Annual report pursuant to Section 13 and 15(d)

Basis of Presentation and Summary of Significant Accounting Policies - Revenue from Significant Partners (Details)

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Basis of Presentation and Summary of Significant Accounting Policies - Revenue from Significant Partners (Details) - Customer Concentration Risk - Revenue
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Partner A      
Revenue, Major Customer      
Total revenues (as a percent) 46.00% 41.00% 27.00%
Partner B      
Revenue, Major Customer      
Total revenues (as a percent) 19.00% 14.00% 23.00%
Partner C      
Revenue, Major Customer      
Total revenues (as a percent) 0.00% 0.00% 18.00%