XML 123 R89.htm IDEA: XBRL DOCUMENT
v3.19.3.a.u2

Income Taxes - Changes in Valuation Allowance (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |
Balance, valuation allowance | $ 552.5 | $ 607.8 | $ 839.1
Remeasurement of deferred tax assets | (41.6) | (32.1) | (205.2)
Release of valuation allowance | 0.0 | 0.0 | 0.0
Expiration of net operating losses | (10.8) | (12.3) | 0.0
Other change in valuation allowance | $ (7.7) | (11.0) | (26.1)
Balance, valuation allowance |  | $ 552.5 | $ 607.8

X
- Definition Valuation Allowance, Deferred Tax Asset, Expiration of Net Operating Losses + References No definition available. + Details
Name: | cenx_ValuationAllowanceDeferredTaxAssetExpirationofNetOperatingLosses
Namespace Prefix: | cenx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Valuation Allowance, Deferred Tax Asset, Release of Valuation Allowance + References No definition available. + Details
Name: | cenx_ValuationAllowanceDeferredTaxAssetReleaseofValuationAllowance
Namespace Prefix: | cenx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Valuation Allowance, Deferred Tax Asset, Remeasurement Due To Tax Cuts & Jobs Act + References No definition available. + Details
Name: | cenx_ValuationAllowanceDeferredTaxAssetRemeasurementDueToTaxCutsJobsAct
Namespace Prefix: | cenx_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
Name: | us-gaap_MovementInValuationAllowancesAndReservesRollForward
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of increase (decrease) in the valuation allowance for a specified deferred tax asset. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 45 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=116821951&loc=d3e32123-109318 + Details
Name: | us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of valuation and qualifying accounts and reserves. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-09) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690 + Details
Name: | us-gaap_ValuationAllowancesAndReservesBalance
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant