In an Escrow account to pay property taxes, how much can they hold in reserve?

Our loan required us to have an escrow account for our property taxes and, at closing, we funded a large chunk of change. Now that they've paid the first installment for the 2008-09 fiscal year, it's obvious, they have a reserve that more than covers the entire amount for an entire year's worth of property tax. Can someone tell me how much reserve they can legally hold on to? I've searched all over the web but I haven't found any guidance.