Rep. Brian Bilbray (R-Calif.) has conceded to Democrat Scott Peters in one of the nation's closest — and most expensive — House races.

Bilbray had trailed Peters by just a few hundred votes on election night, but that gap has now expanded to more than 3,700 votes. The San Diego-based district was a top target by both parties and saw a total of $7.3 million in independent expenditures pour in, making it one of the most expensive House races in the country.

Peters's win means Democrats netted four seats in California, half their total gains in the House.

Peters, a San Diego port commissioner, has been in Washington, D.C., this week for new-member orientation.

Bilbray's concession leaves just four seats undecided. Reps. Mike McIntyre (D-N.C.) and Ron BarberRonald (Ron) Sylvester BarberPrinciples and actions mean more than Jeff Flake’s words Giffords to lawmakers avoiding town halls: 'Have some courage' Ten House seats Dems hope Trump will tilt MORE (D-Ariz.) have narrow leads in their races, Rep. Allen West (R-Fla.) is awaiting a court decision on whether he can force a recount in a race he trails in, and Reps. Charles BoustanyCharles William BoustanyDems face hard choice for State of the Union response Americans worried about retirement should look to employee ownership Top Lobbyists 2017: Hired Guns MORE Jr. (R-La.) and Jeff Landry (R-La.) will face off in an early December runoff election.