How to the fetch id of newly created entry

[eluser]Unknown[/eluser]
Hi there. I am new to using CodeIgniter but am really enjoying it's features. Can anyone please tell me how I can fetch the id of a newly inserted database entry? I am basically looking for a return similar to what I would get if I used

Code:

mysql_lastid

I am currently inserting by doing:

Code:

$this->db->insert('tablename')

But haven't been able to figure out from the documentation how I get the id back.

Thanks!
Ivar