Additional Paid in Capitals.

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- Definition

Amount of principal stockholders tax receivable agreement.

+ References

No definition available.

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- Definition

Amount of tax receivable agreement.

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No definition available.

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- Definition

Current prepaid expense and other assets.

+ References

No definition available.

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- Definition

Non controlling interest.

+ References

No definition available.

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- Definition

Noncurrent liabilities.

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No definition available.

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- Definition

Percentage of economic interest held by principal stockholder.

+ References

No definition available.

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- Definition

Percentage of ownership interest held by parent.

+ References

No definition available.

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- Definition

Percentage of payment by principal stockholders.

+ References

No definition available.

+ Details

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- Definition

Proceeds from shareholder loan.

+ References

No definition available.

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Balance Type:	debit
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- Definition

Repayments of shareholder loan.

+ References

No definition available.

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Balance Type:	credit
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- Definition

State corporate tax rate.

+ References

No definition available.

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Balance Type:	na
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- References

No definition available.

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- Definition

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

Face amount or stated value per share of common stock.

+ References

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- Definition

Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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- Definition

Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 740
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-Name Accounting Standards Codification
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- Definition

The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

+ References

No definition available.

+ Details

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- Definition

The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

+ References

No definition available.

+ Details

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- Definition

Amount of expense for cost associated with issuance of security by investment company. Includes, but is not limited to, legal fee pertaining to share offered for sale, registration fee, underwriting, printing prospectus, and initial fee for listing on exchange.

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- Definition

The cash inflow associated with the amount received from entity's first offering of stock to the public.

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- Definition

Per share or per unit amount of equity securities issued.

+ References

No definition available.

+ Details

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Notes to unaudited pro forma consolidated balance sheet - Additional Information (Details) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2026 USD ($)	Jun. 30, 2026 USD ($)	Dec. 31, 2025 USD ($)	May 05, 2026 $ / shares	Apr. 02, 2026 $ / shares	Dec. 31, 2025 € / shares	Dec. 31, 2025 USD ($) $ / shares shares	Dec. 31, 2024 $ / shares shares	Apr. 29, 2024 $ / shares
Unaudited Pro Forma Consolidated Balance Sheet [Line Items]
Share-based payment arrangement, expense	$ 22.8	$ 22.8
HMH Holding Inc. [Member]
Unaudited Pro Forma Consolidated Balance Sheet [Line Items]
Common stock, shares issued (in shares) \| shares							1,000	1,000
Common stock, par value (in usd per share) \| $ / shares							$ 0.01	$ 0.01	$ 0.01
HMH Holding Inc. [Member] \| Pro Forma [Member]
Unaudited Pro Forma Consolidated Balance Sheet [Line Items]
Prepaids and other current assets							$ 21.3
Common stock, shares issued (in shares) \| shares							200
Percentage of ownership interest held by parent							24.40%
Common stock, par value (in usd per share) \| € / shares						€ 1
Non-controlling interests							$ 528.1
Percentage of economic interest held by principal stockholder							75.60%
Percentage of payment by principal stockholders							85.00%
Amount of tax receivable agreement							$ 3.4
Amount of principal stockholders tax receivable agreement							5.5
Deferred tax asset							42.9
Liabilities, Noncurrent							$ 33.0
Shares issued, price per share \| $ / shares							$ 20
State corporate tax rate							25.00%
Offering cost, expense			$ 223.4
Repayments of shareholder loan			146.6
Proceeds from shareholder loan			9.5
Share-based payment arrangement, expense			21.2
HMH Holding Inc. [Member] \| Pro Forma [Member] \| Company and Non controlling Interests [Member]
Unaudited Pro Forma Consolidated Balance Sheet [Line Items]
Ownership percentage							24.40%
Equity interest percentage							75.60%
HMH Holding Inc. [Member] \| Pro Forma [Member] \| IPO [Member]
Unaudited Pro Forma Consolidated Balance Sheet [Line Items]
Proceeds from Issuance Initial Public Offering			$ 193.8
HMH Holding Inc. [Member] \| Pro Forma [Member] \| Minimum [Member]
Unaudited Pro Forma Consolidated Balance Sheet [Line Items]
Additional paid-in capital							$ 3.4
HMH Holding Inc. [Member] \| Pro Forma [Member] \| Additional Paid-in Capital [Member]
Unaudited Pro Forma Consolidated Balance Sheet [Line Items]
Additional paid-in capital							$ 528.4
Common Class B [Member]
Unaudited Pro Forma Consolidated Balance Sheet [Line Items]
Common stock, par value (in usd per share) \| $ / shares				$ 0.01	$ 0.01
Common Class B [Member] \| HMH Holding Inc. [Member] \| Pro Forma [Member]
Unaudited Pro Forma Consolidated Balance Sheet [Line Items]
Common stock, par value (in usd per share) \| $ / shares							$ 0.01
Common Class A [Member]
Unaudited Pro Forma Consolidated Balance Sheet [Line Items]
Common stock, par value (in usd per share) \| $ / shares					$ 0.01
Common Class A [Member] \| HMH Holding Inc. [Member] \| Pro Forma [Member]
Unaudited Pro Forma Consolidated Balance Sheet [Line Items]
Common stock, shares issued (in shares) \| shares							902,504
Common stock, par value (in usd per share) \| $ / shares							$ 0.01