Employee Benefit Plans - Summary of Assumptions Used to Determine Benefit Obligations For Defined Benefit Plans (Details)	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans [Member]
Assumptions used to determine defined benefit plan obligations [Abstract]
Discount rate	3.23%	3.60%
Rate of compensation increases	3.61%	4.20%
SERP [Member]
Assumptions used to determine defined benefit plan obligations [Abstract]
Discount rate	2.92%	3.13%
Rate of compensation increases	3.13%	3.37%