Defined Benefit Post-Retirement Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Defined Benefit Post-Retirement Plans [Abstract]
Employer contributions	$ 0	$ 0	$ 0	$ 0
Pension Benefits [Member]
Components of net periodic cost (benefit) [Abstract]
Service cost	435	420	870	840
Interest cost	981	920	1,962	1,840
Expected return on plan assets	(1,873)	(2,123)	(3,746)	(4,246)
Net amortization	639	251	1,278	502
Total net periodic cost (benefit)	182	(532)	364	(1,064)
Other Benefits [Member]
Components of net periodic cost (benefit) [Abstract]
Service cost	2	3	4	6
Interest cost	81	82	162	164
Expected return on plan assets	0	0	0	0
Net amortization	18	44	35	88
Total net periodic cost (benefit)	$ 101	$ 129	$ 201	$ 258