Commitments And Contingencies (Narrative) (Details)	6 Months Ended
Mar. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Term of agreement	20 years

Unrecorded Unconditional Obligation, Term of Agreement

No definition available.

Name:	dlb_UnrecordedUnconditionalObligationTermOfAgreement
Namespace Prefix:	dlb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration