Stock-Based Incentive Compensation Plans - Narrative (Details) $ in Thousands	3 Months Ended			4 Months Ended	8 Months Ended	9 Months Ended
	Jun. 30, 2021 USD ($)	Sep. 30, 2020 shares	Jun. 30, 2020 USD ($)	Apr. 30, 2020	Dec. 31, 2020 USD ($) purchase_period shares	Sep. 30, 2021 USD ($) shares	Sep. 30, 2020 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, stock options						$ 1,700
Stock options granted (in shares) | shares		0				0
Early exercise of stock options, share subject to repurchase (in shares) | shares					5,836	0
Issuance of common stock related to employee stock purchase plan	$ 1,566		$ 991
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, expected period for recognition (in years)						1 year 2 months 12 days
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, expected period for recognition (in years)						2 years 10 months 24 days
Unrecognized compensation cost						$ 34,400
2018 ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Purchase price of common stock as a percent of fair market value (percent)						85.00%
Employee stock purchase program offering period interval (in months)				6 months	12 months
Number of purchase periods in offering interval | purchase_period					2
Issuance of common stock related to employee stock purchase plan (in shares) | shares						104,861	74,685
Issuance of common stock related to employee stock purchase plan						$ 1,600	$ 1,000
Accrued compensation and related expenses for employee payroll deductions					$ 400	$ 700