Retirement Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 12	$ 11	$ 37	$ 34
Interest cost on benefit obligations	1,829	2,110	5,486	6,331
Expected return on plan assets	(3,074)	(3,067)	(9,222)	(8,596)
Amortization of prior service cost	0	0	0	0
Recognized net loss	1,466	1,666	4,398	4,998
Net periodic benefit cost	233	720	699	2,767
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost on benefit obligations	96	98	281	292
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	0	0	0	0
Recognized net loss	136	106	561	319
Net periodic benefit cost	232	204	842	611
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost on benefit obligations	19	32	69	94
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	0	4	0	11
Recognized net loss	(15)	8	0	26
Net periodic benefit cost	$ 4	$ 44	$ 69	$ 131