Stock-Based Compensation - Narrative (Details) $ / shares in Units, $ in Thousands					1 Months Ended			3 Months Ended		9 Months Ended		44 Months Ended
	Feb. 23, 2024 shares	Mar. 02, 2023 shares	Jan. 01, 2021	Jan. 01, 2020 shares	May 31, 2021 $ / shares	Nov. 30, 2020 $ / shares	May 31, 2020 tranche shares	Sep. 30, 2024 USD ($) $ / shares shares	Sep. 30, 2023 USD ($) $ / shares shares	Sep. 30, 2024 USD ($) $ / shares shares	Sep. 30, 2023 USD ($) $ / shares shares	Jun. 30, 2024 USD ($)	Dec. 31, 2023 $ / shares shares	Sep. 30, 2018 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value, grants in period (in usd per share) | $ / shares								$ 19.42	$ 24.42	$ 15.35	$ 22.39
Stock based compensation not recognized, options | $								$ 29,300		$ 29,300
Stock based compensation not recognized, period for recognition (in years)										1 year 10 months 24 days
Compensation expense | $								49,769	$ 21,819	$ 104,045	$ 66,439
Granted (in shares)										478,263
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercises in period, intrinsic value | $								$ 100	$ 200	$ 9,100	$ 900
Expected dividend yield								0.00%	0.00%	0.00%	0.00%
Shares underlying unvested restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation not recognized, period for recognition (in years)										2 years
Stock based compensation not recognized, other than options | $								$ 119,100		$ 119,100
Unvested balance (in shares)								4,965,567		4,965,567			4,346,785
Weighted average grant date fair value (in usd per share) | $ / shares								$ 32.74		$ 32.74			$ 42.63
Shares underlying unvested performance-based restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value, grants in period (in usd per share) | $ / shares					$ 148.19	$ 113.40
Stock based compensation not recognized, period for recognition (in years)										1 year 10 months 24 days
Stock based compensation not recognized, other than options | $								$ 13,900		$ 13,900
Weighted-average derivative service period					4 years	4 years
Additional service period requirement						2 years
Market-based stock unit vesting period					6 months	6 months
Weighted average grant date fair value, Vested in period (in usd per share) | $ / shares					$ 148.19	$ 113.40
Compensation expense | $								22,700	$ 800	$ 26,300	$ 1,300	$ 0
Cumulative charge | $								$ 23,500
Granted (in shares)								221,347
Total market-based restricted stock units approved and granted (in shares)										870,268
Unvested balance (in shares)								1,291,889		1,291,889			412,490
Weighted average grant date fair value (in usd per share) | $ / shares								$ 40.30		$ 40.30			$ 91.25
Shares underlying unvested performance-based restricted stock units | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average derivative service period						7 months 6 days
Market-based stock unit vesting period						7 months 6 days
Shares underlying unvested performance-based restricted stock units | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average derivative service period						4 years
Market-based stock unit vesting period						4 years 6 months
MSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Market-based restricted stock share price goal			30 days
Unvested balance (in shares)													2,260,764
Weighted average grant date fair value (in usd per share) | $ / shares													$ 65.20
MSUs | Chief Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total market-based restricted stock units approved and granted (in shares)							1,695,574
Number of tranches | tranche							3
Shares available for issuance under the 2018 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation not recognized, period for recognition (in years)										1 month 6 days
Stock based compensation not recognized, other than options | $								$ 500		$ 500
Compensation expense | $								$ 900	$ 800	$ 3,400	$ 3,800
Expected dividend yield										0.00%	0.00%
Shares authorized (in shares)	1,106,700	1,026,194		942,614
Maximum employee subscription rate, ESPP								10.00%		10.00%
Purchase price of common stock (as a percent of the fair value of common stock)										85.00%
Purchase period										6 months
Common stock issued under employee stock purchase plan (in shares)								0	0	371,826	298,781
Shares available for issuance under the 2018 Employee Stock Purchase Plan | 2018 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares approved (in share)														922,250