How Long are FBI Directors Usually in Office?

I spun up a quick chart in Tableau Public to display the tenure of various Directors of the Bureau since its inception as the “Bureau of Investigation” in 1908. Click the chart to see the interactive version on the Tableau Public website. You can mouseover data to learn more about the arrival and departure of various directors on the Tableau Public site here.

Data is from the Wikipedia article “Director of the Federal Bureau of Investigation”, retrieved May 11, 2017.