Significant Accounting Policies - Revenue by Major Customers (Details) - Revenues - Customer Concentration Risk |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Mar. 31, 2021 |
Mar. 31, 2020 |
Mar. 31, 2021 |
Mar. 31, 2020 |
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| Department of Transportation | ||||
| Concentration Risk [Line Items] | ||||
| Concentration risk percentage | 26.10% | 27.80% | 27.00% | 29.40% |
| Private | ||||
| Concentration Risk [Line Items] | ||||
| Concentration risk percentage | 41.80% | 39.40% | 41.20% | 39.40% |
| Public | ||||
| Concentration Risk [Line Items] | ||||
| Concentration risk percentage | 58.20% | 60.60% | 58.80% | 60.60% |
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- 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. No definition available.
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- 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. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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