Employee Benefit Plans (Narrative) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Decrease in defined benefit plan obligation	$ 105,400	$ 102,369
Defined benefit pension plan
Defined Benefit Plan Disclosure [Line Items]
Cash balance revaluation discount rate	4.17%
Change in assumptions for defined benefit plans | Defined benefit pension plan
Defined Benefit Plan Disclosure [Line Items]
Decrease in defined benefit plan obligation	$ 3,300