oracle left outer joins not showing right null values

i'm having an issue with creating a query in oracle which doesnt seem to want to join on missing values

the table i have is this:

table myTable(refnum, contid, type)

values are:
1, 10, 90000
2, 20, 90000
3, 30, 90000
4, 20, 10000
5, 30, 10000
6, 10, 20000
7, 20, 20000
8, 30, 20000

a break down of the fields i'm after is this:

select a.refnum from myTable a where type = 90000
select b.refnum from myTable b where type = 10000 and contid in (select contid from myTable where type = 90000)
select c.refnum from myTable c where type = 20000 and contid in (select contid from myTable where type = 90000)

the outcome of the query i'm after is this:

a.refnum, b.refnum, c.refnum

i thought this would work:

select a.refnum, b.refnum, c.refnum
from myTable a 
left outer join myTable b on (a.contid = b.contid) 
left outer join myTable c on (a.contid = c.contid) 
where a.id_tp_cd = 90000
and b.id_tp_cd = 10000
and c.id_tp_cd = 20000

so the values should be:

1, null, 6
2, 4, 7
3, 5, 8

but its only returning:

2, 4, 7
3, 5, 8

i thought left joins would show all values in the left and create a null for the right.

help :(