Retirement Plans - Pension Plan Asset Allocation (Details 7)	Dec. 31, 2018	Dec. 31, 2017
Retirement Plans
Target allocations	100.00%
Percentage of plan assets	100.00%	100.00%
Equity Securities
Retirement Plans
Target allocations	13.00%
Percentage of plan assets	12.00%	11.00%
Debt securities
Retirement Plans
Target allocations	83.00%
Percentage of plan assets	84.00%	82.00%
Other
Retirement Plans
Target allocations	4.00%
Percentage of plan assets	4.00%	7.00%