Long-term Debt Outstanding Revolving Loans (Details) - Revolving credit facility [Member] £ in Thousands, $ in Thousands	Dec. 31, 2018 GBP (£)	Dec. 31, 2018 USD ($)
United States Revolving Loan [Member]
Line of Credit Facility [Line Items]
Long-term Debt, Gross		$ 135,000
Debt Instrument, Interest Rate, Stated Percentage	4.02%	4.02%
United States Swingline Loan [Member]
Line of Credit Facility [Line Items]
Long-term Debt, Gross		$ 10,000
Debt Instrument, Interest Rate, Stated Percentage	6.00%	6.00%
British Pound Swingline Loan [Member]
Line of Credit Facility [Line Items]
Long-term Debt, Gross	£ 15,000	$ 19,136
Debt Instrument, Interest Rate, Stated Percentage	2.23%	2.23%