Leases - Other Information Related to Leases (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2024	Sep. 30, 2023
Leases [Abstract]
Cash paid for amounts included in the measurement of lease liabilities	$ 4,572	$ 4,468
New lease liabilities, net of new right-of-use-assets	0	120
Other lease information	$ 4,572	$ 4,588

Operating Lease, Payments, Including New Lease Liabilities, Net of New Right-of-Use Assets

No definition available.

Name:	dlhc_OperatingLeasePaymentsIncludingNewLeaseLiabilitiesNetOfNewRightOfUseAssets
Namespace Prefix:	dlhc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

+ Details

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

- Definition

Amount of cash outflow from operating lease, excluding payments to bring another asset to condition and location necessary for its intended use.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 5
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479041/842-20-45-5

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (g)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-4

+ Details

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

- Definition

Amount of cash outflow from operating lease to bring another asset to condition and location necessary for its intended use.

+ References

+ Details

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