Employee Benefit Plans - Other Postretirement Benefits (Narrative) (Details) - Other postretirement benefits - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Discount rate used to measure net periodic benefit cost	4.39%	4.01%	4.73%
Discount rate used to measure accumulated postretirement benefit obligation	4.15%	4.39%
Estimated future benefit payments 2017	$ 0.4
Estimated future benefit payments 2018	0.4
Estimated future benefit payments 2019	0.4
Estimated future benefit payments 2020	0.4
Estimated future benefit payments 2021	0.4
Estimated future benefit payments, five years thereafter	$ 2.2