Defined Benefit Plans - Defined Benefit Plans Narrative (Details) - Pension Plans, Defined Benefit [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment	$ 2,500	$ 0	$ 2,500	$ 0
Defined Benefit Plan, Plan Assets, Contributions by Employer	600		1,200
Defined Benefit Plan, Estimated Future Employer Contributions in Current Fiscal Year	$ 2,300		$ 2,300