Employee Benefit Plans - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) pension_plan	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Number of qualified defined benefit plans | pension_plan	1
Pension contribution requirements in next fiscal year | $	$ 2.9
Pension
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.48%	4.01%	4.20%
Expected long-term return on plan assets, percent	7.17%	7.70%	7.70%