Question: What are the dates for the documents with both 'GV' type and 'SF' type expenses?
SQL: SELECT T1.document_date FROM Documents AS T1 JOIN Documents_with_Expenses AS T2 ON T1.document_id  =  T2.document_id WHERE T2.budget_type_code  =  'GV' INTERSECT SELECT T1.document_date FROM Documents AS T1 JOIN Documents_with_Expenses AS T2 ON T1.document_id  =  T2.document_id WHERE T2.budget_type_code  =  'SF'