Description of business and summary of significant accounting policies - Initial Public Offering and Reorganization Transactions (Details) $ / shares in Units, $ in Millions		6 Months Ended
	Jan. 16, 2024 USD ($) Vote LLCUnit $ / shares shares	Jun. 30, 2026 Vote
Initial Public Offering [Abstract]
Proceeds from Issuance Initial Public Offering | $	$ 172.8
Ownership interests recapitalized into LLC interests | LLCUnit	44,871,794
Class A Common Stock
Initial Public Offering [Abstract]
Number of votes per share | Vote		1
Purchase of interest in entity (in shares)	6,410,257
Acquired interest in entity, value of interest acquired | $	$ 125.2
Class A Common Stock | Smith Douglas Holdings LLC | Non- Controlling Interests
Initial Public Offering [Abstract]
LLC interests purchased (in shares)	2,435,897
Value of LLC interests purchased | $	$ 47.6
Class B Common Stock
Initial Public Offering [Abstract]
Number of votes per share | Vote		10
Maximum number of Class B common stock outstanding compared to total of Class A and Class B common stock outstanding for occurrence of sunset	10.00%
Shares issued (in shares)	42,435,897
IPO | Class A Common Stock
Initial Public Offering [Abstract]
Number of shares issued (in shares)	8,846,154
Offering price per share (in dollars per share) | $ / shares	$ 21.00
Number of votes per share | Vote	1
IPO | Class B Common Stock
Initial Public Offering [Abstract]
Number of votes per share | Vote	10
Underwriters' Option | Class A Common Stock
Initial Public Offering [Abstract]
Number of shares issued (in shares)	1,153,846