If $A=\begin{bmatrix}\sqrt2&1\\-1&\sqrt2\end{bmatrix}$, $B=\begin{bmatrix}1&0\\1&1\end{bmatrix}$, $C=ABA^{\mathrm T}$ and $X=A^{\mathrm T}C^{2}A$, then $\det X$ is equal to: