Regulatory Matters (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Enterprise Financial Services Corp [Member]
Total Capital (to Risk Weighted Assets) [Abstract]
Actual, Amount	$ 589,047	$ 506,349
Actual, Ratio	12.21%	13.48%
For Capital Adequacy Purposes, Amount	$ 385,816	$ 300,573
For Capital Adequacy Purposes, Ratio	8.00%	8.00%
To Be Well Capitalized Under Applicable Action Provisions, Amount	$ 0	$ 0
To Be Well Capitalized Under Applicable Action Provisions, Ratio	0.00%	0.00%
Tier 1 Capital (to Risk Weighted Assets) [Abstract]
Actual, Amount	$ 496,045	$ 412,865
Actual, Ratio	10.29%	10.99%
For Capital Adequacy Purposes, Amount	$ 289,362	$ 225,430
For Capital Adequacy Purposes, Ratio	6.00%	6.00%
To Be Well Capitalized Under Applicable Action Provisions, Amount	$ 0	$ 0
To Be Well Capitalized Under Applicable Action Provisions, Ratio	0.00%	0.00%
Tier One Common Equity Capital	$ 428,397	$ 357,729
Tier One Common Equity Capital to Risk Weighted Assets	8.88%	9.52%
Tier One Common Equity Capital Required for Capital Adequacy	$ 217,021	$ 169,072
Tier One Common Equity Capital Required for Capital Adequacy to Risk Weighted Assets	4.50%	4.50%
Tier One Common Equity Capital Required to be Well Capitalized	$ 0	$ 0
Tier One Common Equity Capital Required to be Well Capitalized to Risk Weighted Assets	0.00%	0.00%
Tier 1 Capital (to Average Assets) [Abstract]
Actual, Amount	$ 496,045	$ 412,865
Actual, Ratio	9.72%	10.42%
For Capital Adequacy Purposes, Amount	$ 204,087	$ 158,480
For Capital Adequacy Purposes, Ratio	4.00%	4.00%
To Be Well Capitalized Under Applicable Action Provisions, Amount	$ 0	$ 0
To Be Well Capitalized Under Applicable Action Provisions, Ratio	0.00%	0.00%
Enterprise Bank and Trust [Member]
Total Capital (to Risk Weighted Assets) [Abstract]
Actual, Amount	$ 546,314	$ 430,981
Actual, Ratio	11.36%	11.53%
For Capital Adequacy Purposes, Amount	$ 384,791	$ 298,982
For Capital Adequacy Purposes, Ratio	8.00%	8.00%
To Be Well Capitalized Under Applicable Action Provisions, Amount	$ 480,989	$ 373,728
To Be Well Capitalized Under Applicable Action Provisions, Ratio	10.00%	10.00%
Tier 1 Capital (to Risk Weighted Assets) [Abstract]
Actual, Amount	$ 503,312	$ 387,497
Actual, Ratio	10.46%	10.37%
For Capital Adequacy Purposes, Amount	$ 288,593	$ 224,237
For Capital Adequacy Purposes, Ratio	6.00%	6.00%
To Be Well Capitalized Under Applicable Action Provisions, Amount	$ 384,791	$ 298,982
To Be Well Capitalized Under Applicable Action Provisions, Ratio	8.00%	8.00%
Tier One Common Equity Capital	$ 503,264	$ 387,461
Tier One Common Equity Capital to Risk Weighted Assets	10.46%	10.37%
Tier One Common Equity Capital Required for Capital Adequacy	$ 216,445	$ 168,178
Tier One Common Equity Capital Required for Capital Adequacy to Risk Weighted Assets	4.50%	4.50%
Tier One Common Equity Capital Required to be Well Capitalized	$ 312,643	$ 242,923
Tier One Common Equity Capital Required to be Well Capitalized to Risk Weighted Assets	6.50%	6.50%
Tier 1 Capital (to Average Assets) [Abstract]
Actual, Amount	$ 503,312	$ 387,497
Actual, Ratio	9.68%	9.81%
For Capital Adequacy Purposes, Amount	$ 207,885	$ 157,933
For Capital Adequacy Purposes, Ratio	4.00%	4.00%
To Be Well Capitalized Under Applicable Action Provisions, Amount	$ 259,856	$ 197,417
To Be Well Capitalized Under Applicable Action Provisions, Ratio	5.00%	5.00%