Derivative Financial Instruments - Schedule of Notional Amounts and Estimated Fair Values of Interest Rate Derivative Contracts Outstanding (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Designated as Hedging Instrument [Member] | Financial Institution Counterparties Loan Lease Interest Rate Swaps Assets [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	$ 23,884	$ 14,748
Estimated Fair Value	103	24
Designated as Hedging Instrument [Member] | Financial Institution Counterparties Loan Lease Interest Rate Swaps Liabilities [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	84,404	84,577	67,517
Estimated Fair Value	(6,565)	(7,186)	(7,736)
Designated as Hedging Instrument [Member] | Interest Rate Swap On Junior Subordinated Deferrable Interest Debentures [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	120,000	120,000	120,000
Estimated Fair Value	(3,306)	(4,365)	(7,205)
Non Designated as Hedging Instrument [Member] | Financial Institution Counterparties Loan Lease Interest Rate Swaps Assets [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	50,915
Estimated Fair Value	147
Non Designated as Hedging Instrument [Member] | Financial Institution Counterparties Loan Lease Interest Rate Swaps Liabilities [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	741,344	797,311	637,356
Estimated Fair Value	(54,434)	(60,994)	(57,314)
Non Designated as Hedging Instrument [Member] | Financial Institution Counterparties Loan Lease Interest Rate Caps Assets [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	33,058	30,000	20,000
Estimated Fair Value	12	12	28
Non Designated as Hedging Instrument [Member] | Customer Counterparties Loan Lease Interest Rate Swaps Assets [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	741,344	797,311	637,356
Estimated Fair Value	54,312	60,854	57,105
Non Designated as Hedging Instrument [Member] | Customer Counterparties Loan Lease Interest Rate Swaps Liabilities [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	50,915
Estimated Fair Value	(147)
Non Designated as Hedging Instrument [Member] | Customer Counterparties Loan Lease Interest Rate Caps Liabilities [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	33,058	30,000	20,000
Estimated Fair Value	$ (12)	$ (12)	$ (28)