New Accounting Pronouncements	12 Months Ended
	Sep. 30, 2023
Accounting Changes and Error Corrections [Abstract]
New Accounting Pronouncements	New Accounting Pronouncements In March 2020 and January 2021, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2020-04, "Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting” and ASU No. 2021-01, “Reference Rate Reform (Topic 848): Scope,” respectively (collectively, “Topic 848”). Topic 848 provides optional expedients and exceptions for applying GAAP to contracts, hedging relationships and other transactions that reference the London Interbank Offered Rate (“LIBOR”) or another reference rate expected to be discontinued because of reference rate reform. In December 2022, FASB issued ASU 2022-06 "Reference Rate Reform (Topic 848): Deferral of the Sunset Date of Topic 848" which defers the end date for electing the relief provided in Topic 848 from December 31, 2022 to December 31, 2024. In the first quarter of fiscal 2023, the Company adopted the optional expedients and exceptions provided in Topic 848. The adoption did not have a material impact on the Company’s consolidated financial statements. DLH adopted the standard in fiscal year 2023 by virtue of the loan modification on December 8, 2022 that converted the basis of the interest rate from LIBOR to Secured Overnight Financing Rate ("SOFR"). DLH had no other contracts or offerings that used LIBOR as a basis for rates.