How to get Check Number in After Insert Trigger on ap_checks_all

I'm using following piece of code to get the check_number in a trigger, but Im always getting -1 as the check-number

create or replace TRIGGER xx_ap_checks_trg AFTER

  INSERT ON ap_checks_all

  FOR EACH ROW

DECLARE

  lc_check_num number;

BEGIN

  lc_check_num := :new.CHECK_NUMBER;

END;