Long-Term Debt Amortization of Term Loans (Details) - 9 months ended Sep. 30, 2018 - Credit agreement [Member] $ in Thousands, £ in Millions	GBP (£)	USD ($)
United States Term Loan [Member]
Debt Instrument, Prepayment, Principal		$ 120,000
U.K. term loan [Member]
Debt Instrument, Prepayment, Principal	£ 25.0	32,800
March 31, 2020 | United States Term Loan [Member]
Debt Instrument, Periodic Payment, Principal		4,513
June 30, 2020 through March 31, 2023 | United States Term Loan [Member]
Debt Instrument, Periodic Payment, Principal		17,788
June 30, 2020 | U.K. term loan [Member]
Debt Instrument, Periodic Payment, Principal		2,293
September 30, 2020 through March 31, 2023 | U.K. term loan [Member]
Debt Instrument, Periodic Payment, Principal		3,412
Maturity date - June 5, 2023 | United States Term Loan [Member]
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid		1,085,031
Maturity date - June 5, 2023 | U.K. term loan [Member]
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid		$ 208,111