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Stock-Based Compensation - Additional Information (Detail) $ / shares in Units, $ in Millions	1 Months Ended				3 Months Ended		9 Months Ended
	Mar. 31, 2024 $ / shares shares	Mar. 31, 2023 $ / shares shares	Mar. 31, 2022 Tranche shares	May 31, 2016	Sep. 30, 2024 USD ($) $ / shares shares	Sep. 30, 2023 USD ($) $ / shares shares	Sep. 30, 2024 USD ($) $ / shares shares	Sep. 30, 2023 USD ($) $ / shares shares	Sep. 30, 2022 $ / shares shares	Jun. 30, 2024 shares	Dec. 31, 2023 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares issued					101,796,365		101,796,365				92,997,158
Weighted Average Grant Date Fair Value per Share, Granted \| $ / shares							$ 33.89
Number of Shares, Granted							3,326,772
Unvested restricted stock units					5,450,594		5,450,594				4,041,753
Risk-free interest rate					4.00%		4.20%	4.40%
Expected dividend yield					0.00%		0.00%	0.00%
Expected volatility					75.80%		76.30%	78.70%
Expected term					6 years		6 years	6 years
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining vesting period							1 year 1 month 28 days
Number of Shares, Granted						0
Weighted average grant date fair value per share \| $ / shares					$ 16.98		$ 21.21	$ 28.92
Total intrinsic value of stock options exercised \| $					$ 1.1	$ 4.8	$ 3.1	$ 6.6
Unrecognized compensation cost related to stock options \| $					$ 34.5		$ 34.5
2015 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Description of stock options granted under the Plan							Stock options generally vest as to one-third on the first anniversary of the original vesting date, with the balance vesting monthly over the remaining two years, unless they contain specific vesting provisions. The maximum term of stock options granted under the 2015 Plan and the Inducement Plan is ten years.
Shares available for future issuance					4,808,720		4,808,720
Percentage of cumulative increase in number of shares for future issuance							4.00%
2024 Inducement Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance					500,826		500,826			850,000
2016 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Description of stock options granted under the Plan				The 2016 Plan allows eligible employees to purchase shares of the Company’s common stock on the last day of each predetermined six-month offering period at 85% of the lower of the fair market value per share at the beginning or end of the applicable offering period.
Percentage of fair market value of common stock				85.00%
Shares available for future issuance					989,736		989,736
Common stock, shares issued					87,751	69,631	87,751	69,631
Weighted Average Grant Date Fair Value per Share, Granted \| $ / shares							$ 19.02	$ 29.45
Risk-free interest rate					5.37%	5.53%
Expected dividend yield					0.00%	0.00%	0.00%	0.00%
Expected volatility					59.00%	60.40%
Expected term					6 months	6 months	6 months	6 months
Service Awards [Member] \| RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining vesting period	3 years	3 years
Weighted Average Grant Date Fair Value per Share, Granted \| $ / shares	$ 32.66	$ 40.75
Number of Shares, Granted	2,157,921	2,195,135
Unvested restricted stock units					4,464,378		4,464,378
Market Awards [Member] \| RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested restricted stock units					488,555		488,555
Market Awards [Member] \| RSUs [Member] \| Senior Executives [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining vesting period							3 years	3 years	3 years
Weighted Average Grant Date Fair Value per Share, Granted \| $ / shares							$ 51.12	$ 68.55	$ 126.49
Number of Shares, Granted							286,084	181,743	55,144
Risk-free interest rate							4.28%	4.60%	1.44%
Expected dividend yield							0.00%	0.00%	0.00%
Expected volatility							77.20%	84.34%	82.53%
Expected term							3 years	3 years	3 years
Performance Based Awards with TSR Multiplier [Member] \| RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested restricted stock units					453,243		453,243
Performance Based Awards with TSR Multiplier [Member] \| RSUs [Member] \| Senior Executives [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Average Grant Date Fair Value per Share, Granted \| $ / shares							$ 36.16
Number of Shares, Granted							486,617
Risk-free interest rate							4.28%
Expected dividend yield							0.00%
Expected volatility							77.20%
Expected term							3 years
Performance Based Awards [Member] \| RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Average Grant Date Fair Value per Share, Granted \| $ / shares					$ 30.63	$ 39.14	$ 33.89	$ 42.36
Total fair value amount, Vested \| $					$ 2.8	$ 4.2	$ 38.3	$ 22.5
Unvested restricted stock units					44,418		44,418
Unrecognized equity-based compensation expense related to restricted stock \| $					$ 133.3		$ 133.3
Weighted average period of unrecognized compensation costs							1 year 8 months 12 days
Performance Based Awards [Member] \| RSUs [Member] \| Non-executive Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Granted			66,296
Number of tranches \| Tranche			2
Performance Based Awards [Member] \| First Anniversary of Original Vesting Date [Member] \| RSUs [Member] \| Non-executive Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Granted			21,878
Maximum [Member] \| 2016 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares issued					500,000		500,000
Maximum [Member] \| Performance Based Awards with TSR Multiplier [Member] \| RSUs [Member] \| Senior Executives [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Arrangements by Share Based Payment Award, Performance Shares							200.00%
TSR modifier							125.00%
Minimum [Member] \| Performance Based Awards with TSR Multiplier [Member] \| RSUs [Member] \| Senior Executives [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Arrangements by Share Based Payment Award, Performance Shares							0.00%
TSR modifier							75.00%