Summary of Significant Accounting Policies - Concentration (Details) - contract	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Maximum
Risk Associated with Certain Concentrations
Term for release of funds to the seller	30 days
Revenue | Contract with commercial client
Risk Associated with Certain Concentrations
Concentration Risk, Percentage	9.70%
U.S. Department of Defense
Risk Associated with Certain Concentrations
Number of Contracts	2
U.S. Department of Defense | Revenue | Surplus Contract
Risk Associated with Certain Concentrations
Concentration Risk, Percentage	31.00%	24.70%	26.80%
U.S. Department of Defense | Revenue | Scrap Contract
Risk Associated with Certain Concentrations
Concentration Risk, Percentage	10.20%	15.30%	14.40%