Contingencies - Litigation and Other Matters (Details) - USD ($)	Dec. 31, 2017	Sep. 30, 2017
Loss Contingencies [Line Items]
Estimated litigation liability	$ 0
Legal Reserve
Loss Contingencies [Line Items]
Accrued amounts for litigation and other contingent liabilities	4,000,000	$ 3,900,000
Performance Bonds
Loss Contingencies [Line Items]
Letters of credit secured using cash collateral	44,900,000
Outstanding performance bonds	$ 229,300,000