Benefit Plans - Schedule of Significant Actuarial Assumptions Used to Determine Net Periodic Pension Costs (Details) - Qualified Plan	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Weighted average assumed discount rate	4.43%	4.68%	4.27%
Weighted average expected long-term rate of return on plan assets	7.00%	7.00%	7.50%
Assumed long-term rate of annual compensation increases	4.50%	4.50%	4.50%