Income Taxes (Reconciliation Of Federal Statutory Tax Rate To Our Effective Tax Rate) (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 26, 2025	Sep. 27, 2024	Sep. 29, 2023	Sep. 30, 2022
Income Tax Disclosure [Abstract]
Federal statutory rate	21.00%	21.00%	21.00%
State income taxes, net of federal effect	0.20%	0.20%	0.30%
Stock-based compensation expense rate			1.20%
Stock-based compensation expense rate	3.50%	1.10%
Research and development tax credits	(5.10%)	(2.70%)	(2.70%)
Tax exempt interest	(1.40%)	(1.30%)	(2.30%)
U.S. tax on foreign entities	1.30%	1.30%	1.30%
Foreign rate differential	(1.20%)	(2.10%)	(1.90%)
Audit settlements	(2.70%)	0.60%	1.90%
Tax Act of 2017	0.00%	(3.20%)	0.00%
Other	(0.10%)	0.50%	0.60%
Effective tax rate	15.50%	15.40%	19.40%
Income tax benefit	$ (46,993)	$ (48,163)	$ (48,409)
Lapse of statute of limitations	19,088	7,318	0
Unrecognized Tax Benefits	83,666	$ 81,615	$ 76,304	$ 69,682
Unrecognized tax benefits if recognized, would affect our effective tax rate	$ 28,100

Effective Income Tax Rate Reconciliation, Federal Tax On Foreign Entities

No definition available.

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Namespace Prefix:	dlb_
Data Type:	dtr-types:percentItemType
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Period Type:	duration

- Definition

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-12

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 231
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482663/740-10-55-231