Retirement Plans - Information about Plan Assets (Details)	Dec. 31, 2017	Dec. 31, 2016
United States
Defined Benefit Plan, Information about Plan Assets [Abstract]
Actual plan asset allocations	100.00%	100.00%
United States | Short-term investments
Defined Benefit Plan, Information about Plan Assets [Abstract]
Actual plan asset allocations	1.00%	1.00%
United States | Fixed income securities
Defined Benefit Plan, Information about Plan Assets [Abstract]
Actual plan asset allocations	27.00%	60.00%
United States | Equity securities
Defined Benefit Plan, Information about Plan Assets [Abstract]
Actual plan asset allocations	72.00%	39.00%
United States | Other investments | Insurance contracts
Defined Benefit Plan, Information about Plan Assets [Abstract]
Actual plan asset allocations	0.00%	0.00%
International
Defined Benefit Plan, Information about Plan Assets [Abstract]
Actual plan asset allocations	100.00%	100.00%
International | Short-term investments
Defined Benefit Plan, Information about Plan Assets [Abstract]
Actual plan asset allocations	0.00%	0.00%
International | Fixed income securities
Defined Benefit Plan, Information about Plan Assets [Abstract]
Actual plan asset allocations	0.00%	0.00%
International | Equity securities
Defined Benefit Plan, Information about Plan Assets [Abstract]
Actual plan asset allocations	0.00%	0.00%
International | Other investments | Insurance contracts
Defined Benefit Plan, Information about Plan Assets [Abstract]
Actual plan asset allocations	100.00%	100.00%