JQuery :: How To Get ID Of Parent DIV

I am trying to get the ID of a parent. For example:
<div id="parent_holder1">
<div class="child_div">child div instance one</div>
<br /><div class="child_div">child div instance two</div>
</div><!-- PARENT HOLDER 1 -->
<br /><br />
<div id="parent_holder2">
<div class="child_div">child div instance three</div>
<br /><div class="child_div">child div instance four</div>
</div><!-- PARENT HOLDER 1 -->

When I click any of the children with a class of 'child_dev', I would like to get the ID of the parent the clicked child is within. For example - if I click "child div instance three" it would return "parent_holder2".