The ratings agency backed its investment grade 'A+' default rating and 'AA-' long-term deposits rating. The company's outlook is stable.

Fitch said the Kansas City-based bank holding company's management team has used a strategy that improves earnings while still maintaining the company's conservative operating philosophy regarding capital, liquidity and credit quality.

The ratings agency noted that UMB Financial's assets were particularly vulnerable during the long period of low interest rates and a flat to inverted yield curve. A flattening yield curve -- the result of rising short-term rates and comparatively low long-term rates -- squeezes financial institutions' net interest margin, which is the difference between when banks pay to borrow money and what they can earn when they lend it.

Fitch also cited UMB's focus on improving efficiency, the closure of unprofitable branches and its exit from underperforming businesses.

Shares of UMB Financial were unchanged in after-hours trading, after shares fell 47 cents to close at $44.36.