I'm a licensed insurance agent...
Couple things to be aware of:
1) Musical Instruments generally need to be added to a homeowner's or renter's policy with a 'musical instrument floater'. Here you'll itemize the instruments you want protected, less the deductible amount of your choosing. You'll need to validate the value as mentioned above, and the items will be assumed to be replaced with actual cash value - not full replacement value. You can opt for replacement (new) value, but it will cost much more and you'll need to prove the worth, etc. This is very similar to a 'jewelry floater' for wedding rings, high-end watches, etc.
2) An important note: Unlike the jewelry floater, if you remove the instrument from your residence (band practice facility, church band, any show, venue, etc) to play it, the floater will be suspended or canceled. That's great isn't it? Generally, unless you play at home in your bedroom - always - the musical instrument floater is worthless. It's great for people with kick-butt collections though.
Now, this is Ohio insurance law, and every state's insurance commission regulations will differ slightly. Yours might be different. With instruments, the best insurance is vigilance and keeping them locked and out of sight when not in use.