Actual Capital Amounts as well as Required and Well-Capitalized Common Equity Tier One, Tier One, Total and Tier One Leverage Ratios (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 Capital, Actual Ratio	12.95%
Tier 1 Capital For Capital Adequacy Purposes, Ratio	6.00%
Tier 1 Capital To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	8.00%
Total Capital, Actual Ratio	14.04%
Total Capital For Capital Adequacy Purposes, Ratio	8.00%
Total Capital To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	10.00%
Tier 1 Leverage, Actual Ratio	9.94%
Tier 1 Leverage for Capital Adequacy Purposes, Ratio	4.00%
Tier 1 Leverage To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	5.00%
Common Equity Tier One Capital [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 Capital, Actual Ratio	12.95%
Tier 1 Capital For Capital Adequacy Purposes, Ratio	4.50%
Tier 1 Capital To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	6.50%
UMB Financial Corporation [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 Capital, Actual Amount	$ 2,041,504	$ 1,789,581
Tier 1 Capital, Actual Ratio	12.95%	11.80%
Tier 1 Capital For Capital Adequacy Purposes, Amount	$ 945,746	$ 909,903
Tier 1 Capital For Capital Adequacy Purposes, Ratio	6.00%	6.00%
Total Capital, Actual Amount	$ 2,213,050	$ 1,951,078
Total Capital, Actual Ratio	14.04%	12.87%
Total Capital For Capital Adequacy Purposes, Amount	$ 1,260,994	$ 1,213,205
Total Capital For Capital Adequacy Purposes, Ratio	8.00%	8.00%
Tier 1 Leverage, Actual Amount	$ 2,041,504	$ 1,789,581
Tier 1 Leverage, Actual Ratio	9.94%	9.09%
Tier 1 Leverage For Capital Adequacy Purposes, Amount	$ 821,527	$ 787,604
Tier 1 Leverage for Capital Adequacy Purposes, Ratio	4.00%	4.00%
UMB Financial Corporation [Member] | Common Equity Tier One Capital [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 Capital, Actual Amount	$ 2,041,504	$ 1,789,581
Tier 1 Capital, Actual Ratio	12.95%	11.80%
Tier 1 Capital For Capital Adequacy Purposes, Amount	$ 709,309	$ 682,428
Tier 1 Capital For Capital Adequacy Purposes, Ratio	4.50%	4.50%
UMB Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 Capital, Actual Amount	$ 1,750,297	$ 1,613,024
Tier 1 Capital, Actual Ratio	11.19%	10.73%
Tier 1 Capital For Capital Adequacy Purposes, Amount	$ 938,750	$ 901,809
Tier 1 Capital For Capital Adequacy Purposes, Ratio	6.00%	6.00%
Tier 1 Capital To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 1,251,666	$ 1,202,412
Tier 1 Capital To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	8.00%	8.00%
Total Capital, Actual Amount	$ 1,853,558	$ 1,707,265
Total Capital, Actual Ratio	11.85%	11.36%
Total Capital For Capital Adequacy Purposes, Amount	$ 1,251,666	$ 1,202,412
Total Capital For Capital Adequacy Purposes, Ratio	8.00%	8.00%
Total Capital To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 1,564,583	$ 1,503,016
Total Capital To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	10.00%	10.00%
Tier 1 Leverage, Actual Amount	$ 1,750,297	$ 1,613,024
Tier 1 Leverage, Actual Ratio	8.57%	8.24%
Tier 1 Leverage For Capital Adequacy Purposes, Amount	$ 816,859	$ 782,638
Tier 1 Leverage for Capital Adequacy Purposes, Ratio	4.00%	4.00%
Tier 1 Leverage To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 1,021,073	$ 978,297
Tier 1 Leverage To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	5.00%	5.00%
UMB Bank [Member] | Common Equity Tier One Capital [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 Capital, Actual Amount	$ 1,750,297	$ 1,613,024
Tier 1 Capital, Actual Ratio	11.19%	10.73%
Tier 1 Capital For Capital Adequacy Purposes, Amount	$ 704,062	$ 676,357
Tier 1 Capital For Capital Adequacy Purposes, Ratio	4.50%	4.50%
Tier 1 Capital To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 1,016,979	$ 976,960
Tier 1 Capital To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	6.50%	6.50%