Enterprise Financial Services (EFSC) 10-K 23 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 21, 2018	Jun. 30, 2017
Document and Entity Information [Abstract]
Entity Registrant Name	ENTERPRISE FINANCIAL SERVICES CORP
Entity Central Index Key	1,025,835
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		23,435,163
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 932,503,000

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets
Cash and due from banks	$ 91,084	$ 54,288
Federal funds sold	1,223	446
Interest-bearing deposits (including $1,365 and $675 pledged as collateral, respectively)	61,016	144,068
Total cash and cash equivalents	153,323	198,802
Interest-bearing deposits greater than 90 days	2,645	980
Securities available for sale	641,382	460,797
Securities held to maturity	73,749	80,463
Loans held for sale	3,155	9,562
Loans	4,097,050	3,158,161
Less: Allowance for loan losses	42,577	43,409
Total loans, net	4,054,473	3,114,752
Other real estate	498	980
Other investments, at cost	26,661	14,840
Fixed assets, net	32,618	14,910
Accrued interest receivable	14,069	11,117
State tax credits, held for sale, including $400 and $3,585 carried at fair value, respectively	43,468	38,071
Goodwill	117,345	30,334
Intangible assets, net	11,056	2,151
Other assets	114,783	103,569
Total assets	5,289,225	4,081,328
Liabilities and Shareholders' equity
Demand deposits	1,123,907	866,756
Interest-bearing transaction accounts	915,653	731,539
Money market accounts	1,342,931	1,050,472
Savings	195,150	111,435
Certificates of deposit:
Brokered	115,306	117,145
Other	463,467	356,014
Total deposits	4,156,414	3,233,361
Subordinated debentures and notes (net of debt issuance cost of $1,136 and $1,267, respectively)	118,105	105,540
Federal Home Loan Bank advances	172,743	0
Other borrowings	253,674	276,980
Accrued interest payable	1,730	1,105
Other liabilities	37,986	77,244
Total liabilities	4,740,652	3,694,230
Shareholders' equity:
Preferred stock, $0.01 par value; 5,000,000 shares authorized; 0 shares issued and outstanding	0	0
Common stock, $0.01 par value; 30,000,000 shares authorized; 23,781,112 and 20,306,353 shares issued, respectively	238	203
Treasury stock, at cost; 691,673 and 261,718 shares, respectively	(23,268)	(6,632)
Additional paid in capital	350,061	213,078
Retained earnings	225,360	182,190
Accumulated other comprehensive loss	(3,818)	(1,741)
Total shareholders' equity	548,573	387,098
Total liabilities and shareholders' equity	$ 5,289,225	$ 4,081,328

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Assets
Collateral pledged	$ 1,365	$ 675
State Tax Credits Held For Sale, Fair Value Disclosure	400	3,585
Debt issuance costs	$ 1,136	$ 1,267
Shareholders' equity:
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	30,000,000	30,000,000
Common stock, shares issued	23,781,112	20,306,353
Treasury stock, shares	691,673	261,718

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest income:
Interest and fees on loans	$ 185,452	$ 137,738	$ 122,370
Interest on debt securities:
Taxable	14,551	9,590	8,842
Nontaxable	1,283	1,300	1,215
Interest on interest-bearing deposits	804	370	211
Dividends on equity securities	449	226	141
Total interest income	202,539	149,224	132,779
Interest expense:
Interest-bearing transaction accounts	2,195	1,370	1,149
Money market accounts	8,708	4,439	2,993
Savings accounts	459	262	219
Certificates of Deposit	5,838	4,770	6,051
Subordinated debentures and notes	5,095	1,894	1,248
Federal Home Loan Bank advances	2,356	555	127
Notes payable and other borrowings	584	439	582
Total interest expense	25,235	13,729	12,369
Net interest income	177,304	135,495	120,410
Provision for portfolio loan losses	10,764	5,551	4,872
Provision reversal for purchased credit impaired loan losses	(634)	(1,946)	(4,414)
Net interest income after provision for loan losses	167,174	131,890	119,952
Noninterest income:
Service charges on deposit accounts	11,043	8,615	7,923
Wealth management revenue	8,102	6,729	7,007
Card services revenue	5,433	3,130	2,496
Gain on state tax credits, net	2,581	2,647	2,720
Gain on sale of other real estate	93	1,837	142
Gain on sale of investment securities	22	86	23
Change in FDIC loss share receivable	0	0	(5,030)
Miscellaneous income	7,120	6,015	5,394
Total noninterest income	34,394	29,059	20,675
Noninterest expense:
Employee compensation and benefits	61,388	49,846	46,095
Occupancy	9,057	6,889	6,573
Data processing	6,272	4,723	4,339
Professional fees	3,813	3,825	3,465
FDIC and other insurance	3,194	3,018	2,790
Loan legal and other real estate expense	2,220	1,635	1,812
FDIC Loss Share Termination	0	0	2,436
FDIC clawback	0	0	760
Merger Related Expenses	6,462	1,386	0
Other	22,645	14,788	13,956
Total noninterest expense	115,051	86,110	82,226
Income before income tax expense	86,517	74,839	58,401
Income tax expense	38,327	26,002	19,951
Net income	$ 48,190	$ 48,837	$ 38,450
Earnings per common share
Basic (usd per share)	$ 2.10	$ 2.44	$ 1.92
Diluted (usd per share)	$ 2.07	$ 2.41	$ 1.89

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net income	$ 48,190	$ 48,837	$ 38,450
Other comprehensive loss, net of tax:
Unrealized losses on investment securities arising during the period, net of income tax benefit of $1,265, $1,168, and $899, respectively	(2,064)	(1,906)	(1,449)
Less: Reclassification adjustment for realized gains on sale of securities available for sale included in net income, net of income tax expense of $9, $33, and $9, respectively	(13)	(53)	(14)
Total other comprehensive loss	(2,077)	(1,959)	(1,463)
Total comprehensive income	$ 46,113	$ 46,878	$ 36,987

Consolidated Statements of Com6

Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other comprehensive income, tax:
Unrealized (loss)/gain on investment securities available for sale arising during the period, tax	$ (1,265)	$ (1,168)	$ (899)
Reclassification adjustment for realized gains on sale of securities available for sale included in net income, tax	$ 9	$ 33	$ 9

Consolidated Statements of Shar

Consolidated Statements of Shareholders' Equity $ in Thousands	USD ($)	Common StockUSD ($)	Treasury StockUSD ($)	Additional paid in capitalUSD ($)	Retained earningsUSD ($)	Accumulated other comprehensive income (loss)USD ($)
Balance at Dec. 31, 2014	$ 316,241	$ 199	$ (1,743)	$ 207,731	$ 108,373	$ 1,681
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	38,450	0	0	0	38,450	0
Other comprehensive income (loss)	(1,463)	0	0	0	0	(1,463)
Cash dividends paid on common shares	(5,259)	0	0	0	(5,259)	0
Issuance under equity compensation plans, net	(1,190)	2	0	(1,192)	0	0
Share-based compensation	3,601	0	0	3,601	0	0
Excess tax benefit related to equity compensation plans	449	0	0	449	0	0
Balance at Dec. 31, 2015	$ 350,829	201	(1,743)	210,589	141,564	218
Total shares awarded to JCB shareholders	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 48,837	0	0	0	48,837	0
Other comprehensive income (loss)	(1,959)	0	0	0	0	(1,959)
Cash dividends paid on common shares	(8,211)	0	0	0	8,211	0
Repurchase of preferred stock	(4,889)	0	(4,889)	0	0	0
Issuance under equity compensation plans, net	(2,203)	2	0	(2,205)	0	0
Share-based compensation	3,367	0	0	3,367	0	0
Excess tax benefit related to equity compensation plans	1,327	0	0	1,327	0	0
Balance at Dec. 31, 2016	$ 387,098	203	(6,632)	213,078	182,190	(1,741)
Total shares awarded to JCB shareholders	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 48,190	0	0	0		0
Other comprehensive income (loss)	(2,077)	0	0	0	0	(2,077)
Cash dividends paid on common shares	(10,249)	0	0	0	(10,249)	0
Repurchase of preferred stock	(16,636)	0	(16,636)	0	0	0
Issuance under equity compensation plans, net	(2,909)	2	0	(2,911)	0	0
Shares issued in connection with acquisition of Jefferson County Bancshares, Inc., 3,299,865 shares, net	141,729	33	0	141,696	0	0
Share-based compensation	3,427	0	0	3,427	0	0
Reclassification for the adoption of ASU 2016-09	0	0	0	(5,229)	5,229	0
Balance at Dec. 31, 2017	$ 548,573	$ 238	$ (23,268)	$ 350,061	$ 225,360	$ (3,818)

Consolidated Statements of Sha8

Consolidated Statements of Shareholders' Equity (Parenthetical)	12 Months Ended
	Dec. 31, 2017$ / sharesshares	Dec. 31, 2016$ / sharesshares	Dec. 31, 2015$ / sharesshares
Cash dividends paid on common shares, per share | $ / shares	$ 0.44	$ 0.4100	$ 0.26
Issuance under equity compensation plans, shares	174,895	213,234	179,600
Stock Issued During Period, Shares, Conversion of Convertible Securities	0	0	0
Total shares awarded to JCB shareholders		0	0

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income	$ 48,190	$ 48,837	$ 38,450
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	3,281	2,428	2,022
Provision for loan losses	10,130	3,605	458
Deferred income taxes	(21,105)	(7,263)	5,763
Net amortization of debt securities	2,415	3,225	3,256
Amortization of intangible assets	2,609	924	1,089
Gain on sale of investment securities	(22)	(86)	(23)
Mortgage loans originated for sale	(138,949)	(157,129)	(135,721)
Proceeds from mortgage loans sold	145,836	154,993	133,552
Gain on sale of other real estate	(93)	(1,837)	(142)
Gain on state tax credits, net	(2,581)	(2,647)	(2,720)
Excess tax benefit of share-based compensation	0	(1,327)	(449)
Share-based compensation	3,427	3,367	3,601
Net accretion of loan discount and indemnification asset	(5,609)	(11,057)	(7,805)
Changes in:
Accrued interest receivable	(158)	(2,718)	(443)
Accrued interest payable	(27)	476	(214)
Other assets	506	(7,739)	10,457
Other liabilities	(44,269)	41,943	7,582
Net cash provided by operating activities	45,791	82,521	47,187
Cash flows from investing activities:
Net cash paid for acquisitions and dispositions	4,456	0	0
Net increase in loans	(270,090)	(328,023)	(290,326)
Net cash proceeds received from FDIC loss share receivable	0	0	2,275
Proceeds from the termination of FDIC loss share agreements	0	0	1,253
Proceeds from the sale of debt securities, available for sale	144,076	2,493	41,069
Proceeds from the paydown or maturity of debt securities, available for sale	143,949	63,502	53,733
Proceeds from the paydown or maturity of debt securities, held to maturity	6,510	3,655	2,284
Proceeds from the redemption of other investments	43,207	52,279	39,929
Proceeds from the sale of state tax credits held for sale	15,314	18,757	16,337
Proceeds from the sale of other real estate	2,779	11,346	7,378
Payments for the purchase of:
Available for sale debt securities	(325,393)	(81,195)	(152,044)
Held to maturity debt securities	0	(40,529)	0
Other investments	(56,412)	(49,645)	(36,046)
State tax credits held for sale	(18,294)	(8,201)	(20,981)
Fixed assets	(2,546)	(2,496)	(2,111)
Net cash used in investing activities	(312,444)	(358,057)	(337,250)
Cash flows from financing activities:
Net increase in noninterest-bearing deposit accounts	96,681	149,296	74,530
Net increase in interest-bearing deposit accounts	61,204	299,474	218,551
Proceeds from the issuance of subordinated notes	0	48,733	0
Proceeds from Federal Home Loan Bank advances	1,716,500	1,357,000	945,900
Repayments of Federal Home Loan Bank advances	(1,544,000)	(1,467,000)	(979,900)
Proceeds from Notes Payable	10,000	0	0
Repayments of Notes Payable	10,000	0	5,700
Debt issuance costs	(1,136)	(1,267)
Net increase (decrease) in other borrowings	(79,417)	6,654	36,143
Cash dividends paid on common stock	(10,249)	(8,211)	(5,259)
