Alternative Minimum Tax on A Casualty

I own land that was occupied by squatters for part of 2018- until they blew up three of my buildings in a drug lab fire.  I'm not in the area and learned of it through the sheriff's department.  Once I got a copy of the Police Report I ended up compiling values of the property that was lost and the cost of cleaning up the area.  Once I entered that Turbotax told me I'd pay an AMT on the deduction- does this sound right and how is it calculated?