How do I document a moving bonus that I had to repay an ex-employer?

In 2015, I was paid a moving/hiring bonus when I started a new job. However, I left the job in 2016 and had to repay half of that. How do I put that amount in my taxes as that was sent in a check directly to my ex-employer? (My ex-employer told me I don't have to file an amended return for 2015 but I can't find the letter they sent me.)