Line Of Credit Facility, Additional Borrowing Capacity Under Uncommitted Accordion Feature

No definition available.

Name:	bxc_LineOfCreditFacilityAdditionalBorrowingCapacityUnderUncommittedAccordionFeature
Namespace Prefix:	bxc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line Of Credit Facility, Covenant Terms, Annual Capital Expenditures Limit

+ References

No definition available.

+ Details

Name:	bxc_LineOfCreditFacilityCovenantTermsAnnualCapitalExpendituresLimit
Namespace Prefix:	bxc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Line Of Credit Facility, Covenant Terms, Maximum Portion Of Capital Expenditures Limit, Applicable To Next Fiscal Year

+ References

No definition available.

+ Details

Name:	bxc_LineOfCreditFacilityCovenantTermsMaximumPortionOfCapitalExpendituresLimitApplicableToNextFiscalYear
Namespace Prefix:	bxc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Line Of Credit Facility, Covenant Terms, Minimum Fixed Charge Coverage Ratio

+ References

No definition available.

+ Details

Name:	bxc_LineOfCreditFacilityCovenantTermsMinimumFixedChargeCoverageRatio
Namespace Prefix:	bxc_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Line Of Credit Facility, Covenant Terms, Minimum Fixed Charge Coverage Ratio, Applicable If Certain Conditions Are Met

+ References

No definition available.

+ Details

Name:	bxc_LineOfCreditFacilityCovenantTermsMinimumFixedChargeCoverageRatioApplicableIfCertainConditionsAreMet
Namespace Prefix:	bxc_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Line Of Credit Facility, Covenant Terms, Minimum Remaining Borrowing Capacity Before Fixed Covered Ratio Is Applicable

+ References

No definition available.

+ Details

Name:	bxc_LineOfCreditFacilityCovenantTermsMinimumRemainingBorrowingCapacityBeforeFixedCoveredRatioIsApplicable
Namespace Prefix:	bxc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Line Of Credit Facility, Covenant Terms, Minimum Remaining Borrowing Capacity Level For 60 Days Before Covered Ratio Is Not Applicable

+ References

No definition available.

+ Details

Name:	bxc_LineOfCreditFacilityCovenantTermsMinimumRemainingBorrowingCapacityLevelFor60DaysBeforeCoveredRatioIsNotApplicable
Namespace Prefix:	bxc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Line of Credit Facility, Covenant Terms, Minimum Percentage Of Borrowing Base And Maximum Borrowing Capacity To Apply Fixed Charge Coverage Ratio

+ References

No definition available.

+ Details

Name:	bxc_LineofCreditFacilityCovenantTermsMinimumPercentageOfBorrowingBaseAndMaximumBorrowingCapacityToApplyFixedChargeCoverageRatio
Namespace Prefix:	bxc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The effective interest rate at the end of the reporting period.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_LineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=bxc_WellsFargoBankMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_LetterOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=country_US
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=bxc_TrancheALoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_BaseRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Revolving Credit Facility (Details)	Oct. 09, 2017 USD ($)	Dec. 30, 2017 USD ($)	Aug. 04, 2006 USD ($)
Line of Credit Facility [Line Items]
Minimum remaining borrowing capacity level before covered ratio is applicable	$ 42,500,000
Line of Credit
Line of Credit Facility [Line Items]
Minimum remaining borrowing capacity level before covered ratio is applicable	$ 35,000,000.0
Minimum percentage of maximum borrowing capacity or alternative base before covered ratio is applicable	10.00%
Fixed charge coverage ratio	1.1
Coverage ratio applicable if certain conditions are met	1.0
Capital expenditures limit per fiscal year	$ 30,000,000.0
Unused annual capital expenditures limit that may be used for capital expenditures in the following fiscal year	15,000,000.0
Wells Fargo Bank \| Letter of Credit \| Line of Credit
Line of Credit Facility [Line Items]
Revolving credit facility maximum available credit	335,000,000.0		$ 335,000,000.0
Wells Fargo Bank \| Revolving credit facility \| Line of Credit
Line of Credit Facility [Line Items]
Revolving credit facility maximum available credit			335,000,000.0
Additional borrowing capacity under uncommitted accordion feature	$ 75,000,000.0
Wells Fargo Bank \| Revolving credit facility \| U.S.
Line of Credit Facility [Line Items]
Outstanding lines of credit		$ 182,700,000
Revolving credit facility excess availability		$ 63,300,000
Interest rate on revolving credit facility		4.20%
Tranche A Loan \| Wells Fargo Bank \| Line of Credit
Line of Credit Facility [Line Items]
Debt instrument face amount			$ 16,000,000.0
Minimum \| LIBOR \| Line of Credit
Line of Credit Facility [Line Items]
Credit agreement interest rate	2.25%
Minimum \| Administrative Agent's Base Rate \| Line of Credit
Line of Credit Facility [Line Items]
Credit agreement interest rate	0.75%
Maximum \| LIBOR \| Line of Credit
Line of Credit Facility [Line Items]
Credit agreement interest rate	2.75%
Maximum \| Administrative Agent's Base Rate \| Line of Credit
Line of Credit Facility [Line Items]
Credit agreement interest rate	1.25%