Different airports have different recommended arrival times for both domestic and international flights. I recently found this out when I arrived for a flight 60 minutes before departure time and they sticker-tagged my checked suitcase "LATE" and told me there's a chance it would not make it on the plane. These recommended times to arrive change depending on if you're checking baggage or not, or if it's a busy travel time for holidays and such.
Most airlines have a chart for when you should arrive. Here are some examples:
Southwest Airport Information
Delta Check-In Requirements