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Composition Of Certain Financial Statement Captions (Narrative) (Details) (USD $)
In Thousands, unless otherwise specified
 6 Months Ended
Mar. 27, 2015
Mar. 28, 2014
Sep. 26, 2014
Composition Of Certain Financial Statement Captions [Line Items]      
Capital expenditures incurred, not yet paid $ 27,824us-gaap_CapitalExpendituresIncurredButNotYetPaid $ 2,662us-gaap_CapitalExpendituresIncurredButNotYetPaid  
Raw materials 9,752us-gaap_InventoryRawMaterials   1,013us-gaap_InventoryRawMaterials
Capital expenditures incurred, but not yet paid     8,700dlb_AccrualforUnpaidPropertyPlantandEquipmentAdditions
Other Noncurrent Assets [Member]      
Composition Of Certain Financial Statement Captions [Line Items]      
Raw materials $ 1,800us-gaap_InventoryRawMaterials
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_OtherNoncurrentAssetsMember		   $ 1,700us-gaap_InventoryRawMaterials
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_OtherNoncurrentAssetsMember