Retirement Benefit Plans (Summary of Net Periodic Benefit Costs) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 45	$ 45	$ 40
Interest cost on benefit obligations	8,441	8,008	8,068
Expected return on plan assets	(11,461)	(11,873)	(11,495)
Amortization of prior service cost	0	0	0
Recognized net loss	6,665	5,724	2,781
Net periodic benefit cost (benefit)	3,690	1,904	(606)
SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0
Interest cost on benefit obligations	389	345	364
Expected return on plan assets	0	0	0
Amortization of prior service cost	0	0	0
Recognized net loss	426	390	135
Net periodic benefit cost (benefit)	815	735	499
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0
Interest cost on benefit obligations	125	123	139
Expected return on plan assets	0	0	0
Amortization of prior service cost	14	73	73
Recognized net loss	35	47	5
Net periodic benefit cost (benefit)	$ 174	$ 243	$ 217