Long-Term Debt and Related Matters (Narrative - United Kingdom) (Details)	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2018 GBP (£)	Dec. 31, 2017 USD ($)
Line of Credit Facility
Line of credit facility, amount outstanding	$ 74,008,000		$ 128,470,000
Foreign Line of Credit | Natwest Bank
Line of Credit Facility
Line of credit facility, maximum borrowing capacity	1,924,000	£ 1,500,000
Line of credit facility, amount outstanding	0
Line of credit facility, current borrowing capacity	$ 1,606,000		$ 1,494,000
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	$ 318,000