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Employee Benefit Plans (Details) - USD ($) $ in Millions | 12 Months Ended
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Sep. 30, 2023 | Sep. 30, 2022
Retirement Benefits [Abstract] |  |
Defined contribution plan, recorded expense | $ 2.6 | $ 2.2
Defined contribution plan, matching contributions period | 4 years |

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- Definition Represents the vesting period during which the employer contributes a matching contribution to the defined contribution plan. + References No definition available. + Details
Name: | dlhc_DefinedContributionPlanEmployersMatchingContributionVestingPeriod
Namespace Prefix: | dlhc_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_CompensationAndRetirementDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 70 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480794/715-70-50-1 + Details
Name: | us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration