Insert multiple rows with single a query from one table into another in Oracle

I have two tables, dcr_details_new and dcr_details_old where the primary key is DCRDID.

Both dcr_details_new and dcr_details_old tables share the same structure.The primary key is DCRDID where I increment by one in each insert.

I need to fetch all the rows from dcr_details_old into dcr_details_new where I have to filter the records by DOCREGNO and DCR_No

So a normal single row import/insert is running exactly as follows.

INSERT INTO dcr_details_new 
SELECT (select Max(DCRDID) + 1 from dcr_details_new),
       TWNCODE,
       '100008',
       DOCCATOGARY,
       DCR_NO,
       VISIT_NO,
       GIVEAWAY,
       COMPETITORBRN,
       REMARK,
       DCRDRDATE,
       COM_ACTI
 FROM dcr_details_old  
WHERE DOCREGNO= 'T10037'
  and DCR_NO = 28766;

1 rows created.

Now I want to skip filtering by dcr_no and insert the records as it contain too many records with different dcr_no's. Here when I filter only with DOCREGNO the select statements returns many records and when I try to loop the and insert I always mess up with the primary key as it is not incrementing as I wish.

Here is the loop I have tried and the error I'm getting.

declare
  i integer := 1;
BEGIN 
  FOR x IN (select * from dcr_details_old  WHERE DOCREGNO= 'T10037')
  LOOP
    INSERT INTO dcr_details_new (DCRDID, TWNCODE, DOCREGNO, DOCCATOGARY,
                                 DCR_NO, VISIT_NO, GIVEAWAY, COMPETITORBRN,
                                 REMARK, DCRDRDATE, COM_ACTI)
    SELECT (select Max(DCRDID) + 1 from dcr_details_new),
           TWNCODE,
           '100008',
           DOCCATOGARY,
           DCR_NO, VISIT_NO, GIVEAWAY, COMPETITORBRN,
           REMARK, DCRDRDATE, COM_ACTI
      FROM dcr_details_old;

     i := i + 1;
  END LOOP;
END;

Error:

**ERROR at line 1:
ORA-00001: unique constraint (SYS_C0061873) violated
ORA-06512: at line 5**

In this error SYS_C0061873 is the primary key DCRDID. Here in insert the value '100008' is the new docregno I have to put manually.

Any simple way to proceed? Kindly seek your assistance.