Excess tax benefit of share-based compensation	0	1,327	449
Payments for Repurchase of Common Stock	16,636	4,889	0
Payments for Repurchase of Equity	(2,909)	(2,203)	(1,190)
Net cash provided by financing activities	221,174	380,181	283,524
Net increase (decrease) in cash and cash equivalents	(45,479)	104,645	(6,539)
Cash and cash equivalents, beginning of period	198,802	94,157	100,696
Cash and cash equivalents, end of period	153,323	198,802	94,157
Supplemental disclosures of cash flow information:
Cash paid during the period for interest	24,610	13,253	12,583
Cash paid during the period for income taxes	12,449	26,039	15,763
Noncash transactions:
Real Estate Owned, Transfer to Real Estate Owned	564	2,743	8,248
Sales of other real estate financed	$ 0	$ 140	$ 0
Stock Issued During Period, Shares, Acquisitions	141,729	0	0

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES The significant accounting policies used by the Company in the preparation of the consolidated financial statements are summarized below. Business and Consolidation Enterprise Financial Services Corp and subsidiaries (the “Company” or “Enterprise”) is a financial holding company that provides a full range of banking and wealth management services to individuals and corporate customers primarily located in the St. Louis, Kansas City, and Phoenix metropolitan markets through its banking subsidiary, Enterprise Bank & Trust (the “Bank”). The consolidated financial statements include the accounts of the Company, and its subsidiaries, all of which are wholly owned. All intercompany accounts and transactions have been eliminated. The Company is subject to competition from other financial and nonfinancial institutions providing financial services in the markets served by the Company's subsidiary. Additionally, the Company and its banking subsidiary are subject to the regulations of certain federal and state agencies and undergo periodic examinations by those regulatory agencies. The Company has one operating segment. Use of Estimates The consolidated financial statements of the Company have been prepared in conformity with U.S. generally accepted accounting principles (“U.S. GAAP”). In preparing the consolidated financial statements, management is required to make estimates and assumptions, which significantly affect the reported amounts in the consolidated financial statements. Such estimates include the valuation of loans, goodwill, intangible assets, indemnification assets, and other long-lived assets, along with assumptions used in the calculation of income taxes, among others. These estimates and assumptions are based on management's best estimates and judgment. Management evaluates its estimates and assumptions on an ongoing basis using experience and other factors, including the current economic environment, which management believes to be reasonable under the circumstances. Management adjusts such estimates and assumptions when facts and circumstances dictate. Decreased real estate values, volatile credit markets, and unemployment have combined to increase the uncertainty inherent in such estimates and assumptions. As future events and their effects cannot be determined with precision, actual results could differ significantly from these estimates. Changes in those estimates resulting from continuing changes in the economic environment will be reflected in the financial statements in future periods. Cash Flow Information For purposes of reporting cash flows, the Company considers cash and due from banks, interest-bearing deposits and federal funds sold that mature within 90 days of the balance sheet date to be cash and cash equivalents. At December 31, 2017 and 2016 , approximately $17.5 million , and $18.2 million , respectively, of cash and due from banks represented required reserves on deposits maintained by the Company in accordance with Federal Reserve Bank requirements. Investments The Company has classified all investments in debt securities as available for sale or held to maturity. Securities classified as available for sale are carried at fair value. Unrealized holding gains and losses for available for sale securities are excluded from earnings and reported as a net amount in a separate component of shareholders' equity until realized. All previous fair value adjustments included in the separate component of shareholders' equity are reversed upon sale. Securities classified as held to maturity are carried at historical cost and adjusted for amortization of premiums and accretion of discounts. Declines in the fair value of securities below their cost deemed to be other-than-temporary are reflected in operations as realized losses. In estimating other-than-temporary impairment losses, management systematically evaluates investment securities for other-than-temporary declines in fair value on a quarterly basis. This analysis requires management to consider various factors, which include (1) the present value of the cash flows expected to be collected compared to the amortized cost of the security, (2) duration and magnitude of the decline in value, (3) the financial condition of the issuer or issuers, (4) structure of the security, and (5) the intent to sell the security or whether it's more likely than not the Company would be required to sell the security before its anticipated recovery in market value. Premiums and discounts are amortized or accreted over the expected lives of the respective securities as an adjustment to yield using the interest method. Dividend and interest income is recognized when earned. Realized gains and losses are included in earnings and are derived