left outer join with count

I have the following select:

select sj.*, sr.*, wd.doc_count from
service_jobs sj
left outer join service_receptions sr on sr.sr_id = sj.sj_sr_id
left outer join (select sj_id, count(sj_id) as doc_count from work_documents wd group by sj_id) wd on wd.wd_sj_id = sj.sj_id;

While the select works, I can't help thinking that the last join is expensive. Is there a cleaner (quicker) method of doing this?

Gary