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Stock-based Compensation - Additional Information (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]        
Total stock-based compensation expense $ 8,761 $ 5,528 $ 25,390 $ 14,951
Capitalized website development and internal-use software costs excluded from stock-based compensation expense 324 89 950 299
Total payments for employees' tax obligations to taxing authorities due to net share settlements $ 4,192 $ 4,379 $ 12,783 $ 21,867
Class A Common Stock        
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]        
Employee tax withholding requirements and option costs due to net share settlement 120,943 93,933 345,114 565,403