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Summary of Significant Accounting Policies - Accounts Receivable, Net (Details) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Accounts Receivable, Net    
Allowance for uncollectible receivables $ 0 $ 42,000
Accounts receivable written off 0 0
Allowance for expected sales discounts $ 8,900,000 $ 5,600,000
Revenues | Customer Concentration Risk    
Concentration risk percentage    
Concentration risk percentage 97.00%  
Revenues | Customer Concentration Risk | Customer A    
Concentration risk percentage    
Concentration risk percentage 30.00%  
Revenues | Customer Concentration Risk | Customer B    
Concentration risk percentage    
Concentration risk percentage 30.00%  
Revenues | Customer Concentration Risk | Customer C    
Concentration risk percentage    
Concentration risk percentage 37.00%  
Accounts Receivable | Customer Concentration Risk    
Concentration risk percentage    
Concentration risk percentage 96.00%  
Accounts Receivable | Customer Concentration Risk | Customer A    
Concentration risk percentage    
Concentration risk percentage 46.00%  
Accounts Receivable | Customer Concentration Risk | Customer B    
Concentration risk percentage    
Concentration risk percentage 22.00%  
Accounts Receivable | Customer Concentration Risk | Customer C    
Concentration risk percentage    
Concentration risk percentage 28.00%