Significant Accounting Policies (Policies)	3 Months Ended
Significant Accounting Policies (Policies)	Dec. 31, 2019
Accounting Policies [Abstract]
New Accounting Pronouncements and Adoption of New Accounting Standards	New Accounting Pronouncements In February 2016, the FASB issued an Accounting Standard Update ("ASU") 2016-02, Leases (Topic 842), to improve financial reporting about leasing transactions. This account standard requires organizations that lease assets, referred to as "Lessees", to recognize on the balance sheet right-of-use assets and lease liabilities. Per the ASU, we determine if a contract contains a lease by identifying an asset and determining if we have the right to control the use of the identified asset for a period of time in exchange for consideration. A contract conveys the right to control the use of an identified asset when the lessee has the right to direct the use of the identified asset and obtain substantially all economic benefits from its use throughout the period of its use. We also determine if a lease qualifies as an operating or finance lease. All Company leases at standard adoption were operating leases. The standards also require lessees to identify and separate lease and non-lease components. The Company elected not to separate lease and non-lease components per the practical expedient provided in ASU 2018-11. Upon lease commencement, the lease liability and right-of-use asset are recorded on the balance sheet. The lease liability is measured as the present value of future minimum lease payments to be made during the lease term. The right-of-use asset is measured as the present value of future minimum lease payments to be made during the lease term, plus lease payments made to the lessor before or at commencement and indirect costs paid less lease incentives received. DLH adopted this standard on October 1, 2019 and recognized initial right-of use assets and lease liabilities of $17.4 million and $18.0 million, respectively. At adoption, the Company elected several practical expediencies to facilitate the implementation of the new standard. As such we did not reassess and include initial direct costs in the measurement of right-of-use assets, capitalize leases with terms of 12 months or less, nor reassess lease classification of existing leases. In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses, which requires companies to record an allowance for expected credit losses over the contractual term of certain financial assets, including short-term trade receivables and contract assets. Additionally, it expands disclosure requirements for credit quality of financial assets. ASU 2016-13 becomes effective for the Company in the first quarter of fiscal year 2021. We do not expect a material impact to our operating results, financial position or cash flows as a result of adopting this new standard. In January 2017, the FASB issued ASU 2017-04, Simplifying the Test for Goodwill Impairment, which simplifies the accounting for goodwill impairments by eliminating step two from the goodwill impairment test. Instead, if the carrying amount of a reporting unit exceeds its fair value, an impairment loss shall be recognized in an amount equal to that excess, limited to the total amount of goodwill allocated to that reporting unit. ASU 2017-04 also clarifies that an entity should consider income tax effects from any tax-deductible goodwill on the carrying amount of the reporting unit when measuring the goodwill impairment loss, if applicable. The new standard is effective for fiscal years beginning after December 15, 2019 for both interim and annual reporting periods. The Company has adopted this stand in the first quarter of fiscal 2020 and adoption did not have an impact on the Company's consolidated financial statements
Revenue Recognition	Revenue Recognition We account for a contract when both we and the customer approve and commit; our rights and those of the customer are identified, payment terms are identified; the contract has commercial substance; and collectability of consideration is probable. At contract inception, we identify the distinct goods or services promised in the contract, referred to as performance obligations. Then we determine the total transaction price for the contract; which is the total consideration which we can expect in exchange for the promised goods or services in the contract. The transaction price may include fixed or variable amounts. Due to our contracts being predominantly time and material, the Company does not have variable consideration. The transaction price is allocated to each distinct performance obligation using our best estimate of the standalone selling price for each service promised in the contract. The primary method used to estimate standalone selling price is the hourly billing rate for each labor category identified in the contract with the customer. Revenue is recognized when, or as, the performance obligation is satisfied. We recognize revenue over time when there is a continuous transfer of control to our customer. For our U.S. government contracts, this continuous transfer of control to the customer is supported by clauses in the contract that allow the U.S. government to unilaterally terminate the contract for convenience, pay us for costs incurred plus a reasonable profit and take control of any work in process. When control is transferred over time, revenue is recognized based on the extent of progress towards completion of the performance obligation. For services contracts, we satisfy our performance obligations as services are rendered. We use a cost-based input method to measure progress. Contract costs include labor, material and allocable indirect expenses. For time-and-material contracts, we bill the customer per labor hour and per material, and revenue is recognized in the amount invoiced since the amount corresponds directly to the value of our performance to date. We consider control to transfer when we have a present right to payment. Essentially, all of our contracts satisfy their performance obligations over time. Contracts are often modified to account for changes in contract specifications and requirements. Contract modifications impact performance obligations when the modification either creates new or changes the existing enforceable rights and obligations. The effect of a contract modification on the transaction price and our measure of progress for the performance obligation to which it relates is recognized as an adjustment to revenue and profit cumulatively. Furthermore, a significant change in one or more estimates could affect the profitability of our contracts. We recognize adjustments in estimated profit on contracts in the period identified. For time-and-materials contracts, revenue is recognized to the extent of billable rates times hours delivered plus materials and other reimbursable costs incurred. Revenue for cost-reimbursable contracts is recorded as reimbursable costs are incurred, including an estimated share of the applicable contractual fees earned. Contract costs are expensed as incurred. Estimated losses are recognized when identified. Contract assets - Amounts are invoiced as work progresses in accordance with agreed-upon contractual terms. In part, revenue recognition occurs before we have the right to bill, resulting in contract assets. These contract assets are reported within receivables, net on our consolidated balance sheets and are invoiced in accordance with payment terms defined in each contract. Period end balances will vary from period to period due to agreed-upon contractual terms. Contract liabilities - Amounts are a result of billings in excess of costs incurred. Disaggregation of revenue from contracts with customers We disaggregate our revenue from contracts with customers by customer, contract type, as well as whether the Company acts as prime contractor or subcontractor. We believe these categories best depict how the nature, amount, timing and uncertainty of our revenue and cash flows are affected by economic factors.
