E145 First Officer reported the nose landing gear door had opened during cruise. The flight crew diverted; lowered the gear and landed safely.

Narrative

We departed from ZZZ to ZZZ1 on Aircraft X. It was both the first flight of the day for us the crew and the airplane. After being deiced; we departed Runway XX with a right turn to ZZZ2. After we had reached FL 250 and around 310 kts.; we turned right for the next fix and that's when we heard a loud bang. We checked the EICAS and we had no indications. FA (Flight Attendant) called us to ask if everything was alright and we told her we are trying to figure it out and we will get back to her. CA (Captain) reduces the power to slow to 250 kts. and asked me to run the nose gear door open QRH procedure. After discussing our options amongst each other and dispatch; we decided to divert to ZZZ2. We had an extra 600lbs-ish of gas above our new landing gas and asked to do a low pass over Runway XY to see if Tower could determine if the door/gear was down. They confirmed that the nose gear door was open. Once we were in the downwind again; I put the gear down to see what indications we would receive. Since we got the three green down indication; CA and myself felt comfortable attempting a landing. We had asked for the fire department to standby and that we will be stopping on the Runway. Once we had stopped and determined that we had steering and the fire department looked at our gear; we determined it was safe to taxi to the terminal.