using the specific identification method for determining the cost of securities sold. Loans Held for Sale The Company provides long-term financing of one-to-four-family residential real estate by originating fixed and variable rate loans. Long-term fixed and variable rate loans are sold into the secondary market with limited recourse. Upon receipt of an application for a real estate loan, the Company determines whether the loan will be sold into the secondary market or retained in the Company's loan portfolio. The interest rates on the loans sold are locked with the buyer and the Company bears no interest rate risk related to these loans. Mortgage loans held for sale are carried at the lower of cost or fair value, which is determined on a specific identification method. The Company does not retain servicing on any loans sold, nor did the Company have any capitalized mortgage servicing rights at December 31, 2017 or 2016 . Gains on the sale of loans held for sale are reported net of direct origination fees and costs in the Company's consolidated statements of operations. Portfolio Loans Loans are reported at the principal balance outstanding, net of unearned fees, costs, and premiums or discounts on acquired loans. Loan origination fees, direct origination costs, and premiums or discounts resulting from acquired loans are deferred and recognized over the lives of the related loans as a yield adjustment using the interest method. Interest income on loans is accrued to income based on the principal amount outstanding. The recognition of interest income is discontinued when a loan becomes 90 days past due or a significant deterioration in the borrower's credit has occurred which, in management's judgment, negatively impacts the collectibility of the loan. Unpaid interest on such loans is reversed at the time the loan becomes uncollectible and subsequent interest payments received are applied to principal if any doubt exists as to the collectibility of such principal; otherwise, such receipts are recorded as interest income. Loans that have not been restructured are returned to accrual status when management believes full collectibility of principal and interest is expected. Non-accrual loans that have been restructured will remain in a non-accrual status until the borrower has made at least six months of consecutive contractual payments. Purchased Credit Impaired ("PCI") Loans PCI loans were acquired in a business combination or transaction, that have evidence of deterioration of credit quality since origination and for which it is probable, at acquisition, that the Company will be unable to collect all contractually required payments receivable. PCI loans were initially recorded at fair value (as determined by the present value of expected future cash flows) with no valuation allowance. The difference between the undiscounted cash flows expected at acquisition and the investment in the loans, or the “accretable yield,” is recognized as interest income on a level-yield method over the life of the loans. Contractually required payments for interest and principal that exceed the undiscounted cash flows expected at acquisition, or the “nonaccretable difference,” are not recognized as a yield adjustment or as a loss accrual or a valuation allowance. The Company aggregates individual loans with common risk characteristics into pools of loans. Increases in expected cash flows subsequent to the initial investment are recognized prospectively through adjustment of the yield on the loans over their remaining lives. Decreases in expected cash flows due to an inability to collect contractual cash flows are recognized as impairment through the provision for loan losses account. Any allowance for loan loss on these pools reflect only losses incurred after the acquisition. Disposals of loans, including sales of loans, paydowns, payments in full or foreclosures result in the removal or reduction of the loan from the loan pool. PCI loans are generally considered accruing and performing, as the loans accrete income over the estimated life of the loan, in circumstances where cash flows are reasonably estimable by management. Accordingly, PCI loans that could be contractually past due could be considered to be accruing and performing. If the timing and amount of future cash flows is not reasonably estimable or is less than the carrying value, the loans may be classified as nonaccrual loans and the purchase price discount on those loans is not recorded as interest income until the timing and amount of future cash flows can be reasonably estimable. Impaired Loans Loans are considered “impaired” when it becomes probable that the Company will be unable to collect all amounts due according to the loan's contractual terms. Non-accrual loans, loans past due greater than 90 days and still accruing, unless adequately secured and in the process of collection, and restructured loans qualify as “impaired loans.” Restructured loans involve the granting of a concession to a borrower experiencing financial difficulty involving the modification of terms of the loan, such as changes in payment schedule or interest rate. When measuring impairment, the expected future cash flows of an impaired loan are discounted at the loan's effective interest rate at origination. Alternatively, impairment can be measured by reference to an observable market price, if one exists, or the fair value of the collateral for a collateral-dependent loan. Interest income on impaired loans is not accrued but is recorded when cash is received and only if principal is considered to be fully collectible. Loans