Retirement Benefits (Schedule of estimated remaining cash contributions) (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Other Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated future employer contributions in the currect fiscal year	$ 3,645
UNITED STATES | Defined Benefit Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated future employer contributions in the currect fiscal year	0
UNITED KINGDOM | Defined Benefit Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated future employer contributions in the currect fiscal year	297
JAPAN | Defined Benefit Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated future employer contributions in the currect fiscal year	$ 0