest Rate Swaps With Upstream Financial Institution Counterparties [Member]
Derivative [Line Items]
Approximate credit exposure related to swaps with bank customers	8,500,000
Variable-Rate Loans Outstanding [Member]
Derivative [Line Items]
Notional amount of interest rate swap contracts				1,200,000,000
Principal amount outstanding of variable-rate loans			1,200,000,000
Period for which cash flow hedges were used to hedge monthly interest receipts			84 months
Junior Subordinated Deferred Interest Debentures [Member]
Derivative [Line Items]
Notional amount of interest rate swap contracts					$ 120,000,000
Period for which cash flow hedges were used to hedge quarterly interest payments		5 years
Swap fixed interest rate to be paid		5.47%
Variable interest rate of three-month LIBOR plus a margin		1.55%