ID jump from #300 to #1000 ?

Hi!
I’m using MODx for my site for a while.... and everything works fine and I’m learning alot on the way... but recently happened something wierd....
..my document ID’s were on cca. #300 and after writing some new news it "jumped" to ID #1000 and increasing? What is the reason for that? Must I be worried for that and how to repair it (if it is needed)?