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Retirement Benefits (Schedule of Costs of Retirement Plans) (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Mar. 31, 2018
Mar. 31, 2017
Retirement Benefits [Abstract]        
Company Costs - Defined Contribution $ 8,716 $ 8,502 $ 16,595 $ 15,751
Company Contributions - Multiemployer plan $ 87 $ 79 $ 167 $ 147