Long-term Debt Outstanding Revolving Loans (Details) - Revolving credit facility [Member] € in Thousands, £ in Thousands, CAD in Thousands, $ in Thousands	Dec. 31, 2017 GBP (£)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 EUR (€)	Dec. 31, 2017 CAD
British pound [Member]
Line of Credit Facility [Line Items]
Long-term Debt, Gross	£ 144,000	$ 194,789
Debt Instrument, Interest Rate, Stated Percentage	1.99%	1.99%	1.99%	1.99%
Canadian dollar [Member]
Line of Credit Facility [Line Items]
Long-term Debt, Gross		$ 3,195		CAD 4,000
Debt Instrument, Interest Rate, Stated Percentage	2.91%	2.91%	2.91%	2.91%
Euro [Member]
Line of Credit Facility [Line Items]
Long-term Debt, Gross		$ 30,656	€ 25,500
Debt Instrument, Interest Rate, Stated Percentage	1.50%	1.50%	1.50%	1.50%