Retirement Benefit Plans (Summary of Components of Accumulated Other Comprehensive Loss Related to Pensions and Postretirement Benefits) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Deferred tax benefit		$ (2,502)	$ 918	$ 11,147
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ 73,238	65,857	73,238
Prior service cost	0	0	0
Total pre-tax amounts included in AOCL	73,238	65,857	73,238
Deferred tax benefit	26,447	23,727
Amounts included in accumulated AOCL, net of tax	46,791	42,130	46,791
SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	2,412	3,009	2,412
Prior service cost	0	0	0
Total pre-tax amounts included in AOCL	2,412	3,009	2,412
Deferred tax benefit	871	1,084
Amounts included in accumulated AOCL, net of tax	1,541	1,925	1,541
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	591	616	591
Prior service cost	14	0	14
Total pre-tax amounts included in AOCL	605	616	605
Deferred tax benefit	218	222
Amounts included in accumulated AOCL, net of tax	$ 387	$ 394	$ 387