Retirement Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost on benefit obligations	$ 1,675	$ 1,978
Expected return on plan assets	(3,380)	(2,815)
Recognized net loss	992	1,430
Net periodic benefit (benefit) cost	(713)	593
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost on benefit obligations	11	16
Expected return on plan assets	0	0
Recognized net loss	6	4
Net periodic benefit (benefit) cost	17	20
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost on benefit obligations	13	21
Expected return on plan assets	0	0
Recognized net loss	(9)	(4)
Net periodic benefit (benefit) cost	$ 4	$ 17