String Concatenation:
$("#" + this.id + "_div").offset().top
Note that there is no need to create unique IDs, DOM duo to having tree-like structure provides many different methods for traversing and selecting the target elements.
Since you are generating the elements dynamically you should also delegate the events, you can add classes to your elements and use the on
method:
$('#aStaticParentElement').on('click', '.anchors', function() {
// TODO:
// select the target element either by traversing
// or by using an identifier
});