Date Difference between consecutive rows plsql : I have a table with following structure

RetailerCode  Orderdate
714	 01-JUL-16
838	01-JUL-16
556	04-JUL-16
1003	04-JUL-16
284	01-JUL-16
1205	06-JUL-16
271	06-JUL-16
863	02-JUL-16
640	02-JUL-16
937	02-JUL-16
321	02-JUL-16
1176	06-JUL-16
998	04-JUL-16
237	05-JUL-16
1103	05-JUL-16
417	06-JUL-16
1264	07-JUL-16
462	07-JUL-16
445	07-JUL-16
913	02-JUL-16
859	02-JUL-16
196	04-JUL-16
778	05-JUL-16

i wants this type 

1001      10/9/2011 - 12/9/2011     2 days
1001      12/9/2011 - 20/9/2011     8 days
1001      20/9/2011                 NA