Long-term Debt Amortization of Term Loans (Details) - 12 months ended Dec. 31, 2017 - Credit Agreement [Member] £ in Thousands, $ in Millions	GBP (£)	USD ($)	USD ($)
United States Term Loan [Member]
Debt Instrument, Periodic Payment, Principal | $		$ 5.2
Debt Instrument, Prepayment, Principal | $		209.8
British pound term loan [Member]
Debt Instrument, Periodic Payment, Principal	£ 5,100	$ 6.7
March 31, 2018 through June 30, 2018 [Member] | British pound term loan [Member]
Debt Instrument, Periodic Payment, Principal | £	1,271
September 30, 2018 through December 31, 2019 [Member] | British pound term loan [Member]
Debt Instrument, Periodic Payment, Principal | £	2,542
Maturity date - March 31, 2020 [Member] | United States Term Loan [Member]
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid | $			$ 1,200.0
Maturity date - March 31, 2020 [Member] | British pound term loan [Member]
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid | £	£ 75,532