A highly accessible overview of Western philosophy, from the Greeks to present day, can be found in Frederick Copleston's 9-volume "A History of Philosophy" series.

Vol 1, as sold on Amazon: http://www.amazon.com/History-Philosophy-Vol-Pre-Socratics-P...

A sharp person with a high school education, and a willingness to lookup terms or references s/he doesn't understand (with the help of Google, Wikipedia, etc.), would be able to readily digest these books, though even postdocs would find much in them that is challenging and intriguing.