Retirement Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Weighted-average expected long-term rate of return			5.75%
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost on benefit obligations	$ 1,531	$ 2,001	$ 4,881	$ 5,956
Expected return on plan assets	(3,380)	(2,815)	(10,140)	(8,445)
Recognized net loss	1,036	1,420	3,021	4,280
Net periodic benefit cost	(813)	606	(2,238)	1,791
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost on benefit obligations	12	16	35	48
Expected return on plan assets	0	0	0	0
Recognized net loss	5	4	17	11
Net periodic benefit cost	17	20	52	59
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost on benefit obligations	9	22	34	64
Expected return on plan assets	0	0	0	0
Recognized net loss	(38)	(2)	(55)	(10)
Net periodic benefit cost	$ (29)	$ 20	$ (21)	$ 54