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Equity Incentive Plans - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
	Feb. 06, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares outstanding awarded		8,099,861		8,099,861		5,107,329
Stock-based compensation expense related to vesting of anti-dilution shares		$ 5,728	$ 18,169	$ 13,957	$ 20,148
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock awards granted				0
Weighted-average period of cost expects to recognize				3 years 1 month 6 days
Unrecognized compensation costs		14,600		$ 14,600
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected dividend yield				0.00%
Weighted-average grant date fair value per share				$ 20.79
Unrecognized compensation costs		57,800		$ 57,800
Weighted-average period of cost expects to recognize				3 years
Stock-Based Compensation Expense
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average period of cost expects to recognize				1 year 2 months 12 days
Stock-based compensation expense related to vesting of anti-dilution shares		$ 5,700	$ 18,200	$ 14,000	$ 20,100
2019 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of share reserved for future issuance	5,750,000
Term of awards	10 years
Percentage of amount increase in outstanding shares	5.00%
Common stock available for issuance		2,486,308		2,486,308
Shares outstanding awarded		3,263,692		3,263,692
2019 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of share reserved for future issuance	700,000	700,000		700,000
Term of awards	10 years
Percentage of amount increase in outstanding shares	1.00%
2019 Employee Stock Purchase Plan \| Stock-Based Compensation Expense
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation costs		$ 1,700		$ 1,700
2019 Employee Stock Purchase Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase of common stock through payroll deductions, percentage	20.00%
2017 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares outstanding awarded		4,819,318		4,819,318
2017 Equity Incentive Plan \| Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock awards granted				635,155