B737 First Officer reported a forward flight deck inner window pane failed during cruise. Flight crew diverted and landed safely.

Narrative

At FL280 in cruise as Pilot monitoring I noticed what appeared to be a ft long crack in the R1 Windshield. Upon further inspection and running my hand over the 1ft long area I realized it was an actual crack in the inner pane of the windshield. I alerted the Captain and asked him to confirm my suspicion and he agreed it was a crack also. At that point the captain gave me control of the plane so he could run the QRH. I put on my shoulder harnesses as a precaution and engaged with the Captain as he ran the QRH. Since the QRH had us don oxygen masks until the cabin was 2 PSI or less and being the inner pane is structural for the window. After defending to relieve the cabin pressure to 2.0 or less at 14000 we removed our oxygen masks and prepared for a diversion. The Captain worked with Dispatch and came to the final decision that ZZZ was the best suitable diversion airport. We received routing from ATC; and adjusted our altitude and airspeed the remaining way in an effort to avoid an overweight landing. However we had already been planning on being potentially heavy at our original destination and our efforts to get under MLW wasn't going to happen without delaying landing so we just opted for an overweight landing on ZZZ longest runway which was a non event.