Long-Term Debt and Related Matters (Narrative - United Kingdom) (Details)	9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2017 GBP (£)	Dec. 31, 2016 USD ($)
Line of Credit Facility [Line Items]
Line of credit facility, amount outstanding	$ 123,494,000		$ 127,073,000
Foreign Line of Credit | NatWest Bank [Member]
Line of Credit Facility [Line Items]
Line of credit Facility, maximum borrowing capacity	2,010,000	£ 1,500,000
Line of credit facility, amount outstanding	0
Line of credit facility, current borrowing capacity	1,011,000
Foreign Line of Credit | Natwest Bank Outstanding Guarantees
Line of Credit Facility [Line Items]
Line of credit facility, amount outstanding	$ 999,000
Foreign Line of Credit | Base Rate | NatWest Bank [Member]
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate	2.50%