U.K. Pension Plan Assumptions (Details) - Pension Plan [Member] - Foreign Plan [Member] - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.80%	2.40%	2.70%
Price inflation (RPI measure)	3.10%	3.30%	3.30%
Pension increases (CPI measure)	2.00%	2.20%	2.20%
Salary increases	3.70%	3.30%	3.30%
Discount rate	3.20%	2.70%	3.80%
Price inflation (RPI measure)	3.00%	3.30%	3.10%
Pension increases (CPI measure)	1.70%	2.20%	2.00%
Salary increases	3.40%	3.30%	3.70%
Expected return on plan assets	6.10%	6.00%	6.10%
Discount Rate 1% per annum		$ (76,022)
Discount Rate -1% per annum		100,641
RPI inflation 1% per annum		99,559
RPI inflation -1% per annum		$ (76,833)