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Asset retirement obligations ('ARO') (Tables)

12 Months Ended

Dec. 31, 2015

Asset Retirement Obligation Disclosure [Abstract]

Schedule of changes in asset retirement obligations

The reconciliation of the changes in the asset retirement obligations is presented below:

	Year ended December 31,
	2015			2014
Beginning balance, ARO liability	$	36,950		$	27,113
Additional ARO liability incurred	3,797			2,548
ARO liabilities settled	(5,514		)	(4,731		)
Accretion expense	1,818			1,517
Adjustments	(1,886		)	—
ARO liability from Mt. Holly acquisition	—			10,503
Ending balance, ARO liability	$	35,165		$	36,950

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- References

No definition available.

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- Definition

Tabular disclosure of the changes in carrying amount of a liability for asset retirement obligations, for changes such as new obligations, changes in estimates of existing obligations, spending on existing obligations, property dispositions, and foreign currency translation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13201-110859

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