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Asset retirement obligations (“ARO”) (Tables)

3 Months Ended

Mar. 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:

	Three months ended March 31, 2015			Year ended December 31, 2014
Beginning balance, ARO liability	$	36,950		$	27,113
Additional ARO liability incurred	1,476			2,548
ARO liabilities settled	(1,298		)	(4,731		)
Accretion expense	74			1,517
ARO liability from Mt. Holly acquisition	—			10,503
Ending balance, ARO liability	$	37,202		$	36,950

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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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