Retirement Benefit Plans (Components of Net Periodic Benefits Cost) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Total recognized in other comprehensive income	$ (2,398)		$ 45,198		$ 10,929
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	10,981		12,414		15,381
Interest cost	18,843		16,762		16,514
Expected return on plan assets	(45,199)		(41,033)		(37,632)
Amortization of net loss/ prior service cost	10,087		5,423		5,554
Net periodic benefit cost	(5,288)		(6,434)		(183)
Net (loss) gain recognized during the year	(10,087)		(5,423)		(5,554)
Net actuarial loss (gain)	(3,131)		51,915		(7,378)
Total recognized in other comprehensive income	(13,218)		46,492		(12,932)
Total recognized in net periodic benefit cost and other comprehensive income	$ (18,506)		$ 40,058		$ (13,115)
Discount rate for benefit obligations	3.14%		4.14%		3.57%
Discount rate for net periodic benefit cost	4.14%		3.57%		4.10%
Expected long-term return on plan assets	7.25%		7.25%		7.25%
Rate of compensation increase		[1]		[2]		[2]
Pension Benefits [Member] | Graded Scale, At Age 20 [Member]
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase	7.25%		7.25%		7.25%
Pension Benefits [Member] | Graded Scale, At Age 60 [Member]
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase	2.25%		2.25%		2.25%
Pension Benefits [Member] | Graded Scale, 7.00% At Age 20 [Member]
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase	7.00%		7.00%		7.00%
Pension Benefits [Member] | Graded Scale, 2.00% At Age 60 [Member]
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase	2.00%		2.00%		2.00%
Other Post-Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 95		$ 120		$ 129
Interest cost	621		621		668
Amortization of net loss/ prior service cost	(913)		(434)		(353)
Net periodic benefit cost	(197)		307		444
Net (loss) gain recognized during the year	913		434		353
Net actuarial loss (gain)	733		(6,717)		993
Total recognized in other comprehensive income	1,646		(6,283)		1,346
Total recognized in net periodic benefit cost and other comprehensive income	$ 1,449		$ (5,976)		$ 1,790
Discount rate for benefit obligations	3.11%		4.10%		3.52%
Discount rate for net periodic benefit cost	4.10%		3.52%		3.95%

[1] Graded scale, declining from 7.25% at age 20 to 2.25% at age 60

[2] Graded scale, declining from 7.00% at age 20 to 2.00% at age 60