Long-Term Debt Amortization of Term Loans (Details) - 6 months ended Jun. 30, 2018 - Credit agreement [Member] $ in Thousands, £ in Millions	GBP (£)	USD ($)
United States Term Loan [Member]
Debt Instrument, Prepayment, Principal		$ 105,000
U.K. term loan [Member]
Debt Instrument, Prepayment, Principal	£ 15.0	19,800
December 31, 2019 | United States Term Loan [Member]
Debt Instrument, Periodic Payment, Principal		1,725
March 31, 2020 through March 31, 2023 | United States Term Loan [Member]
Debt Instrument, Periodic Payment, Principal		17,788
Maturity date - June 5, 2023 | United States Term Loan [Member]
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid		1,085,038
Maturity date - June 5, 2023 | U.K. term loan [Member]
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid		208,111
September 30, 2019 | U.K. term loan [Member]
Debt Instrument, Periodic Payment, Principal		2,058
December 31, 2019 through March 31, 2023 | U.K. term loan [Member]
Debt Instrument, Periodic Payment, Principal		$ 3,412