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Summary of Significant Accounting Polices - EPS (Details)
shares in Thousands, $ in Millions
12 Months Ended
Sep. 30, 2017
USD ($)
item
shares
Sep. 30, 2016
shares
Sep. 30, 2015
contract
shares
Revenue Recognition      
Number of estimates, a change in which could have material effect on financial position or results of operations | item 1    
Allocation of arrangement consideration to the up-front deliverables | $ $ 0.0    
Revenue for the delivery of up-front units of accounting | $ $ 0.0    
Number of transportation systems service contracts, which contain annual system usage incentives | contract     1
Stock-Based Compensation      
Vesting period of performance-based RSUs 3 years    
Net Income Per Share      
Anti-dilutive employee share-based awards 0 0 0
Weighted average shares - basic 27,106 26,976 26,872
Effect of dilutive securities     66
Weighted average shares - diluted 27,106 26,976 26,938
Number of anti-dilutive securities 967 825