Retirement Plans - Weighted Average Asset Allocations (Details) - Pension Plans, Defined Benefit [Member]	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted average asset allocations	100.00%	100.00%
U.S. Equities securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted average asset allocations	50.00%	72.00%
U.S. Debt securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted average asset allocations	50.00%	24.00%
Cash [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted average asset allocations		4.00%