Depends on what documents are on the film. Some only need to be kept 3 years, some 7 years, some 10, and some indefinitely.
For example, personnel records only need to be kept for 3 years after the employee left the company. Payment check film, is 7 years, and so on.
We store the most recent 12 months on site with a copy at a second location. All else goes into a long term storage facility. (3rd party vendor)