Consolidated Statements of Cash Flows (Parenthetical) $ in Millions	9 Months Ended
Jun. 30, 2016 USD ($)
Non Cash or Part Non Cash Acquisition Non Cash Financial Or Equity Instrument Consideration Shares Issued Value	$ 302
Non Cash or Part Non Cash Acquisition Non Cash Financial Or Equity Instrument Consideration Replacement Awards Value	$ 5

It represents the non cash or part non cash acquisition non cash financial or equity instrument consideration replacement awards value.

No definition available.

Name:	becn_NonCashOrPartNonCashAcquisitionNonCashFinancialOrEquityInstrumentConsiderationReplacementAwardsValue
Namespace Prefix:	becn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration