Retirement Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Weighted-average expected long-term rate of return			5.50%
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost on benefit obligations	$ 1,166	$ 1,675	$ 2,332	$ 3,350
Expected return on plan assets	(3,596)	(3,380)	(7,191)	(6,760)
Recognized net loss (gain)	1,020	993	2,039	1,985
Net periodic benefit (income) cost	(1,410)	(712)	(2,820)	(1,425)
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost on benefit obligations	6	12	13	23
Expected return on plan assets	0	0	0	0
Recognized net loss (gain)	9	6	17	12
Net periodic benefit (income) cost	15	18	30	35
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost on benefit obligations	4	12	8	25
Expected return on plan assets	0	0	0	0
Recognized net loss (gain)	(20)	(8)	(40)	(17)
Net periodic benefit (income) cost	$ (16)	$ 4	$ (32)	$ 8