XML 29 R29.htm IDEA: XBRL DOCUMENT
v2.4.0.6

ASSET RETIREMENT OBLIGATION: (Tables) | 3 Months Ended
--- | ---
Mar. 31, 2013
ASSET RETIREMENT OBLIGATION: |
Summary of the asset retirement obligation activity | The following table summarizes the asset retirement obligation activity for the three months ended March 31, 2013 and 2012 (in millions):
|  | 2013 |  | 2012 |
Balance as of January 1 |  | $ | 118.2 |  | $ | 62.0 |
Changes in estimates |  | — |  | — |
Additions |  | — |  | — |
Accretion expense |  | 1.8 |  | 0.8 |
Balance as of March 31, |  | $ | 120.0 |  | $ | 62.8 |

X
- Details
Name: | us-gaap_AssetRetirementObligationDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- 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 + Details
Name: | us-gaap_ScheduleOfChangeInAssetRetirementObligationTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration