Date when the acquirer obtains control of the acquiree, in CCYY-MM-DD format.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 25

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=34752592&loc=d3e845-128460

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Acquisition Date

-URI http://asc.fasb.org/extlink&oid=6919109

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 25

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=34752592&loc=d3e848-128460

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463

+ Details

Name:	us-gaap_BusinessAcquisitionEffectiveDateOfAcquisition1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Definition

The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(2)-(3)

-URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463

+ Details

Name:	us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period.

+ References

+ Details

Name:	us-gaap_BusinessAcquisitionsProFormaRevenue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

Reference 2: 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=34725769&loc=d3e28878-108400

+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 2: 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(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Details

Name:	us-gaap_BusinessAcquisitionAxis=ck0001571371_TwoThousandFourteenAcquisitionFiveMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=ck0001571371_TwoThousandFourteenAcquisitionFourMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=ck0001571371_TwoThousandFourteenAcquisitionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=ck0001571371_TwoThousandFourteenAcquisitionOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=ck0001571371_TwoThousandFourteenAcquisitionThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=ck0001571371_TwoThousandFourteenAcquisitionTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=ck0001571371_TwoThousandThirteenAcquisitionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=ck0001571371_TwoThousandTwelveAcquisitionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=ck0001571371_WestMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Acquisitions - Additional Information (Detail) (USD $)	12 Months Ended			9 Months Ended
Acquisitions - Additional Information (Detail) (USD $)	Dec. 27, 2014	Dec. 28, 2013	Dec. 29, 2012	Sep. 27, 2014	Sep. 08, 2014	Jan. 17, 2014	Jan. 31, 2012
Business Acquisition [Line Items]
Proforma effect on revenue	$ 1,326,861,000	$ 1,230,491,000	$ 1,022,535,000
Net income from the acquisition	8,181,000	(104,705,000)	(46,405,000)
Senior Notes [Member]
Business Acquisition [Line Items]
Debt instrument, face amount	625,000,000	250,000,000			115,000,000	260,000,000	250,000,000
Interest rate							10.50%
West Region [Member] \| Senior Notes [Member]
Business Acquisition [Line Items]
Debt instrument, face amount						260,000,000
Interest rate						10.50%
2014 Acquisitions [Member] \| West Region [Member]
Business Acquisition [Line Items]
Business acquisition date	Mar. 31, 2014
2014 Acquisitions [Member] \| Central Region [Member]
Business Acquisition [Line Items]
Business acquisition date	Oct. 03, 2014
2014 Acquisitions [Member] \| West Region [Member]
Business Acquisition [Line Items]
Business acquisition date	Jan. 17, 2014
2014 Acquisitions [Member] \| West Region [Member]
Business Acquisition [Line Items]
Business acquisition date	Sep. 30, 2014
2014 Acquisitions [Member] \| East Region [Member]
Business Acquisition [Line Items]
Business acquisition date	Jun. 09, 2014
2014 Acquisitions [Member]
Business Acquisition [Line Items]
Proforma effect on revenue		305,700,000	82,400,000
Net income from the acquisition		33,700,000	4,700,000
2014 Acquisitions [Member] \| West Region [Member]
Business Acquisition [Line Items]
Business acquisition date	Sep. 19, 2014
2014 Acquisitions [Member] \| West Region [Member]
Business Acquisition [Line Items]
Business acquisition date	Sep. 04, 2014
2014 Acquisitions [Member] \| West Region [Member] \| Senior Notes [Member]
Business Acquisition [Line Items]
Debt instrument, face amount	115,000,000
Interest rate	10.50%
2014 Acquisitions [Member] \| West Region [Member]
Business Acquisition [Line Items]
Business acquisition date	Jul. 29, 2014
2013 Acquisitions [Member]
Business Acquisition [Line Items]
Proforma effect on revenue		8,600,000	13,800,000
Net income from the acquisition		(3,400,000)	(500,000)
2013 Acquisitions [Member] \| West Region [Member]
Business Acquisition [Line Items]
Business acquisition date				Apr. 01, 2013
2013 Acquisitions [Member] \| Central Region [Member]
Business Acquisition [Line Items]
Business acquisition date	Apr. 01, 2013
2012 Acquisitions [Member]
Business Acquisition [Line Items]
Proforma effect on revenue	197,500,000
Net income from the acquisition	35,600,000
2012 Acquisitions [Member] \| Alleyton, Southwest Ready Mix [Member]
Business Acquisition [Line Items]
Proforma effect on revenue	150,900,000
2012 Acquisitions [Member] \| Colorado County S&G [Member]
Business Acquisition [Line Items]
Net income from the acquisition	$ 32,600,000
2012 Acquisitions [Member] \| West Region [Member]
Business Acquisition [Line Items]
Business acquisition date	Nov. 30, 2012
2012 Acquisitions [Member] \| East Region [Member]
Business Acquisition [Line Items]
Business acquisition date	Oct. 05, 2012
2012 Acquisitions [Member] \| Central Region [Member]
Business Acquisition [Line Items]
Business acquisition date	Feb. 29, 2012