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Significant Accounting Policies - Summary of Sales Return Reserve (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Accounting Policies [Abstract]      
Beginning balance $ 29,184 $ 19,005 $ 13,198
Returns (691,953) (530,824) (385,022)
Provisions 697,873 541,003 390,829
Ending balance $ 35,104 $ 29,184 $ 19,005