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Income Taxes - Deferred Tax Asset Valuation Allowance Activity (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 30, 2017 | Dec. 29, 2018 | Dec. 30, 2017
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] |  |  |
Balance as of beginning of the year |  | $ 10,415 | $ 97,552
Valuation allowance provided for taxes related to: |  |  |
Loss (income) before income taxes |  | 1,933 | (4,300)
Tax Cuts and Jobs Act of 2017 |  | 0 | (29,387)
Release of valuation allowance | $ (53,500) | 0 | (53,450)
Balance as of end of the year | $ 10,415 | $ 12,348 | $ 10,415

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- Definition Effective Income Tax Rate Reconciliation, Tax Cuts and Jobs Act of 2017, Valuation Allowance + References No definition available. + Details
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Namespace Prefix: | bxc_
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Balance Type: | credit
Period Type: | duration

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- Definition This element represent represents valuation allowance provided for taxes related to loss before income tax. + References No definition available. + Details
Name: | bxc_ValuationAllowancesProvidedForTaxesRelatedToIncomeBeforeIncomeTaxes
Namespace Prefix: | bxc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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- Definition Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319 + Details
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- 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
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
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- 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=84176650&loc=d3e32123-109318 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
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