Derivatives - Fair Values of Derivative Instruments on Balance Sheet (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Derivatives designated as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Derivatives designated as hedging instruments, Fair Value, Gross Assets
Derivatives designated as hedging instruments, Fair Value, Gross Liability	298	107
Derivatives not designated as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Derivatives designated as hedging instruments, Fair Value, Gross Assets	20,093	14,952
Derivatives designated as hedging instruments, Fair Value, Gross Liability	20,802	15,536
Other liabilities [Member] | Derivatives designated as hedging instruments [Member] | Interest rate contracts [Member]
Derivatives, Fair Value [Line Items]
Derivatives designated as hedging instruments, Fair Value, Gross Liability	298	107
Other liabilities [Member] | Derivatives not designated as hedging instruments [Member] | Interest rate contracts [Member]
Derivatives, Fair Value [Line Items]
Derivatives designated as hedging instruments, Fair Value, Gross Liability	20,802	15,536
Other assets [Member] | Derivatives designated as hedging instruments [Member] | Interest rate contracts [Member]
Derivatives, Fair Value [Line Items]
Derivatives designated as hedging instruments, Fair Value, Gross Assets
Other assets [Member] | Derivatives not designated as hedging instruments [Member] | Interest rate contracts [Member]
Derivatives, Fair Value [Line Items]
Derivatives designated as hedging instruments, Fair Value, Gross Assets	$ 20,093	$ 14,952