Retirement Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 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	$ 1,675	$ 1,977	$ 3,350	$ 3,955
Expected return on plan assets	(3,380)	(2,815)	(6,760)	(5,630)
Recognized net loss	993	1,430	1,985	2,860
Net periodic benefit cost	(712)	592	(1,425)	1,185
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost on benefit obligations	12	16	23	32
Expected return on plan assets	0	0	0	0
Recognized net loss	6	3	12	7
Net periodic benefit cost	18	19	35	39
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost on benefit obligations	12	21	25	42
Expected return on plan assets	0	0	0	0
Recognized net loss	(8)	(4)	(17)	(8)
Net periodic benefit cost	$ 4	$ 17	$ 8	$ 34