Derivative Instruments - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Notional amount of swaps	$ 840,190
Fair value of derivatives, in a net liability position	37,545	38,239
Collateral with derivative counterparties, fair value	35,068	37,427
Cash collateral posted	3,472	1,976
Additional amount in excess of posted collateral required in case of breached agreements	2,199	2,224
Swap [Member] | Short [Member]
Derivative [Line Items]
Number of swaps	318
Swap [Member] | Long [Member]
Derivative [Line Items]
Number of swaps	284
Notional amount of swaps	$ 1,040,190