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Equity Incentive Plans - Summary of Share-based Awards Available for Grant under 2016 Plan (Details) - 2016 Plan - shares
9 Months Ended 12 Months Ended
Sep. 30, 2019
Dec. 31, 2018
Share-Based Awards Available For Grant    
Beginning balance 4,717,292 4,034,152
Additional awards authorized 1,218,402 1,168,865
Awards granted (620,624) (666,913)
Awards forfeited 155,253 124,478
Awards withheld for tax purposes 58,341 56,710
Ending balance 5,528,664 4,717,292