| **Business Overview (Details)**                                                                   | 3 Months Ended | 9 Months Ended | 12 Months Ended |
|---------------------------------------------------------------------------------------------------|----------------|----------------|-----------------|
||
| **Concentration Risk [Line Items]**                                                               |           |           |            |
| Minimum period for which entity has provided professional services to the U.S. Government (years) |           |           | 25 years        |
| Number of employees (employee)                                                                    |           |           | 1,200           |
| Minimum number of locations in which entity operates (location)                                   |           |           | 25              |
| Number of broad integrated revenue streams                                                        |           |           | 2               |
| US Government [Member] | Revenue concentration | Customer concentration                           |           |           |            |
| **Concentration Risk [Line Items]**                                                               |           |           |            |
| Concentration risk percentage (percent)                                                           |           |           | 100.00%         |
| DVA | Revenue concentration | Customer concentration                                              |           |           |            |
| **Concentration Risk [Line Items]**                                                               |           |           |            |
| Concentration risk percentage (percent)                                                           | 96.00%         | 97.00%         | 96.00%          |
| DVA | Minimum                                                                                     |           |           |            |
| **Concentration Risk [Line Items]**                                                               |           |           |            |
| Term of government contract                                                                       |           |           | 2 years         |
| DVA | Maximum                                                                                     |           |           |            |
| **Concentration Risk [Line Items]**                                                               |           |           |            |
| Term of government contract                                                                       |           |           | 4 years         |

| X                                                                                                                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Number of persons employed by the Entity
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Represents the number of integrated revenue streams areas of the entity.
+ References
No definition available.
+ Details**Name:**dlhc_EntityNumberofIntegratedRevenueStreams**Namespace Prefix:**dlhc_**Data Type:**xbrli:integerItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                              |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Represents the period for which the entity has provided professional services to U.S. Government.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Represents the term of the award granted to the entity.
+ References
No definition available.
+ Details**Name:**dlhc_GovernmentContractTermofAward**Namespace Prefix:**dlhc_**Data Type:**xbrli:durationItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                              |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Represents the minimum number of locations the entity operates in as of the balance sheet date.
+ References
No definition available.
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| X                                                                                                                                                              |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_ConcentrationRiskLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.
+ References
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