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Summary of Significant Accounting Policies - Accounts Receivable (Details) - USD ($)
Jul. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Concentration Risk [Line Items]      
Allowance for doubtful accounts $ 0 $ 0 $ 0
Accounts Receivable | Customer Concentration Risk | SWK Funding LLC      
Concentration Risk [Line Items]      
Percent of revenue recognized 100.00%