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EQUITY-BASED COMPENSATION - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		6 Months Ended
	Apr. 24, 2026	Jun. 30, 2026	Apr. 27, 2026	Dec. 31, 2025
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Common stock value		37,500,000
Profits Interest Units Conversion and IPO Options Awards \| IPO Options
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share price		$ 23
Profits Interest Units Conversion and IPO Options Awards \| Vested IPO Options
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Incremental compensation cost	$ 20,200
Profits Interest Units Conversion and IPO Options Awards \| Unvested IPO Options
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Incremental compensation cost		$ 103,800
Profits Interest Units Conversion and IPO Options Awards \| IPO
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share price		$ 23
Stock Options
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Unrecognized compensation cost		$ 95,700
Weighted average recognition period		1 year 10 months 24 days
Grant period for stock		10 years
Restricted Stock Awards
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Unrecognized compensation cost		$ 23,100
Weighted average recognition period		2 years
Restricted Stock Units
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Unrecognized compensation cost		$ 9,800
Weighted average recognition period		1 year 10 months 24 days
Class A common stock
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Common stock value		$ 29		$ 0
Common stock, shares issued		287,400,000		0
Class A common stock \| IPO
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Common stock, shares issued			50,892,857
Class A common stock \| Profits Interest Units Conversion and IPO Options Awards
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share price		$ 23
Class A common stock \| Profits Interest Units Conversion and IPO Options Awards \| Granted IPO Options to Executive Officers
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Common stock, shares issued		3,500,000
Class A common stock \| Profits Interest Units Conversion and IPO Options Awards \| Granted IPO Options to X-Energy's Directors
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Common stock, shares issued		100,000
Class B common stock
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Common stock value		$ 12		$ 0
Common stock, shares issued		118,900,000		0
2026 Equity Incentive Plan \| Class A common stock
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Percentage of aggregate number of common stock share outstanding		5.00%
2026 Equity Incentive Plan \| Class B common stock
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Percentage of aggregate number of common stock share outstanding		5.00%