Fixed Charge Coverage Ratio

No definition available.

Name:	dlhc_FixedChargeCoverageRatio
Namespace Prefix:	dlhc_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Interest Expense Increase (Decrease)

+ References

No definition available.

+ Details

Name:	dlhc_InterestExpenseIncreaseDecrease
Namespace Prefix:	dlhc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Percentage Of Excess Cash Flow For Each Year Of Funded Indebtedness To Adjusted EBITDA

+ References

No definition available.

+ Details

Name:	dlhc_PercentageOfExcessCashFlowForEachYearOfFundedIndebtednessToAdjustedEBITDA
Namespace Prefix:	dlhc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Ratio Of Debt To Earnings Before Interest, Taxes, Depreciation, And Amortization

+ References

No definition available.

+ Details

Name:	dlhc_RatioOfDebtToEarningsBeforeInterestTaxesDepreciationAndAmortization
Namespace Prefix:	dlhc_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Ratio Of Funded Indebtedness To Adjusted Earnings Before Interest, Taxes, Depreciation And Amortization

+ References

No definition available.

+ Details

Name:	dlhc_RatioOfFundedIndebtednessToAdjustedEarningsBeforeInterestTaxesDepreciationAndAmortization
Namespace Prefix:	dlhc_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Voluntary Repayments Of Long-term Debt

+ References

No definition available.

+ Details

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

- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6036836-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateEffectivePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Nominal or face amount used to calculate payments on the derivative asset.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5579245-113959

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5580258-113959

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5579245-113959

+ Details

Name:	us-gaap_DerivativeAssetNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Fixed interest rate related to the interest rate derivative.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeFixedInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04.(a))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e24072-122690

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

+ Details

Name:	us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

Name:	us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in third fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

Name:	us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

Name:	us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in remainder of current fiscal year.

+ References

+ Details

Name:	us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalRemainderOfFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SecuredDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_MediumTermNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dlhc_DebtCovenantAxis=dlhc_ExcessCashFlowsGreaterThanOrEqualto2.50Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dlhc_DebtCovenantAxis=dlhc_ExcessCashFlowsLessThan250Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dlhc_DebtCovenantAxis=dlhc_ExcessCashFlowsEqualto1.50Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dlhc_DebtCovenantAxis=dlhc_ExcessCashFlowsLessThan1.50Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_StandbyLettersOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Credit Facilities - Narrative (Details)	3 Months Ended	6 Months Ended
Credit Facilities - Narrative (Details)	Mar. 31, 2021 USD ($)	Mar. 31, 2021 USD ($)	Sep. 30, 2020 USD ($)
Line of Credit Facility [Line Items]
Debt amortization fiscal year 2021	$ 0	$ 0
Debt amortization fiscal year 2022	6,750,000	6,750,000
Debt amortization fiscal 2023	8,750,000	8,750,000
Debt amortization fiscal 2024	8,750,000	8,750,000
Debt amortization fiscal 2025	38,500,000	38,500,000
Voluntary principal amortization of term debt	3,800,000
Interest Rate Swap
Line of Credit Facility [Line Items]
Derivative notional amount	$ 28,800,000	$ 28,800,000	$ 36,000,000
Derivative fixed interest rate	1.61%	1.61%
Interest expense increase (less than)		$ 200,000
Secured Debt \| Term Loans
Line of Credit Facility [Line Items]
Fixed charge coverage ratio		1.25
Ratio of funded indebtedness to EBITDA through maturity		2.75
Debt amortization fiscal year 2021	$ 7,000,000.0	$ 7,000,000.0
Debt amortization fiscal year 2022	7,000,000.0	7,000,000.0
Debt amortization fiscal 2023	8,750,000	8,750,000
Debt amortization fiscal 2024	8,750,000	8,750,000
Debt amortization fiscal 2025	$ 8,750,000	$ 8,750,000
Secured Debt \| Term Loans \| Excess Cash Flows Greater Than Or Equal to 2.50
Line of Credit Facility [Line Items]
Percentage of excess cash flow for each year of funded indebtedness to EBDTA		75.00%
Ratio of funded indebtedness to adjusted EBDTA, actual		2.50
Secured Debt \| Term Loans \| Excess Cash Flows Less Than 2.50
Line of Credit Facility [Line Items]
Percentage of excess cash flow for each year of funded indebtedness to EBDTA		50.00%
Secured Debt \| Term Loans \| Excess Cash Flows Equal to 1.50
Line of Credit Facility [Line Items]
Ratio of funded indebtedness to adjusted EBDTA, actual		1.5
Secured Debt \| Term Loans \| Excess Cash Flows Less Than 1.50
Line of Credit Facility [Line Items]
Percentage of excess cash flow for each year of funded indebtedness to EBDTA		0.00%
Ratio of funded indebtedness to adjusted EBDTA, actual		1.5
Secured Debt \| Term Loans \| Maximum
Line of Credit Facility [Line Items]
Ratio of funded indebtedness to EBITDA through maturity		3.75
Interest rate spread	4.50%	4.50%
Secured Debt \| Term Loans \| Maximum \| Excess Cash Flows Less Than 2.50
Line of Credit Facility [Line Items]
Ratio of funded indebtedness to adjusted EBDTA, actual		2.50
Secured Debt \| Term Loans \| Minimum
Line of Credit Facility [Line Items]
Interest rate spread	2.50%	2.50%
Secured Debt \| Term Loans \| LIBOR
Line of Credit Facility [Line Items]
Interest rate spread	0.12%	0.12%
Secured Debt \| Revolving Line of Credit
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity	$ 25,000,000.0	$ 25,000,000.0
Line of credit outstanding balance	0	0
Line of credit, current borrowing capacity	$ 25,000,000.0	$ 25,000,000.0
Secured Debt \| Revolving Line of Credit \| LIBOR
Line of Credit Facility [Line Items]
Interest rate spread	0.12%	0.12%
Secured Debt \| Letter of Credit
Line of Credit Facility [Line Items]
Line of credit, current borrowing capacity	$ 5,000,000	$ 5,000,000