Stock-based Compensation - Additional Information (Details) $ / shares in Units, $ in Millions			1 Months Ended	3 Months Ended		9 Months Ended		24 Months Ended
	Jul. 02, 2020 shares	Jun. 08, 2020 USD ($) employee	Dec. 31, 2019 employee $ / shares shares	Sep. 30, 2020 USD ($) shares	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) shares	Sep. 30, 2019 USD ($)	Dec. 31, 2017 USD ($) employee	Jul. 31, 2015 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense				$ 2.7	$ 1.5	$ 7.3	$ 2.3
Proceeds from release of shares upon repayment						$ 1.3	0.0
Settlement of subscriptions receivable, number of executive employees | employee		2
2020 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (shares) | shares	5,503,678
Common stock reserved for issuance, annual increase, percentage of outstanding shares	5.00%
Maximum shares that may be issued upon exercise of incentive stock options (shares) | shares	3,650,000
Common stock available for grant (shares) | shares				5,262,053		5,262,053
Shares available for future grant, transferred from previous plan (shares) | shares	1,753,678
2020 ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (shares) | shares	1,000,000
Common stock reserved for issuance, annual increase, percentage of outstanding shares	1.00%
Number of shares available for issuance, annual increase (shares) | shares	1,000,000
2015 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (shares) | shares									7,312,590
Common stock available for grant (shares) | shares				0		0
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense				$ 2.7	1.5	$ 7.3	2.3
Repricing of stock options (shares) | shares			1,708,300
Repricing of stock options, number of employees impacted | employee			198
Repricing of stock options, exercise price, lower limit (usd per share) | $ / shares			$ 26.04
Repricing of stock options, exercise price, upper limit (usd per share) | $ / shares			28.53
Repricing of stock options, fair value (usd per share) | $ / shares			$ 23.69
Repricing of stock options, incremental expense				0.1		0.3
Repricing of stock options, unrecognized incremental expense				1.3		$ 1.3
Repricing of stock options, unrecognized incremental expense, period for recognition						1 year 1 month 6 days
Unrecognized expense				32.3		$ 32.3
Unrecognized expense, period for recognition						1 year 4 months 24 days
Stock options | 2015 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period						4 years
Expiration period						10 years
Executive | Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense				0.1	$ 0.1	$ 0.1	$ 0.1
Unrecognized expense				$ 0.1		$ 0.1
Unrecognized expense, period for recognition						7 months 6 days
Subscriptions receivable, number of executive employees | employee								2
Subscriptions receivable								$ 1.5
Subscriptions receivable, weighted average interest rate								1.90%
Proceeds from release of shares upon repayment		$ 1.3