Derivative Instruments - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013 Agreement	Dec. 31, 2012
Derivative [Line Items]
Number of separate interest rate derivative agreements	4
Notional amount of swaps	$ 828,576
Fair value of derivatives, in a net liability position	38,239	59,341
Collateral with derivative counterparties, fair value	37,427	60,062
Cash collateral posted	1,976
Additional amount in excess of posted collateral required in case of breached agreements	2,224	2,428
Swap [Member] | Short [Member]
Derivative [Line Items]
Number of swaps	312
Swap [Member] | Long [Member]
Derivative [Line Items]
Number of swaps	278
Notional amount of swaps	$ 1,028,576