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v3.10.0.1

Commitments and Contingencies (Details) - employee | Sep. 29, 2018 | Apr. 13, 2018
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Subsequent Event [Line Items] |  |
Entity number of employees | 2,500 |
Percentage of employees represented by various labor unions | 20.00% |
Percentage Of Employees Covered By CBAs, Or Expired And Under Negotiation | 5.00% |
Cedar Creek |  |
Subsequent Event [Line Items] |  |
Entity number of employees |  | 1,100

X
- Definition Percentage Of Employees Covered By CBAs, Or Expired And Under Negotiation + References No definition available. + Details
Name: | bxc_PercentageOfEmployeesCoveredByCBAsOrExpiredAndUnderNegotiation
Namespace Prefix: | bxc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Percentage of employees represented by various labor unions. + References No definition available. + Details
Name: | bxc_PercentageOfEmployeesRepresentedByVariousLaborUnions
Namespace Prefix: | bxc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of persons employed by the Entity + References No definition available. + Details
Name: | dei_EntityNumberOfEmployees
Namespace Prefix: | dei_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

X
- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
Name: | us-gaap_SubsequentEventLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=bxc_CedarCreekMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |