Long-Lived Assets - Changes in Asset Retirement Obligation Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Asset Retirement Obligation Liabilities [Line Items]
Balance	$ 7,957us-gaap_AssetRetirementObligation	$ 7,936us-gaap_AssetRetirementObligation
Accretion	755	567
Amounts paid	(399)	(415)
Reductions recorded	(1,166)	(131)
Reclassifications	0	0
Balance	7,147us-gaap_AssetRetirementObligation	7,957us-gaap_AssetRetirementObligation
Short-Term Portion [Member]
Asset Retirement Obligation Liabilities [Line Items]
Balance	358	379
Accretion	28	(112)
Amounts paid	(399)	(415)
Reductions recorded	(141)	(445)
Reclassifications	496	951
Balance	342	358
Long-Term Portion [Member]
Asset Retirement Obligation Liabilities [Line Items]
Balance	7,599	7,557
Accretion	727	679
Amounts paid	0	0
Reductions recorded	(1,025)	314
Reclassifications	(496)	(951)
Balance	$ 6,805	$ 7,599

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The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Asset Retirement Obligation

-URI http://asc.fasb.org/extlink&oid=6505190

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- Definition

Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6392676&loc=d3e7480-110848

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)(3)

-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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- Definition

Amount of cash paid during the period to settle an asset retirement obligation. Amounts paid to settle an asset retirement obligation are generally included in the operating section of the Statement of Cash Flows.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 17

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3367-108585

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- Definition

Net Increase or Decrease in the asset retirement obligation during the period.

+ References

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Amount of the Increase or Decrease in the amount of the asset retirement obligation during the current period for changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation.

+ References

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