Stock-based Compensation, Equity Grants, and Warrants - Stock Options Fair Value Assumptions (Details) - Employee Stock Option - $ / shares	3 Months Ended	6 Months Ended
Dec. 31, 2019	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Volatility	50.00%	50.00%
Expected term (Years)	10 years
Stock price threshold term	10 days
October 18, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Strike price (in dollars per share)		$ 4.17
Stock price (in dollars per share)		$ 4.17
Expected term (Years)		10 years
Calculated fair value (in dollars per share)		$ 2.54
October 18, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Strike price (in dollars per share)		4.17
Stock price (in dollars per share)		4.17
Threshold vesting price (in dollars per share)		$ 8.00
Expected term (Years)		10 years
Calculated fair value (in dollars per share)		$ 2.56
October 18, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Strike price (in dollars per share)		4.17
Stock price (in dollars per share)		4.17
Threshold vesting price (in dollars per share)		$ 10.00
Expected term (Years)		10 years
Calculated fair value (in dollars per share)		$ 2.53
October 18, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Strike price (in dollars per share)		4.17
Stock price (in dollars per share)		4.17
Threshold vesting price (in dollars per share)		$ 12.00
Expected term (Years)		10 years
Calculated fair value (in dollars per share)		$ 2.51
Service period		1 year

Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Stock Price Threshold Term

No definition available.

Name:	dlhc_SharebasedCompensationArrangementbySharebasedPaymentAwardFairValueAssumptionsStockPriceThresholdTerm
Namespace Prefix:	dlhc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Threshold Vesting Price

+ References

No definition available.

+ Details

Name:	dlhc_SharebasedCompensationArrangementbySharebasedPaymentAwardFairValueAssumptionsThresholdVestingPrice
Namespace Prefix:	dlhc_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Per share weighted average intrinsic value of equity-based compensation awards vested. Excludes stock and unit options.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodIntrinsicValue
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Agreed-upon price for the exchange of the underlying asset relating to the share-based payment award.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExercisePrice
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

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

- Definition

Price of a single share of a number of saleable stocks of a company.

+ References

No definition available.

+ Details

Name:	us-gaap_SharePrice
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.D.2)
-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_EmployeeStockOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=dlhc_GrantDateOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=dlhc_GrantDateTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=dlhc_GrantDateThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=dlhc_GrantDateFourMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: