Retirement Benefit Plans (Changes in Other Comprehensive Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net (gain) loss	$ 368	$ 8,719	$ 33,567
Amounts reclassified from AOCL	(7,126)	(6,161)	(2,921)
Total (gain) loss recognized in OCI	(6,772)	2,485	30,573
Pension Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net (gain) loss	(715)	8,525	31,951
Amounts reclassified from AOCL	(6,665)	(5,724)	(2,781)
Amortization of prior service cost	0	0	0
Total (gain) loss recognized in OCI	(7,380)	2,801	29,170
SERP [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net (gain) loss	1,023	372	1,145
Amounts reclassified from AOCL	(426)	(390)	(134)
Amortization of prior service cost	0	0	0
Total (gain) loss recognized in OCI	597	(18)	1,011
Other Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net (gain) loss	60	(178)	470
Amounts reclassified from AOCL	(35)	(47)	(5)
Amortization of prior service cost	(14)	(73)	(73)
Total (gain) loss recognized in OCI	$ 11	$ (298)	$ 392