No problem in doing that. Once the phone reaches 100%, it won't draw any current until the battery goes down by a reasonable amount. I leave mine on charge overnight too.

 

There's a really cool app called Battery Monitor Widget in the play store. Here's a screenshot of HISTORY log of my battery for a period of time. You can follow along as it gets charged starting from the bottom and working your way up.

There's a percentage column as well as a mV column, battery temperature, and the one that I'd most want to point out to you is the current being drawn (mA). As you can see, as it approaches 100%, the current starts to drop, and once at 100%, it draws like 1 mA until unplugged.