If I have a template class, can I determine if the templated object has an overload of operator<<(std::ostream&)?

Question

Is it possible to substitute something in the dots to ensure this function is complete? I'd like to use this in something I'm developing, but I'm not sure how I can determine if a thing is printable without knowing what kind of things I might get.

template<typename U>
RunSomething(T& a1)
{
if(...)
    {
       std::cout << a1 << std::endl;
    }
}