using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

         var query =  "select id, Details.Id, Details.Info.Id from DetailsItem";

        string queryResult = Regex.Replace(query, @"\bDetails\b", "[Details]", RegexOptions.None); 

        Console.WriteLine(queryResult);

    }

}