Employee Benefit Plans - Assumptions Used in Calculations (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate, percent	3.48%	4.01%	4.20%
Rate of compensation, percent	0.00%	4.16%	4.50%
Assumptions used to determine net periodic benefit cost for years ended December 31:
Discount rate (post-spin off), percent	4.01%	4.20%	3.80%
Expected long-term return on plan assets, percent	7.17%	7.70%	7.70%
Rate of compensation increase, percent	0.00%	4.16%	4.50%
Postretirement
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate, percent	3.56%	4.12%	4.34%
Rate of compensation, percent	4.50%	4.50%	4.50%
Assumptions used to determine net periodic benefit cost for years ended December 31:
Discount rate (post-spin off), percent	4.12%	4.34%	3.96%
Expected long-term return on plan assets, percent	0.00%	0.00%	0.00%
Rate of compensation increase, percent	4.50%	4.50%	4.50%