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.
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.
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.