Stock-Based Compensation - Narrative (Details) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended		12 Months Ended
	Jul. 25, 2025 USD ($) $ / shares shares	Sep. 30, 2025 USD ($) shares	Sep. 30, 2024 USD ($)	Sep. 30, 2025 USD ($) shares	Sep. 30, 2024 USD ($)	Mar. 31, 2021
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Minimum multiple realized on invested capital upon change in control						2.0
Stock-based compensation expense		$ 31,076	$ 0	$ 31,076	$ 0
Number of shares authorized for issuance (in shares) \| shares		15,500,000		15,500,000
Stock options granted (in shares) \| shares	400,960
Exercise price for options granted (in dollars per share) \| $ / shares	$ 17.00
2021 Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Unrecognized compensation cost for stock options		$ 5,202		$ 5,202
Stock Options
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Award expiration period	10 years
Stock Options \| 2021 Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Stock-based compensation expense		30,034		$ 30,034
Unrecognized compensation cost, period for recognition				8 months 12 days
Stock Options \| 2025 Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Stock-based compensation expense		939		$ 939
Unrecognized compensation cost for stock options		1,460		$ 1,460
Unrecognized compensation cost, period for recognition				3 years 2 months 12 days
Service-Based Stock Options
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Award vesting period	5 years					5 years
Service and Market-Based Stock Options
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Minimum multiple realized on invested capital upon change in control	2.0
Restricted Stock Units (RSUs)
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Award vesting period	1 year
Stock-based compensation expense		103		$ 103
Unrecognized compensation cost, period for recognition				9 months 18 days
Award granted (in shares) \| shares	32,646
Aggregate grant date fair value of awards granted	$ 555
Grant date fair value of awards granted (in dollars per share) \| $ / shares	$ 17.00
Unrecognized compensation cost for non-option awards		$ 452		$ 452

McGraw Hill, Inc. 10-Q