\documentclass[11pt]{scrartcl}% Your documentclass. I recommend something from the KOMA script class

% Necessary packages
\usepackage[T1]{fontenc}% Must be loaded for proper fontencoding when using pdfLaTeX
\usepackage[utf8]{inputenx}% For proper input encoding

% Packages for tables
\usepackage{booktabs}% Pretty tables
\usepackage{threeparttable}% For Notes below table

% Some fonts
\usepackage{libertine}% Linux Libertine, may favourite text font
% \usepackage{lmodern}% The latin modern if you prefer that type of font. The default computer modern is obsolete!
% \usepackage{mathptmx}% Times
\usepackage[euler-digits]{eulervm}% an alternative mathfont

% *****************************************************************
% siunitx
% *****************************************************************
\newcommand{\sym}[1]{\rlap{#1}} % Thanks to Joseph Wright & David Carlisle

\usepackage{siunitx}
	\sisetup{
		detect-mode,
		group-digits			= false,
		input-symbols			= ( ) [ ] - +,
		table-align-text-post	= false,
		input-signs             = ,
        }	

% Character substitution that prints brackets and the minus symbol in text mode. Thanks to David Carlisle
\def\yyy{%
  \bgroup\uccode`\~\expandafter`\string-%
  \uppercase{\egroup\edef~{\noexpand\text{\llap{\textendash}\relax}}}%
  \mathcode\expandafter`\string-"8000 }

\def\xxxl#1{%
\bgroup\uccode`\~\expandafter`\string#1%
\uppercase{\egroup\edef~{\noexpand\text{\noexpand\llap{\string#1}}}}%
\mathcode\expandafter`\string#1"8000 }

\def\xxxr#1{%
\bgroup\uccode`\~\expandafter`\string#1%
\uppercase{\egroup\edef~{\noexpand\text{\noexpand\rlap{\string#1}}}}%
\mathcode\expandafter`\string#1"8000 }

\def\textsymbols{\xxxl[\xxxr]\xxxl(\xxxr)\yyy}


% *****************************************************************
% Estout related things
% *****************************************************************
\let\estinput=\input % define a new input command so that we can still flatten the document

\newcommand{\estwide}[3]{
		\vspace{.75ex}{
			\textsymbols% Note the added command here
			\begin{tabular*}
			{\textwidth}{@{\hskip\tabcolsep\extracolsep\fill}l*{#2}{#3}}
			\toprule
			\estinput{#1}
			\bottomrule
			\addlinespace[.75ex]
			\end{tabular*}
			}
		}	

\newcommand{\estauto}[3]{
		\vspace{.75ex}{
			\textsymbols% Note the added command here
			\begin{tabular}{l*{#2}{#3}}
			\toprule
			\estinput{#1}
			\bottomrule
			\addlinespace[.75ex]
			\end{tabular}
			}
		}

% Allow line breaks with \\ in specialcells
\newcommand{\specialcell}[2][c]{%
    \begin{tabular}[#1]{@{}c@{}}#2\end{tabular}
}

% *****************************************************************
% Custom subcaptions
% *****************************************************************
% Note/Source/Text after Tables
% The new approach using threeparttables to generate notes that are the exact width of the table.
\newcommand{\Figtext}[1]{%
	\begin{tablenotes}[para,flushleft]
	\hspace{6pt}
	\hangindent=1.75em
	#1
	\end{tablenotes}
	}
\newcommand{\Fignote}[1]{\Figtext{\emph{Note:~}~#1}}
\newcommand{\Figsource}[1]{\Figtext{\emph{Source:~}~#1}}
\newcommand{\Starnote}{\Figtext{* p < 0.1, ** p < 0.05, *** p < 0.01. Standard errors in parentheses.}}% Add significance note with \starnote



 \begin{document}

\begin{table}\centering
  \begin{threeparttable}
    \caption{Table with Better Notes and Better Symbols}
    \estauto{table}{3}{S[table-format=1.2,table-column-width=20mm]}
    \Figtext{Some basic text about the table.}
    \Fignote{With `threeparttables' even long notes don't get wider than the table. The result is much more typographically pleasing.}
    \Figsource{We good the data from here.}
    \Starnote
  \end{threeparttable}
\end{table}


\end{document}