Long-Term Debt and Related Matters (Narrative - United States) (Details)			3 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
	Nov. 07, 2016 USD ($)	Jun. 29, 2016 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2017	Dec. 31, 2016 USD ($)
Line of Credit Facility [Line Items]
Term loan					$ 13,131,000		$ 30,000,000
Line of credit facility, amount outstanding					123,494,000		$ 127,073,000
PNC Bank, N.A., Bank of America, N.A., Wells Fargo Bank, N.A., Citizens Bank of Pennsylvania, and Branch Banking and Trust Company
Line of Credit Facility [Line Items]
Line of credit Facility, maximum borrowing capacity	$ 195,000,000	$ 275,000,000
Term loan	$ 30,000,000
Leverage ratio in effect for the seventh quarter of a credit agreement	4.25
Leverage ratio in effect for the eighth quarter and remainder of a credit agreement	3.75
EBITDA required			$ 18,500,000		23,000,000
EBITDA required for seventh quarter					31,000,000
Maximum dividends, distributions, or redemptions allowed	$ 1,700,000	4,000,000
Loans and advances limit	5,000,000	10,000,000
Maximum asset sales allowed	25,000,000	25,000,000
Carryover of asset sales allowed	$ 15,000,000	$ 15,000,000
PNC Bank, N.A., Bank of America, N.A., Wells Fargo Bank, N.A., Citizens Bank of Pennsylvania, and Branch Banking and Trust Company | Euro-rate
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate	3.25%
PNC Bank, N.A., Bank of America, N.A., Wells Fargo Bank, N.A., Citizens Bank of Pennsylvania, and Branch Banking and Trust Company | Euro-rate | Lowest Tier
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate	2.50%
PNC Bank, N.A., Bank of America, N.A., Wells Fargo Bank, N.A., Citizens Bank of Pennsylvania, and Branch Banking and Trust Company | Base Rate
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate	2.25%
PNC Bank, N.A., Bank of America, N.A., Wells Fargo Bank, N.A., Citizens Bank of Pennsylvania, and Branch Banking and Trust Company | Base Rate | Lowest Tier
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate	1.50%
PNC Bank, N.A., Bank of America, N.A., Wells Fargo Bank, N.A., Citizens Bank of Pennsylvania, and Branch Banking and Trust Company | Forecasted
Line of Credit Facility [Line Items]
Fixed charge coverage ratio						1.00
Fixed charge coverage ratio after fifth quarter				1.25
Liquidity covenant				$ 25,000,000
PNC Bank, N.A., Bank of America, N.A., Wells Fargo Bank, N.A., Citizens Bank of Pennsylvania, and Branch Banking and Trust Company | Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility, amount outstanding					425,000
Line of credit facility, current borrowing capacity					$ 46,081,000