Depreciation, Amortization and Accretion - Summary of Depreciation, Amortization and Accretion (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Depreciation, Amortization And Accretion [Abstract]
Depreciation	$ 2,451	$ 2,910	$ 7,278	$ 8,507
Amortization	1,252	1,625	3,749	4,780
Accretion	155	189	460	558
Total depreciation, amortization and accretion	$ 3,858	$ 4,724	$ 11,487	$ 13,845

Amount recognized for the passage of time, typically for liabilities, that have been discounted to their net present values. Excludes accretion associated with asset retirement obligations.

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 420

-SubTopic 10

-Section 35

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6394232&loc=d3e17558-110866

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- Definition

The aggregate amount of recurring noncash expense charged against earnings in the period to allocate the cost of assets over their estimated remaining economic lives.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

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- Definition

The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

+ References

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- Definition

The aggregate net amount of depreciation, amortization, and accretion recognized during an accounting period. As a noncash item, the net amount is added back to net income when calculating cash provided by or used in operations using the indirect method.

+ References

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