Insurance quote 20% higher than last time last year - Iowa - any ideas?

[Matthew Gunderson]

I own a multi-use building on main street in Mount Vernon, Iowa, 2 story with retail on first floor (restaurant) and two apartments upstairs.  Built in 1890.   Last year I paid $3,258. This year they are quoting me a 20% increase at $3927.  I had budgeted a 10% increase but never expected anything like a 20% increase.  I work with a broker but am open to looking for a different broker as they only work with a handful of insurance companies - including Auto Owners.  

Any ideas?