Employee Benefit Plans Summary of Pension Plan and Postretirement Plan Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 763	$ 830	$ 2,290	$ 2,490
Expected return on plan assets	(512)	(451)	(1,536)	(1,353)
Net amortization and deferral	607	663	1,822	1,989
Net periodic benefit	858	1,042	2,576	3,126
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	13	17	42	51
Net accretion and deferral	(139)	(141)	(419)	(423)
Net periodic benefit	$ (126)	$ (124)	$ (377)	$ (372)