CONDENSED BALANCE SHEETS (Parenthetical) - $ / shares shares in Millions	Sep. 30, 2023	Dec. 31, 2022
Kirby stockholders' equity:
Common stock, par value per share (in dollars per share)	$ 0.1	$ 0.1
Common stock, shares authorized (in shares)	120.0	120.0
Common stock, shares issued (in shares)	65.5	65.5
Treasury Stock, Shares	6.2	5.6

Face amount or stated value per share of common stock.

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The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

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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.

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Number of previously issued common shares repurchased by the issuing entity and held in treasury.

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