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Stock-Based Compensation - Summary of Stock-based Compensation Expense (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Share-based Payment Arrangement [Abstract]        
Stock-based compensation expense $ 5,755 $ 6,164 $ 11,384 $ 12,073