Employee Benefits - Components of Net Periodic Pension Cost and Other Changes in Plan Assets and Benefit (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Components of Net Periodic Pension Cost
Interest cost on projected benefit obligation	$ 978	$ 1,025	$ 2,912	$ 3,075
Expected return on plan assets	(1,566)	(1,582)	(4,700)	(4,746)
Net amortization	512	475	1,601	1,424
Net Periodic Pension Expense	$ (76)	$ (82)	$ (187)	$ (247)