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Organization and Description of Business - Additional Information (Details) $ / shares in Units, $ in Millions					3 Months Ended
	Dec. 12, 2025 USD ($) shares	Dec. 12, 2025 shares	Dec. 11, 2025 $ / shares shares	Dec. 10, 2025 $ / shares shares	Mar. 31, 2026 USD ($) $ / shares shares	Dec. 31, 2025 $ / shares shares
Organization And Description Of Business [Line Items]
Preferred stock, shares authorized					10,000,000	10,000,000
Preferred stock, par value \| $ / shares					$ 0.0001	$ 0.0001
IPO
Organization And Description Of Business [Line Items]
Gross proceeds from IPO \| $	$ 277.7
Limited liability company units, issued	14,943,750	14,943,750
Net proceeds from the IPO \| $	$ 252.3
Class A Common Stock
Organization And Description Of Business [Line Items]
Common stock, par value per share \| $ / shares					$ 0.0001	$ 0.0001
Common stock, shares outstanding					15,292,984	14,947,318
Common stock voting rights					Each share of Class A Common Stock entitles its holder to one vote per share on all matters presented to Cardinal Infrastructure Group Inc.’s stockholders.
Class A Common Stock \| IPO
Organization And Description Of Business [Line Items]
Number of shares sold		1,725,000	11,500,000
Common stock, par value per share \| $ / shares			$ 0.0001
Offering price \| $ / shares			$ 21
Class B Common Stock
Organization And Description Of Business [Line Items]
Common stock, par value per share \| $ / shares					$ 0.0001	$ 0.0001
Common stock, shares outstanding					27,573,875	23,387,813
Common stock voting rights					Each share of Class B Common Stock entitles its holder to one vote per share on all matters presented to Cardinal Infrastructure Group Inc.’s stockholders.
Class B Common Stock \| IPO
Organization And Description Of Business [Line Items]
Number of shares sold	23,387,813
OpCo
Organization And Description Of Business [Line Items]
LLC Units					42,866,859	38,335,131
Ownership interest, percentage					100.00%	100.00%
Economic interest percentage of continuing equity holders					100.00%
OpCo \| Cardinal Infrastructure Group Inc.
Organization And Description Of Business [Line Items]
LLC Units					15,292,984	14,947,318
Ownership interest, percentage					35.68%	39.00%
OpCo \| Cardinal Infrastructure Group Inc. \| Class A Common Stock
Organization And Description Of Business [Line Items]
Stock split ratio					1
Cardinal Civil Contracting NC LLC \| Cardinal NC
Organization And Description Of Business [Line Items]
Ownership interest, percentage					100.00%
Continuing Equity Holders
Organization And Description Of Business [Line Items]
Economic interest percentage of continuing equity holders					61.00%
Continuing Equity Holders \| IPO
Organization And Description Of Business [Line Items]
Repayment of borrowings outstanding \| $					$ 24.3
Limited liability company units, issued	7,500,000	7,500,000
Net proceeds from the IPO \| $	$ 157.5
IPO Reorganization
Organization And Description Of Business [Line Items]
Common stock voting rights					Class A Common Stock and Class B Common Stock, each entitling the holder to one vote per share on all matters presented to stockholders
Preferred stock, shares authorized				10,000,000
Preferred stock, par value \| $ / shares				$ 0.0001
IPO Reorganization \| Class A Common Stock
Organization And Description Of Business [Line Items]
Common stock, shares outstanding				1,718,750
Stock split					86-to-one forward stock split
Stock split ratio				86
IPO Reorganization \| Class B Common Stock
Organization And Description Of Business [Line Items]
Number of shares sold				23,387,813
IPO Reorganization \| Continuing Equity Holders
Organization And Description Of Business [Line Items]
Economic interest percentage of continuing equity holders				61.00%