Retirement Benefit Plans (Components of Net Periodic Benefits Cost) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 14,098	$ 13,511	$ 12,920
Interest cost	16,907	18,635	19,251
Expected return on plan assets	(34,554)	(32,833)	(32,222)
Amortization of net loss/ prior service cost	5,783	3,169	26
Net periodic benefit cost	2,234	2,482	(25)
Net (loss) gain recognized during the year	(5,783)	(3,169)	(26)
Net actuarial loss (gain)	12,128	39,876	44,599
Total recognized in other comprehensive income	6,345	36,707	44,573
Total recognized in net periodic benefit cost and other comprehensive income	$ 8,579	$ 39,189	$ 44,548
Discount rate for benefit obligations	4.10%	4.40%	4.11%
Discount rate for net periodic benefit cost	4.40%	4.11%	4.73%
Expected long-term return on plan assets	7.25%	7.50%	7.50%
Pension Benefits [Member] | Graded Scale, At Age 20 [Member]
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase	7.00%	7.00%
Pension Benefits [Member] | Graded Scale, At Age 60 [Member]
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase	2.00%	2.00%
Other Post-Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 170	$ 117	$ 126
Interest cost	773	891	1,140
Amortization of net loss/ prior service cost	145	6	364
Net periodic benefit cost	1,088	1,014	1,630
Net (loss) gain recognized during the year	(145)	(6)	(364)
Net actuarial loss (gain)	620	(5,905)	(3,467)
Total recognized in other comprehensive income	475	(5,911)	(3,831)
Total recognized in net periodic benefit cost and other comprehensive income	$ 1,563	$ (4,897)	$ (2,201)
Discount rate for benefit obligations	3.95%	4.32%	4.02%
Discount rate for net periodic benefit cost	4.32%	4.02%	4.58%