At some airports, from the gate area you see a herd of passengers walking behind a wall of glass. They are an international arrival and the glassed in corridor will lead to immigration and customs.

In many airports, including DTW, only certain gates are designed to handle international arrivals.[At DTW, they're some of the gates near the center of the A concourse for DL and SkyTeam flights. These gates also are designed for large wide body aircraft, so most international departures leave from this area too, roughly between A30 and A50 or so, where A38-A40 would be about the center of the terminal.] If such gates are scarce, the aircraft may be towed to another gate or even towed to a remote stand to park after everyone has deplaned.