and leases, which are deemed uncollectible, are charged off to the allowance for loan losses, while recoveries of amounts previously charged off are credited to the allowance for loan losses. Impaired loans exclude PCI loans, as described above. Although, if the timing and amount of future cash flows is not reasonably estimable, the loans may be classified as nonaccrual loans and the purchase price discount on those loans is not recorded as interest income until the timing and amount of future cash flows can be reasonably estimated. See Note 5 – Loans for more information on these loans. Loans are generally placed on non-accrual status when contractually past due 90 days or more as to interest or principal payments. Additionally, whenever management becomes aware of facts or circumstances that may adversely impact the collectability of principal or interest on loans, it is management's practice to place such loans on non-accrual status immediately, rather than delaying such action until the loans become 90 days past due. Previously accrued and uncollected interest on such loans is reversed. Income is recorded only to the extent that a determination has been made that the principal balance of the loan is collectable and the interest payments are subsequently received in cash, or for a restructured loan, the borrower has made six consecutive contractual payments. If collectability of the principal is in doubt, payments received are applied to loan principal. Loans past due 90 days or more but still accruing interest are also generally included in nonperforming loans. Loans past due 90 days or more but still accruing are classified as such where the underlying loans are both well secured (the collateral value is sufficient to cover principal and accrued interest) and are in the process of collection. At December 31, 2017 , we did not have any loans past due greater than 90 days and not included in nonperforming loans. Loan Charge-Offs Loans are charged-off when the primary and secondary sources of repayment (cash flow, collateral, guarantors, etc.) are less than their carrying value. Allowance For Loan Losses The allowance for loan losses is increased by provision charged to expense and is available to absorb charge-offs, net of recoveries. Management utilizes a systematic, documented approach in determining the appropriate level of the allowance for loan losses. The level of the allowance reflects management's continuing evaluation of industry concentrations; specific credit risks; loan loss experience; current loan portfolio quality; present economic, political and regulatory conditions; and probable losses inherent in the current loan portfolio. The determination of the appropriate level of the allowance for loan losses inherently involves a degree of subjectivity and requires that the Company make significant estimates of current credit risks and future trends, all of which may undergo material changes. Changes in economic conditions affecting borrowers, new information regarding existing loans, identification of additional problem loans and other factors, both within and outside of our control, may require an increase in the allowance for loan losses. Management believes the allowance for loan losses is adequate to absorb inherent losses in the loan portfolio. While management uses available information to recognize losses on loans, future additions to the allowance may be necessary based on changes in economic conditions and other factors. In addition, various regulatory agencies, as an integral part of the examination process, periodically review the Bank's loan portfolio. Such agencies may require additions to the allowance for loan losses based on their judgments and interpretations of information available to them at the time of their examinations. Allowance for Loan Losses on PCI Loans The Company updates its cash flow projections for PCI loans on a periodic basis. Assumptions utilized in this process include projections related to probability of default, loss severity, prepayment, extensions and recovery lag. Projections related to probability of default and prepayment are calculated utilizing a loan migration analysis and management's assessment of loss exposure including the fair value of underlying collateral. The loan migration analysis is a matrix that specifies the probability of a loan pool transitioning into a particular delinquency or liquidation state given its current performance at the measurement date. Loss severity factors are based upon industry data and historical experience. Any decreases in expected cash flows after the acquisition date and subsequent measurement periods are recognized by recording an impairment in allowance for loan losses. Other Real Estate Other real estate represents property acquired through foreclosure or deeded to the Company in lieu of foreclosure on loans on which the borrowers have defaulted on the payment of principal or interest. Other real estate is recorded on an individual asset basis at the lower of cost or fair value less estimated costs to sell. The fair value of other real estate is based upon estimates of future cash flows, market value of similar assets, if available, or independent appraisals. These estimates involve significant uncertainties and judgments. As a result, fair value estimates may not be realizable in a current sale or settlement of the other real estate. Subsequent reductions in fair value are expensed within noninterest expense. Gains and losses resulting from the sale of other real estate are credited or charged to current period earnings. Costs of maintaining