Retirement Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost on benefit obligations	$ 1,977	$ 1,935	$ 3,955	$ 3,720
Expected return on plan assets	(2,815)	(3,180)	(5,630)	(6,360)
Recognized net loss	1,430	1,160	2,860	2,320
Net periodic benefit cost	592	(85)	1,185	(320)
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost on benefit obligations	16	(21)	32	166
Expected return on plan assets	0	0	0	0
Recognized net loss	3	333	7	458
Net periodic benefit cost	19	312	39	624
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost on benefit obligations	21	19	42	39
Expected return on plan assets	0	0	0	0
Recognized net loss	(4)	0	(8)	0
Net periodic benefit cost	$ 17	$ 19	$ 34	$ 39