Use of Estimates	Use of estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Significant estimates include valuation of goodwill and intangible assets, interest rate swaps, stock-based compensation, right of use assets and lease liabilities, valuation allowances established against accounts receivable and deferred tax assets, and measurement of loss development on workers’ compensation claims. We evaluate these estimates and judgments on an ongoing basis and base our estimates on historical experience, current and expected future outcomes, third-party evaluations and various other assumptions that we believe are reasonable under the circumstances. The results of these estimates form the basis for making judgments about the carrying values of assets and liabilities as well as identifying and assessing the accounting treatment with respect to commitments and contingencies. We revise material accounting estimates if changes occur, such as more experience is acquired, additional information is obtained, or there is new information on which an estimate was or can be based. Actual results could differ from those estimates. In particular, a material reduction in the fair value of goodwill could have a material adverse effect on the Company’s financial position and results of operations. We account for the effect of a change in accounting estimate during the period in which the change occurs.
Fair Value of Financial Instruments	Fair value of financial instruments The carrying amounts of the Company's cash and cash equivalents, accounts receivable, contract assets, accrued expenses, and accounts payable approximate fair value due to the short-term nature of these instruments. The fair values of the Company's debt instruments approximated fair value because the underlying interest rates approximate market rates that the Company could obtain for similar instruments at the balance sheet dates.
Goodwill and Other Intangible Assets	Goodwill and other intangible assets DLH continues to review its goodwill and other intangible assets for possible impairment or loss of value at least annually or more frequently upon the occurrence of an event or when circumstances indicate that a reporting unit’s carrying amount is greater than its fair value.
Long-lived Assets	Equipment and improvements Equipment and improvements are stated at cost. Depreciation and amortization are provided using the straight-line method over the estimated useful asset lives (3 to 7 years) and the shorter of the initial lease term or estimated useful life for leasehold improvements. Maintenance and repair costs are expensed as incurred.
Income Taxes	Income taxes DLH accounts for income taxes in accordance with the liability method, whereby deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities, using enacted tax rates in effect for the year in which the differences are expected to reverse. Deferred tax assets are reflected on the consolidated balance sheet when it is determined that it is more likely than not that the asset will be realized. This guidance also requires that deferred tax assets be reduced by a valuation allowance if it is more likely than not that some or all of the deferred tax asset will not be realized. We account for uncertain tax positions by recognizing the financial statement effects of a tax position only when, based upon the technical merits, it is "more-likely-than-not" that the position will be sustained upon examination. We had no uncertain tax positions at either December 31, 2019 or September 30, 2019. We report interest and penalties as a component of income tax expense. In the three months ended December 31, 2019 and December 31, 2018, we recognized no interest and no penalties related to income taxes.
Stock-based Equity Compensation	Stock-based equity compensation The Company uses the fair value-based method for stock-based equity compensation. Options issued are designated as either an incentive stock or a non-statutory stock option. No option may be granted with a term of more than 10 years from the date of grant. Option awards may depend on achievement of certain performance measures determined by the Compensation Committee of our Board. Shares issued upon option exercise are newly issued common shares. All awards to employees and non-employees are recorded at fair value on the date of the grant and expensed over the period of vesting. The Company uses a binomial simulation option pricing model to estimate the fair value of each stock option at the date of grant. Any consideration paid by the option holders to purchase shares is credited to capital stock.
Cash and Cash Equivalents	Cash and cash equivalents We consider all highly liquid investments with an original maturity of three months or less when purchased to be cash equivalents. We maintain cash balances at financial institutions that are insured by the Federal Deposit Insurance Corporation (“FDIC”) up to $250,000. Deposits held with financial institutions may exceed the $250,000 limit.
Earnings Per Share	Earnings per share Basic earnings per share is calculated by dividing income available to common shareholders by the weighted average number of common stock outstanding and restricted stock grants that vested or are likely to vest during the period. Diluted earnings per share is calculated by dividing income available to common shareholders by the weighted average number of basic common shares outstanding, adjusted to reflect potentially dilutive securities. Diluted earnings per share is calculated using the treasury stock method.
Treasury Stock	Treasury Stock The Company periodically purchases its own common stock that is traded on public markets as part of announced stock repurchase programs.
Interest Rate Swap	Interest Rate Swap The Company uses derivative financial instruments to manage interest rate risk associated with its variable rate debt. The Company's objective in using these interest rate derivatives is to manage its exposure to interest rate movements and reduce volatility of interest expense. The gains and losses due to changes in the fair value of the interest rate swap agreements completely offset changes in the fair value of the hedged portion of the underlying debt. Offsetting changes in fair value of both the interest rate swaps and the hedged portion of the underlying debt both are recognized in interest expense in the Consolidated Statements of Operations. The Company does not hold or issue any derivative instrument for trading or speculative purposes.