Storage Discrepancy

I go to "about this Mac," "more info," under storage at the bottom of the page, click "storage settings."  Now the graph comes up and shows each category and how much is being used.  When I hover over documents (the largest bar in the graph), it shows that I am using 169Gb.  

I then open finder and right click on "documents," click "get info", it shows that the file size is 150Gb.  I have tried emptying the trash.  There is only one account on the apple macbook air. What gives?