Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE Documents_with_expenses (document_id VARCHAR, budget_type_code VARCHAR)

### Question ###
What are the document ids for the budget type code 'SF'?

### Accurate SQL ###

SELECT document_id FROM Documents_with_expenses WHERE budget_type_code = 'SF'