and operating other real estate are expensed as incurred, and expenditures to complete or improve other real estate properties are capitalized if the expenditures are expected to be recovered upon ultimate sale of the property. Fixed Assets Buildings, leasehold improvements, furniture, fixtures, equipment, and capitalized software are stated at cost less accumulated depreciation. All categories are computed using the straight-line method over their respective estimated useful lives. Furniture, fixtures and equipment is depreciated over three to ten years, buildings and leasehold improvements over ten to forty years, and capitalized software over three years based upon estimated lives or lease obligation periods. State Tax Credits Held for Sale The Company has purchased the rights to receive 10 -year streams of state tax credits at agreed upon discount rates and sells such tax credits to its clients and others. All state tax credits purchased prior to 2009 are accounted for at fair value. All state tax credits purchased since 2009 are accounted for at cost. The Company elected not to account for the state tax credits purchased since 2009 at fair value in order to limit the volatility of the fair value changes in the Company's consolidated statements of operations. Cash Surrender Value of Life Insurance The Company has purchased bank-owned life insurance policies on certain bank officers. Bank-owned life insurance is recorded at its cash surrender value. Changes in the cash surrender values are included in noninterest income. Federal Home Loan Bank Stock The Bank, as a member of the Federal Home Loan Bank of Des Moines (“FHLB”), is required to maintain an investment in the capital stock of the FHLB. The stock is redeemable at par by the FHLB, and is, therefore, carried at cost and periodically evaluated for impairment. The Company records FHLB dividends in interest income. Goodwill and Other Intangible Assets The Company tests goodwill for impairment on an annual basis and whenever events or changes in circumstances indicate that the Company may not be able to recover the respective asset's carrying amount. The Company's annual test for impairment was performed in the fourth quarter of December 31, 2017 . Such tests involve the use of estimates and assumptions. Core deposit intangibles are amortized using an accelerated method over an estimated useful life of approximately 10 years. Potential impairments to goodwill must first be identified by performing a qualitative assessment which evaluates relevant events or circumstances to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount. If this test indicates it is more likely than not that goodwill has been impaired, then a quantitative impairment test is completed. The quantitative impairment test calculates the fair value of the reporting unit and compares it with its carrying amount, including goodwill. If the carrying amount of goodwill exceeds its implied fair market value, an impairment loss is recognized. That loss is equal to the carrying amount of goodwill that is in excess of its implied fair market value. Impairment of Long-Lived Assets Long-lived assets, such as fixed assets and purchased intangibles subject to amortization, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to estimated undiscounted future cash flows expected to be generated by the asset. If the carrying amount of an asset exceeds its estimated future cash flows, an impairment charge is recognized in the amount by which the carrying amount of the asset exceeds the fair value of the asset. Assets to be disposed of are separately presented in the balance sheet and reported at the lower of the carrying amount or fair value less costs to sell, and are no longer depreciated. The assets and liabilities of a disposal group classified as held for sale are presented separately in the appropriate asset and liability sections of the balance sheet. Derivative Financial Instruments and Hedging Activities The Company uses derivative financial instruments to assist in the management of interest rate sensitivity and to modify the repricing, maturity and option characteristics of certain assets and liabilities. In addition, the Company also offers an interest rate hedge program that includes interest rate swaps to assist its customers in managing their interest rate risk profile. In order to eliminate the interest rate risk associated with offering these products, the Company enters into derivative contracts with third parties to offset the customer contracts. Derivative instruments are required to be measured at fair value and recognized as either assets or liabilities in the consolidated financial statements. Fair value represents the payment the Company would receive or pay if the item were sold or bought in a current transaction. The accounting for changes in fair value (gains or losses) of a hedged item is dependent on whether the related derivative is designated and qualifies for “hedge accounting.” The Company assigns derivatives to one of these categories at the purchase date: cash flow hedge, fair value hedge, or non-designated derivatives. An assessment of the expected and ongoing hedge effectiveness of any derivative designated a fair value hedge or cash flow hedge is performed as required by the accounting standards. Derivatives are included in other assets and other liabilities in the consolidated balance sheets. Generally, the only derivative instruments used by the Company have been interest rate swaps and interest rate caps. The Company does not currently have derivative instruments designated as fair value or cash