Retirement Plans (Strategic Allocation of Plan Assets) (Details)	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Strategic asset allocation
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	100.00%
Actual asset allocations
Actual plan asset allocations	100.00%	100.00%	100.00%
Equity Securities [Member]
Strategic asset allocation
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	20.00%	30.00%	40.00%
Actual asset allocations
Actual plan asset allocations	21.00%	29.00%	39.00%
Large Capitalization Stocks [Member]
Strategic asset allocation
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	12.00%
Small Capitalization Stocks [Member]
Strategic asset allocation
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	3.00%
International Stocks [Member]
Strategic asset allocation
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	5.00%
Fixed Income Securities [Member]
Strategic asset allocation
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	80.00%
Fixed Income Funds [Member]
Actual asset allocations
Actual plan asset allocations	78.00%	69.00%	60.00%
Cash and Cash Equivalents [Member]
Strategic asset allocation
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	0.00%
Actual asset allocations
Actual plan asset allocations	1.00%	2.00%	1.00%
Minimum [Member] | Equity Securities [Member]
Strategic asset allocation
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	15.00%
Minimum [Member] | Fixed Income Funds [Member]
Strategic asset allocation
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage
Minimum [Member] | Cash and Cash Equivalents [Member]
Strategic asset allocation
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	0.00%
Maximum [Member] | Fixed Income Funds [Member]
Strategic asset allocation
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	80.00%
Maximum [Member] | Cash and Cash Equivalents [Member]
Strategic asset allocation
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	5.00%