  Let $D(n)$ be the maximal determinant for $n \times n$ $\{\pm 1\}$-matrices,
and ${\mathcal R}(n) = D(n)/n^{n/2}$ be the ratio of $D(n)$ to the Hadamard
upper bound. We give several new lower bounds on ${\mathcal R}(n)$ in terms of
$d$, where $n = h+d$, $h$ is the order of a Hadamard matrix, and $h$ is maximal
subject to $h \le n$. A relatively simple bound is \[{\mathcal R}(n) \ge
\left(\frac{2}{\pi e}\right)^{d/2}
  \left(1 - d^2\left(\frac{\pi}{2h}\right)^{1/2}\right)
  \;\text{ for all }\; n \ge 1.\] An asymptotically sharper bound is
\[{\mathcal R}(n) \ge \left(\frac{2}{\pi e}\right)^{d/2}
  \exp\left(d\left(\frac{\pi}{2h}\right)^{1/2} +
  \; O\left(\frac{d^{5/3}}{h^{2/3}}\right)\right).\] We also show that
\[{\mathcal R}(n) \ge \left(\frac{2}{\pi e}\right)^{d/2}\] if $n \ge n_0$ and
$n_0$ is sufficiently large, the threshold $n_0$ being independent of $d$, or
for all $n\ge 1$ if $0 \le d \le 3$ (which would follow from the Hadamard
conjecture). The proofs depend on the probabilistic method, and generalise
previous results that were restricted to the cases $d=0$ and $d=1$.