flow hedges. Certain derivative financial instruments are not designated as cash flow or as fair value hedges for accounting purposes. These non-designated derivatives are intended to provide interest rate protection on net interest income or noninterest income but do not meet hedge accounting treatment. Customer accommodation interest rate swap contracts are not designated as hedging instruments. Changes in the fair value of these instruments are recorded in interest income or noninterest income in the consolidated statements of income depending on the underlying hedged item. Income Taxes The Company and its subsidiaries file a consolidated federal income tax return. Deferred tax assets and liabilities are recognized for the estimated future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates in effect for the year in which those temporary differences are expected to be recovered or settled. We evaluated the need for deferred tax asset valuation allowances based on a more-likely-than-not standard. The ability to realize deferred tax assets depends on the ability to generate sufficient positive taxable income within the carryback or carryforward periods provided for in the laws for each applicable taxing jurisdiction. We consider the following possible sources of taxable income: future reversal patterns of existing taxable temporary differences, future taxable income exclusive of reversing temporary differences, taxable income in prior carryback years and the availability of qualified tax planning strategies. The assessment regarding whether a valuation allowance is required or should be adjusted depends on all available positive and negative factors including, but not limited to, nature, frequency, and severity of recent losses, duration of available carryforward periods, experience with tax attributes expiring unused and near and medium term financial outlook. Because of the complexity of tax laws and regulations, interpretation can be difficult and subject to legal judgment given specific facts and circumstances. It is possible that others, given the same information, may at any point in time reach different reasonable conclusions regarding the estimated amounts of accrued taxes. The SEC staff issued SAB 118, which provides guidance on accounting for the tax effects of the Tax Cuts and Jobs Act of 2017 (“Tax Act”). SAB 118 provides a measurement period that should not extend beyond one year from the Tax Act enactment date for companies to complete the accounting under ASC 740. In accordance with SAB 118, a company must reflect the income tax effects of those aspects of the Act for which the accounting under ASC 740 is complete. To the extent that a company’s accounting for certain income tax effects of the Tax Act is incomplete but it is able to determine a reasonable estimate, it must record a provisional estimate in the financial statements. If a company cannot determine a provisional estimate to be included in the financial statements, it should continue to apply ASC 740 on the basis of the provisions of the tax laws that were in effect immediately before the enactment of the Tax Act. The Company has recorded amounts based on the information known and reasonable estimates used as of December 31, 2017, but are subject to change based on a number of factors. The Company will complete its analysis of certain tax positions at the time it files its tax returns for the year ended December 31, 2017 and will be able to conclude if any further adjustments to the provisional estimate of the impact recorded is required. Stock-Based Compensation Stock-based compensation is recognized as an expense for stock options, restricted stock awards, and restricted stock units granted to employees in return for employee service. Equity classified awards are measured at the grant date fair value using either an observable market value or a valuation methodology, and recognized over the requisite service period on a straight-line basis. Forfeitures are recorded as they occur. A description of the Company's stock-based employee compensation plan is described in Note 15 - Compensation Plans. Acquisitions and Divestitures Acquisitions and business combinations are accounted for using the acquisition method of accounting. The assets and liabilities of the acquired entities have been recorded at their estimated fair values at the date of acquisition. Goodwill represents the excess of the purchase price over the fair value of net assets acquired, including the amount assigned to identifiable intangible assets. The purchase price allocation process requires an estimation of the fair values of the assets acquired and the liabilities assumed. When a business combination agreement provides for an adjustment to the cost of the combination contingent on future events, the Company includes an estimate of the acquisition-date fair value as part of the cost of the combination. To determine the fair values, the Company relies on third party valuations, such as appraisals, or internal valuations based on discounted cash flow analyses or other valuation techniques. The results of operations of the acquired business are included in the Company's consolidated financial statements from the date of acquisition. Merger-related costs are costs the Company incurs to effect a business combination. In 2017, the Company changed its presentation of Merger related expenses as a separate component of Noninterest expenses on the Condensed Consolidated Statements of Operations. Merger related expenses include costs directly related to merger or acquisition activity and include legal and