Annual report pursuant to Section 13 and 15(d)

Short-Term Borrowings and Credit Lines (Narrative) (Details)

v3.8.0.1
Short-Term Borrowings and Credit Lines (Narrative) (Details)
 12 Months Ended
Dec. 31, 2017
USD ($)
Dec. 31, 2017
EUR (€)
Dec. 31, 2017
JPY (¥)
Dec. 31, 2017
CAD
Dec. 31, 2016
USD ($)
Line of Credit Facility [Line Items]          
Available credit amount $ 100,000,000        
Domestic [Member] | Unsecured And Uncommitted Line Of Credit [Member]          
Line of Credit Facility [Line Items]          
Long-term Line of Credit $ 0       $ 0
Canadian Subsidiary [Member] | Unsecured And Uncommitted Line Of Credit [Member]          
Line of Credit Facility [Line Items]          
Interest rate description Canadian prime rate        
Proceeds from Lines of Credit         0
Maximum borrowing capacity $ 23,866,000     CAD 30,000,000  
Long-term Line of Credit 0        
European Subsidiary [Member]          
Line of Credit Facility [Line Items]          
Long-term Line of Credit 0       0
European Subsidiary [Member] | Unsecured And Uncommitted Line Of Credit [Member]          
Line of Credit Facility [Line Items]          
Maximum borrowing capacity $ 36,784,000        
European Subsidiary [Member] | Unsecured And Uncommitted Credit Line1 [Member]          
Line of Credit Facility [Line Items]          
Interest rate description European Central Bank ("ECB") refinancing rate plus 100 basis points        
Maximum borrowing capacity | €   € 25,800,000      
European Subsidiary [Member] | Unsecured And Uncommitted Credit Line2 [Member]          
Line of Credit Facility [Line Items]          
Interest rate description Euro Overnight Index Average ("EONIA") plus 75 basis points        
Maximum borrowing capacity | €   € 5,000,000      
Japanese Subsidiary [Member] | Unsecured And Uncommitted Line Of Credit [Member]          
Line of Credit Facility [Line Items]          
Maximum borrowing capacity $ 9,658,000        
Japanese Subsidiary [Member] | Unsecured And Uncommitted Credit Line1 [Member]          
Line of Credit Facility [Line Items]          
Interest rate description JPY LIBOR plus 100 basis points        
Maximum borrowing capacity $ 7,000,000        
Japanese Subsidiary [Member] | Unsecured And Uncommitted Credit Line2 [Member]          
Line of Credit Facility [Line Items]          
Interest rate description Bank of Tokyo Prime Rate        
Maximum borrowing capacity | ¥     ¥ 300,000,000    
Japanese Subsidiary [Member] | Revolving Line Of Credit [Member]          
Line of Credit Facility [Line Items]          
Long-term Line of Credit $ 0       0
Korean Subsidiary [Member]          
Line of Credit Facility [Line Items]          
Long-term Line of Credit $ 0       $ 0
Korean Subsidiary [Member] | Unsecured And Uncommitted Line Of Credit [Member]          
Line of Credit Facility [Line Items]          
Interest rate description CD rate plus 220 basis points        
Maximum borrowing capacity $ 20,000,000        
Committed Portion Of Credit Facility [Member] | Domestic [Member]          
Line of Credit Facility [Line Items]          
Maturity date of agreement Jul. 01, 2021        
Minimum [Member] | Domestic [Member] | Committed Line Of Credit [Member]          
Line of Credit Facility [Line Items]          
Interest rate description USD LIBOR plus 87.5 basis points        
Maximum [Member] | Domestic [Member] | Committed Line Of Credit [Member]          
Line of Credit Facility [Line Items]          
Interest rate description USD LIBOR plus 162.5 basis points