Employee Benefit Plans Narrative (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Decrease in defined benefit plan obligation	$ 106,934	$ 102,369
Defined benefit pension plan
Defined Benefit Plan Disclosure [Line Items]
Cash balance revaluation discount rate	4.11%
Change in assumptions for defined benefit plans | Defined benefit pension plan
Defined Benefit Plan Disclosure [Line Items]
Decrease in defined benefit plan obligation	$ 5,000