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 Ref_Shipping_Agents ( document_id VARCHAR, document_status_code VARCHAR, document_type_code VARCHAR )
TABLE: CREATE TABLE Documents ( document_id VARCHAR, document_status_code VARCHAR, document_type_code VARCHAR )

### Question ###
List the document ids of documents with the status done and type Paper, which not shipped by the shipping agent named USPS.

### Accurate SQL ###

SELECT document_id FROM Documents WHERE document_status_code = "done" AND document_type_code = "Paper" EXCEPT SELECT document_id FROM Documents JOIN Ref_Shipping_Agents ON Documents.shipping_agent_code = Ref_Shipping_Agents.shipping_agent_code WHERE Ref_Shipping_Agents.shipping_agent_name = "USPS"