Retirement Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 13	$ 11	$ 25	$ 23
Interest cost on benefit obligations	1,844	2,123	3,657	4,221
Expected return on plan assets	(3,075)	(2,964)	(6,148)	(5,529)
Amortization of prior service cost	0	0	0	0
Recognized net loss	1,515	1,642	2,932	3,332
Net periodic benefit cost	297	812	466	2,047
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost on benefit obligations	93	97	185	194
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	0	0	0	0
Recognized net loss	212	83	425	213
Net periodic benefit cost	305	180	610	407
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost on benefit obligations	25	31	50	62
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	0	3	0	7
Recognized net loss	7	9	15	18
Net periodic benefit cost	$ 32	$ 43	$ 65	$ 87