Financing Arrangements (Narrative) (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) credit_line	May 31, 2023 USD ($)	Jul. 31, 2022 USD ($)	Dec. 31, 2017 EUR (€) credit_line	Dec. 31, 2016 USD ($)
Line of Credit Facility [Line Items]
Long-term notes, current portion	$ 3,604,000				$ 3,188,000
Long-term notes
Line of Credit Facility [Line Items]
Long-term debt	48,982,000				40,823,000
Long-term notes, current portion	3,604,000				$ 3,188,000
Unsecured Debt
Line of Credit Facility [Line Items]
Notes payable	21,969,000
Notes payable, current	$ 1,188,000
Unsecured Debt | Scenario, Forecast
Line of Credit Facility [Line Items]
Notes payable		$ 15,438,000
Unsecured Debt | Interest rate swap
Line of Credit Facility [Line Items]
Fixed interest rate swap percentage	2.85%			2.85%
Secured Debt
Line of Credit Facility [Line Items]
Notes payable	$ 27,013,000
Notes payable, current	$ 2,416,000
Interest rate percentage	2.74%			2.74%
Secured Debt | Scenario, Forecast
Line of Credit Facility [Line Items]
Notes payable			$ 15,375,000
London Interbank Offered Rate (LIBOR) | Unsecured Debt
Line of Credit Facility [Line Items]
Percentage over LIBOR	1.20%
U.S. Line Of Credit
Line of Credit Facility [Line Items]
Aggregate available principal under credit facility	$ 50,000,000
Total drawings under credit facility	0
Guarantor obligations, maximum exposure, undiscounted	520,000
Aggregate remaining availability	$ 49,480,000
U.S. Line Of Credit | Minimum | London Interbank Offered Rate (LIBOR)
Line of Credit Facility [Line Items]
Percentage over LIBOR	0.80%
U.S. Line Of Credit | Maximum | London Interbank Offered Rate (LIBOR)
Line of Credit Facility [Line Items]
Percentage over LIBOR	1.20%
U.S. Long-Term note
Line of Credit Facility [Line Items]
Debt service coverage ratio (greater than)	1.5
Maximum indebtedness multiplier against EBITDA covenant	3
U.S. Long-Term note | Minimum
Line of Credit Facility [Line Items]
Covenant compliance	$ 50,000
U.S. Long-Term note | Maximum
Line of Credit Facility [Line Items]
Covenant compliance	250,000
Euro Line Of Credit
Line of Credit Facility [Line Items]
Aggregate available principal under credit facility	59,893,000			€ 50,000,000
Total drawings under credit facility	0
Guarantor obligations, maximum exposure, undiscounted	798,000
Aggregate remaining availability	59,095,000
Euro Overdraft Facilities
Line of Credit Facility [Line Items]
Aggregate available principal under credit facility	599,000			500,000
Total drawings under credit facility	0
Aggregate remaining availability	599,000
Other European Facilities
Line of Credit Facility [Line Items]
Aggregate available principal under credit facility	1,797,000			€ 1,500,000
Total drawings under credit facility	0
Aggregate remaining availability	$ 1,797,000
Number of credit lines | credit_line	2			2