Derivative Financial Instruments - Summary of Gross Fair Value by Appropriate Balance Sheet Classification (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Assets [Abstract]
Gross Amounts of Recognized Assets	$ 36,645	$ 27,044
Gross Amounts Offset	(8,620)	0
Net Amount presented - Balance Sheet	28,025us-gaap_DerivativeAssets	27,044us-gaap_DerivativeAssets
Liabilities [Abstract]
Gross Amounts of Recognized Liabilities	(9,438)	0
Gross Amounts Offset	8,620	0
Net Amount presented - Balance Sheet	(818)us-gaap_DerivativeLiabilities	0us-gaap_DerivativeLiabilities
Gross Amount of Recognized Assets and Liabilities	27,207	27,044
Gross Amounts Offset	0	0
Net Assets Presented - Balance Sheet	27,207	27,044
Current Asset [Member]
Assets [Abstract]
Gross Amounts of Recognized Assets	27,392	26,202
Gross Amounts Offset	(4,448)	0
Net Amount presented - Balance Sheet	22,944	26,202
Long Term Asset [Member]
Assets [Abstract]
Gross Amounts of Recognized Assets	9,253	842
Gross Amounts Offset	(4,172)	0
Net Amount presented - Balance Sheet	5,081	842
Current Liability [Member]
Liabilities [Abstract]
Gross Amounts of Recognized Liabilities	(2,385)	0
Gross Amounts Offset	2,385	0
Net Amount presented - Balance Sheet	0	0
Gross Amount Deferred premium	(2,063)
Deferred Premium Offset Against Collateral	2,063
Deferred Premium	0
Long Term Liability [Member]
Liabilities [Abstract]
Gross Amounts of Recognized Liabilities	(3,508)	0
Gross Amounts Offset	2,690	0
Net Amount presented - Balance Sheet	(818)	0
Gross Amount Deferred premium	(1,482)
Deferred Premium Offset Against Collateral	1,482
Deferred Premium	$ 0

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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.

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-Publisher FASB

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-Topic 825

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Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

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The net amount as of the balance sheet date of the fair value of derivative assets and derivative liabilities that in accordance with the entity's accounting policy were offset against collateral under a master netting arrangement.

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Fair value, before effects of master netting arrangements, of a financial liability or 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 liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Fair value of the assets less the liabilities of a derivative or group of derivatives.

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