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Revenue Recognition (Narrative) (Details) - USD ($)
3 Months Ended
Jan. 01, 2018
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Revenue from Contract with Customer [Line Items]        
Revenues from contract with customer   $ 6,867,000 $ 6,069,000  
Accounts receivable, net   4,138,000   $ 4,528,000
Revenue recognized related to contract liabilities   762,000    
Remaining performance obligation   $ 2,300,000    
Percentage of remaining performance obligation   74.00%    
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]        
Revenue from Contract with Customer [Line Items]        
Revenues from contract with customer $ 0      
Minimum [Member]        
Revenue from Contract with Customer [Line Items]        
Accounts receivable, balance due   30 days    
Maximum [Member]        
Revenue from Contract with Customer [Line Items]        
Accounts receivable, balance due   60 days