Increase in Net Worth of Politicians While They're in Office

An article on a legislator's improbable increase in wealth during his time in office can be found here. This isn't generally used as mud-slinging ammunition, because it's true of many (most?) high-level politicians from both parties.

Is this information easily available? It would be interesting to put together a chart of everyone in Congress in terms of change over time in office of wealth, and then compare that to the average American in their same age bracket, from their home districts.