sql - pl sqlトリガーはシーケンスから値を挿入します

Question

create table userdetail(
  userdetailsid number(3) not null,
  userid varchar2(5),
  firstname varchar2(15),
  lastname varchar2(15),
  email varchar2(15),
  primary key (userdetailsid)
);

create sequence Iseq
start with 1
increment by 1;

create or replace trigger userDetailInsert
before insert on userdetail
begin
  :userdetailsid:=Iseq.nextval;
end;

私が得るエラーは次のとおりです。

Error at line 2: PLS-00049: bad bind variable 'USERDETAILSID'