As further clarification, if you want to use Quik Reports, you would select only rental lines by using the field from Contract Details, where Line Type = "Rental".

The only other possibility and it would only work if you do not use the "Sell-off" feature, would be to use 2 contract numbers - one for rentals and the other for all other line types, though it might be too clumsy. Unfortunately, there is no simply way to do it.