The special investigations unit of Horizon Blue Cross Blue Shield of New Jersey generated $43.2 million in savings last year by rooting out fraud, the Newark, N.J., health insurer said Wednesday.

Horizon said one of the latest trends in fraud is the "phantom doctor's office," which are shell offices that submit bogus claims using stolen insurance identification numbers and then vanish.

Another increasingly common scheme, Horizon said, is "the impossible day," on which a doctor claims to have seen dozens or even hundreds of patients.

Horizon, which had $11.5 billion in 2015 revenue, opened 988 new fraud cases last year, and referred 187 cases to the New Jersey Insurance Fraud Prosecutor, the New Jersey Attorney General's Office, the FBI, and other agencies.

hbrubaker@phillynews.comv