Derivative Instruments - Offsetting of Derivative Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Derivatives, Fair Value [Line Items]
Gross Amount	$ 38,655	$ 43,369
Gross Amounts Offset in the Balance Sheet, Derivative Liabilities
Net Amount Presented in the Balance Sheet	38,655	43,369
Derivative Liabilities Subject to Master Netting Arrangement [Member]
Derivatives, Fair Value [Line Items]
Net Amount Presented in the Balance Sheet	37,565	40,323
Derivative Liabilities Subject to Master Netting Arrangement [Member] | Interest Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Amount	37,565	40,323
Gross Amounts Offset in the Balance Sheet, Derivative Liabilities
Net Amount Presented in the Balance Sheet	37,565	40,323
Derivative Liabilities Not Subject to Master Netting Arrangement [Member] | Interest Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Amount	1,040	3,014
Gross Amounts Offset in the Balance Sheet, Derivative Liabilities
Net Amount Presented in the Balance Sheet	1,040	3,014
Derivative Liabilities Not Subject to Master Netting Arrangement [Member] | Equity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Amount	50	32
Gross Amounts Offset in the Balance Sheet, Derivative Liabilities
Net Amount Presented in the Balance Sheet	$ 50	$ 32