Derivative Instruments and Other Hedging Activities - Schedule of Outstanding Derivative Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Derivative Instruments And Hedging Activities [Line Items]
Derivative Asset, Fair Value	$ 34,504	$ 35,202
Derivative Liability, Fair Value	22,649	27,783
Designated As Hedging Instruments [Member]
Derivative Instruments And Hedging Activities [Line Items]
Derivative Asset, Notional Amount	35,000	35,000
Derivative Liability, Notional Amount	35,000	35,000
Not Designated As Hedging Instruments [Member]
Derivative Instruments And Hedging Activities [Line Items]
Derivative Asset, Notional Amount	862,005	975,357
Derivative Liability, Notional Amount	672,664	613,690
Other Assets [Member] | Designated As Hedging Instruments [Member]
Derivative Instruments And Hedging Activities [Line Items]
Derivative Asset, Fair Value	1,744	499
Other Assets [Member] | Not Designated As Hedging Instruments [Member]
Derivative Instruments And Hedging Activities [Line Items]
Derivative Asset, Fair Value	39,464	41,620
Other Liabilities [Member] | Designated As Hedging Instruments [Member]
Derivative Instruments And Hedging Activities [Line Items]
Derivative Liability, Fair Value	590	1,843
Other Liabilities [Member] | Not Designated As Hedging Instruments [Member]
Derivative Instruments And Hedging Activities [Line Items]
Derivative Liability, Fair Value	33,582	35,047
Interest Rate Contracts [Member] | Designated As Hedging Instruments [Member]
Derivative Instruments And Hedging Activities [Line Items]
Derivative Asset, Notional Amount	35,000	35,000
Derivative Liability, Notional Amount	35,000	35,000
Interest Rate Contracts [Member] | Not Designated As Hedging Instruments [Member]
Derivative Instruments And Hedging Activities [Line Items]
Derivative Asset, Notional Amount	361,679	374,536
Derivative Liability, Notional Amount	361,679	374,536
Interest Rate Contracts [Member] | Other Assets [Member] | Designated As Hedging Instruments [Member]
Derivative Instruments And Hedging Activities [Line Items]
Derivative Asset, Fair Value	1,744	499
Interest Rate Contracts [Member] | Other Assets [Member] | Not Designated As Hedging Instruments [Member]
Derivative Instruments And Hedging Activities [Line Items]
Derivative Asset, Fair Value	22,058	25,940
Interest Rate Contracts [Member] | Other Liabilities [Member] | Designated As Hedging Instruments [Member]
Derivative Instruments And Hedging Activities [Line Items]
Derivative Liability, Fair Value	590	1,843
Interest Rate Contracts [Member] | Other Liabilities [Member] | Not Designated As Hedging Instruments [Member]
Derivative Instruments And Hedging Activities [Line Items]
Derivative Liability, Fair Value	22,059	25,940
Forward Sale Contracts [Member] | Not Designated As Hedging Instruments [Member]
Derivative Instruments And Hedging Activities [Line Items]
Derivative Asset, Notional Amount	66,247	212,028
Derivative Liability, Notional Amount	116,609	53,269
Forward Sale Contracts [Member] | Other Assets [Member] | Not Designated As Hedging Instruments [Member]
Derivative Instruments And Hedging Activities [Line Items]
Derivative Asset, Fair Value	593	2,774
Forward Sale Contracts [Member] | Other Liabilities [Member] | Not Designated As Hedging Instruments [Member]
Derivative Instruments And Hedging Activities [Line Items]
Derivative Liability, Fair Value	774	343
Written And Purchased Options [Member] | Not Designated As Hedging Instruments [Member]
Derivative Instruments And Hedging Activities [Line Items]
Derivative Asset, Notional Amount	434,079	388,793
Derivative Liability, Notional Amount	194,376	185,885
Written And Purchased Options [Member] | Other Assets [Member] | Not Designated As Hedging Instruments [Member]
Derivative Instruments And Hedging Activities [Line Items]
Derivative Asset, Fair Value	16,813	12,906
Written And Purchased Options [Member] | Other Liabilities [Member] | Not Designated As Hedging Instruments [Member]
Derivative Instruments And Hedging Activities [Line Items]
Derivative Liability, Fair Value	$ 10,749	$ 8,764