I have the following table:
\documentclass[12pt,notitlepage]{article}
\usepackage{setspace}
\usepackage{ifthen}
\usepackage{booktabs}
\usepackage{array}
\usepackage{multirow}
\usepackage{tabularx}
\usepackage{caption}
\begin{document}
\begin{table}[!h]
\captionsetup{font=bf, labelsep=period, singlelinecheck=off}
\caption{DI detection results}
{\footnotesize \onehalfspacing
\newcolumntype{W}{>{\raggedright\arraybackslash}X}
\newcolumntype{Y}{>{\raggedleft\arraybackslash}X}
\newcolumntype{Z}{>{\centering\arraybackslash}X}
\begin{tabularx}{\textwidth}{clZZZZZ}
\toprule
\multirow{2}{*}{Criterion} & \multirow{2}{*}{Statistic} & Total Period & Period 1 & Period 2 & Period 3 & Period 4\\
& & (2000--2012) & (2000--2002) & (2003--2005) & (2006--2008) & (2009--2012) \\ \otoprule
Criterion 1 & Threshold & 360.5 & 601.2 & 601.2 & 601.2 & 601.2 \\
& Detected (DI) & 32 & 31 & 64 & 31 & 12 \\
& Simultaneously detected & 18 & 15 & 34 & 6 & 5 \\
& Prop. (\%) & 56.3 & 48.4 & 53.1 & 19.4 & 41.7 \\
& & & & & & \\
Criterion 2 & Threshold & 307.4 & 514.0 & 514.0 & 514.0 & 514.0 \\
& Detected (DI) & 37 & 39 & 68 & 32 & 15 \\
& Simultaneously detected & 21 & 16 & 35 & 7 & 5 \\
& Prop. (\%) & 56.8 & 41.0 & 51.5 & 21.9 & 33.3 \\
& & & & & & \\
Criterion 3 & Threshold & 261.7 & 438.9 & 438.9 & 438.9 & 438.9 \\
& Detected (DI) & 47 & 46 & 74 & 39 & 20 \\
& Simultaneously detected & 26 & 20 & 38 & 11 & 5 \\
& Prop. (\%) & 55.3 & 43.5 & 51.4 & 28.2 & 25.0 \\
\bottomrule
\end{tabularx}}
\end{table}
\end{document}
which outputs:
However I do not like the appearance of column titles such as 'Total Period' and the year beneath it. I'd like to be able to fit "Total Period" all on one row and same with the years, e.g., (2000--2012) on one row rather than split across two. How can I do this?