Long-Term Debt and Related Matters (Narrative - United Kingdom) (Details)	6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2017 GBP (£)	Dec. 31, 2016 USD ($)
Line of Credit Facility [Line Items]
Line of credit facility, amount outstanding	$ 120,617,000		$ 127,073,000
NatWest Bank [Member] | Foreign Line of Credit
Line of Credit Facility [Line Items]
Line of credit Facility, maximum borrowing capacity	1,954,000	£ 1,500,000
Line of credit facility, amount outstanding	0
Line of credit facility, current borrowing capacity	$ 1,553,000
NatWest Bank [Member] | Foreign Line of Credit | Base Rate
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate	2.50%
Natwest Bank Outstanding Guarantees | Foreign Line of Credit
Line of Credit Facility [Line Items]
Line of credit facility, amount outstanding	$ 401,000