Air carrier Captain reported while in cruise flight experiencing HYD system A and B with low readings resulting in the flight diverting to an alternate airport.

Narrative

During cruise flight upon normal scan of instrument systems we discovered that both HYD system A and B were showing lower than normal readings on quantity. We kept the HYD page up to monitor and noticed every 10-15 minutes both system A and B were dropping 1%. By the time System A reached about 70 percent we decided to contact Maintenance Control and Dispatch via radio patch. We discussed the situation at length with Maintenance Control but there were no further checklists or things they could recommend other than confirming with us that the qty should not be dropping. Aside from the issue with the HYD system; dispatch had also been keeping us updated about the situation in ZZZ regarding holding for arriving aircraft and long ground delay programs in and out of ZZZ. We had an alternate of ZZZ1 and would be landing in ZZZ with about 7000 lbs of fuel which didn't leave a lot of extra time to do any hold or further checklists if the situation with the HYD became worse. We informed dispatch of our concern of the above and began discussing a precautionary diversion. We asked dispatch what would be preferable and that we had time to work out the best option being that we were not critical at the moment. ZZZ2 was the ultimate decision given our proximity to it and availability of other aircraft to swap to for our passengers. We began to set everything up for the diversion; did a briefing with the Flight Attendants; made appropriate passenger announcements and then [requested priority handling] with ATC. We were routed direct to ZZZ2 at that time. We also coordinated enough early descent into ZZZ2 so that we could burn off excess gas in order to avoid an overweight landing in ZZZ2. During all this the HYD continued to decrease until we began putting flaps and gear out for our arrival. Upon landing the indications rose again to the high 70's - low 80's in qty. We made an uneventful landing in ZZZ2 and performed a maintenance writeup regarding the hydraulic system.