Employee Benefit Plans - Supplemental Non-qualified Unfunded Plans (Narrative) (Details) - Other postretirement benefits - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Net periodic pension cost, Discount rate (as a percent)	3.65%	4.16%	4.39%
Officers and Key Employees
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Net periodic pension cost, Discount rate (as a percent)	2.16%	1.91%	4.14%
Amount accrued	$ 2.3	$ 2.1