Derivatives - Offsetting Derivative Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Gross Amounts of Recognized Assets	$ 15,253	$ 19,448
Gross Amounts Offset in the Statement of Financial Position
Net Amounts of Assets Presented in the Statement of Financial Position	15,253	19,448
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, Assets	1,949
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received, Assets
Net Amount, Assets	13,304	19,448
Gross Amounts of Recognized Liabilities	15,082	20,455
Gross Amounts Offset in the Statement of Financial Position
Net Amounts of Liabilities Presented in the Statement of Financial Position	15,082	20,455
Gross Amounts Not Offset in the Statement of Financial Position, Financial Instruments, Liability	1,949
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Pledged, Liability	9,113	16,839
Net Amount, Liability	$ 4,020	$ 3,616