Derivative Financial Instruments - Offsetting of Derivative Assets (Detail) (Zero cost collars [Member], USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Zero cost collars [Member]
Derivative [Line Items]
Asset Derivatives, Gross amounts of recognized assets/liabilities	$ 8,525	$ 4,912
Asset Derivatives, Gross amounts offset in the balance sheets	0	0
Asset Derivatives, Net amounts of assets/liabilities presented in the balance sheets	8,525	4,912
Asset Derivatives, Gross amounts not offset in the balance sheets, Financial instruments	0	0
Asset Derivatives, Gross amounts not offset in the balance sheets, Cash collateral received/pledged	0	0
Asset Derivatives, Gross amounts not offset in the balance sheets, Net amount	$ 8,525	$ 4,912

Amount of obligation to return cash collateral under master netting arrangements offset against derivative assets.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References

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Amount of obligation to return cash collateral under master netting arrangements that have not been offset against derivative assets.

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Amount of obligation to return securities collateral under master netting arrangements that have not been offset against derivative assets.

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Fair value, after offset of derivative liability, of financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, before offset against an obligation to return collateral under a master netting arrangement. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Fair value, after effects of master netting arrangements, of financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset offset against an obligation to return collateral. Includes assets not subject to a master netting arrangement and not elected to be offset.

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