Maximum length of stay outside US on OPT

Hello,

I graduated with a masters in May 2012 and my OPT is valid until July 2013. I worked on my opt for a month after which due to a family emergency I came to India on 27 Aug. I plan to travel back to US on Dec 15. Would a job offer letter alongwith my passport, and I- 20 be sufficient for my re-entry?