Long-Term Debt (Narrative - United Kingdom) (Details)	3 Months Ended
	Mar. 31, 2019 GBP (£)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Line of Credit Facility
Line of credit facility, amount outstanding		$ 89,389,000	$ 74,008,000
Foreign Line of Credit | Natwest Bank
Line of Credit Facility
Line of credit facility, maximum borrowing capacity	£ 1,500,000	1,955,000
Line of credit facility, amount outstanding		0
Line of credit facility, current borrowing capacity		1,355,000
Foreign Line of Credit | Natwest Bank | Base Rate
Line of Credit Facility
Debt instrument, basis spread on variable rate	2.50%
Foreign Line of Credit | Natwest Bank Outstanding Guarantees
Line of Credit Facility
Line of credit facility, amount outstanding		$ 600,000