XML 15 R40.htm IDEA: XBRL DOCUMENT v3.19.3
Significant Accounting Policies - Concentration of Credit Risk (Details) - Institution
9 Months Ended 12 Months Ended
Sep. 30, 2019
Dec. 31, 2018
Concentration Risk [Line Items]    
Number of financial institutions where substantially all of the cash is maintained 1  
Accounts Receivable | Credit Concentration Risk    
Concentration Risk [Line Items]    
Concentration risk (as a percent) 31.00% 48.00%
Accounts Receivable | Credit Concentration Risk | Largest customer    
Concentration Risk [Line Items]    
Concentration risk (as a percent) 16.00% 25.00%
Accounts Receivable | Credit Concentration Risk | Second largest customer    
Concentration Risk [Line Items]    
Concentration risk (as a percent) 15.00% 13.00%
Accounts Receivable | Credit Concentration Risk | Third largest customer    
Concentration Risk [Line Items]    
Concentration risk (as a percent)   10.00%