idle temps are normally around 40-45degrees. This varies some depending on the size and airflow of your case. also on room temperatures
if you're in an air conditioned room (about 70degrees) - then 48 is high. Since it's summer, if you're room temps are warmer, then 48 is ok.
All in all... since it's a $300 processor... i'd reccomend picking up some thermal grease. Either at your local shop, or ordering Arctic Silver 5 on newegg for $10bucks (gives you 5 to 7 applications for a $10 tube)
It alone will lower your temps across the board by about 5degrees