professional fees, system consolidation and conversion costs, and compensation costs such as severance and retention incentives for employees impacted by acquisition activity. The Company accounts for merger-related costs as expenses in the periods in which the costs are incurred and the services are received. For divestitures, the Company measures an asset (disposal group) classified as held for sale at the lower of its carrying value at the date the asset is initially classified as held for sale or its fair value less costs to sell. The Company reports the results of operations of an entity or group of components that either has been disposed of or held for sale as discontinued operations only if the disposal of that component represents a strategic shift that has or will have a major effect on an entity's operations and financial results. Any incremental direct costs incurred to transact the sale are allocated against the gain or loss on the sale. These costs would include items like legal fees, title transfer fees, broker fees, etc. Any goodwill and intangible assets associated with the portion of the reporting unit to be disposed of is included in the carrying amount of the business in determining the gain or loss on the sale. Basic and Diluted Earnings Per Common Share Basic earnings per common share data is calculated by dividing net income available to common shareholders by the weighted average number of common shares outstanding during the period. Common shares outstanding include common stock and restricted stock awards where recipients have satisfied the vesting terms. Diluted earnings per common share gives effect to all dilutive potential common shares outstanding during the period using the treasury stock method. Consolidated Statement of Comprehensive Income The Consolidated Statement of Comprehensive Income includes the amount and the related tax impact that have been reclassified from accumulated other comprehensive income to net income. The classification adjustment for unrealized loss/gain on sale of securities included in net income has been recorded through the gain on sale of investment securities line item, within noninterest income, in the Company's Consolidated Statements of Operations. Reclassifications Some items in the prior year financial statements were reclassified to conform to the current presentation. In 2017, the Company changed its presentation of loans on the face of the Consolidated Balance Sheets to combine originated loans with purchased loans. See Note 5 - Loans for more information. The Company also changed its presentation of the Noninterest Income section on the face of the Consolidated Statements of Operations to separate card services revenue from other service charges and fee income. The difference was reclassified into miscellaneous income. Merger related expenses were reclassified from other expenses to be a separate component of the Noninterest Expense section on the Consolidated Statements of Operations. Reclassifications had no effect on prior year net income or shareholders' equity.

Acquisitions & Divestitures

Acquisitions & Divestitures	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Mergers, Acquisitions and Dispositions Disclosures [Text Block]	ACQUISITIONS & DIVESTITURES Acquisition of Jefferson County Bancshares, Inc. On February 10, 2017, the Company closed its acquisition of 100% of Jefferson County Bancshares, Inc. ("JCB") and its wholly-owned subsidiary, Eagle Bank and Trust Company of Missouri. JCB operated 13 full service retail and commercial banking offices in the metropolitan St. Louis area and one in Perry County, Missouri. JCB shareholders received, based on their election, cash consideration in an amount of $85.39 per share of JCB common stock or 2.75 shares of EFSC common stock per share of JCB common stock, subject to allocation and proration procedures. Aggregate consideration at closing was 3.3 million shares of EFSC common stock and $29.3 million cash paid to JCB shareholders and holders of JCB stock options. Based on EFSC’s closing stock price of $42.95 on February 10, 2017, the overall transaction had a value of $171.0 million , including JCB’s common stock and stock options. The Company also recognized $6.5 million and $1.4 million of merger related costs that were recorded in noninterest expense in the statement of operations for the years ended December 31, 2017 and 2016, respectively. The acquisition of JCB has been accounted for as a business combination using the acquisition method of accounting which requires assets acquired and liabilities assumed to be recognized at fair value as of the acquisition date. Goodwill of $87.0 million arising from the acquisition consists largely of the synergies and economies of scale expected from combining the operations of JCB into Enterprise. The goodwill is assigned as part of the Company's Banking reporting unit. None of the goodwill recognized is expected to be deductible for income tax purposes. The following table presents the assets acquired and liabilities assumed of JCB as of February 10, 2017, and their estimated fair values: (in thousands) As Recorded by JCB Adjustments As Recorded by EFSC Assets acquired: Cash and cash equivalents $ 33,739 $ — $ 33,739 Interest-bearing deposits 1,715 — 1,715 Securities 148,670 — 148,670 Portfolio loans, net 685,905 (11,094 ) (a) 674,811 Other real estate owned 6,762 (5,082 ) (b) 1,680 Other investments 2,695 — 2,695 Fixed assets, net 21,780 (3,325 ) (c) 18,455 Accrued interest receivable 2,794 — 2,794 Goodwill 7,806 (7,806 ) (d) — Other intangible assets 25 11,489 (e) 11,514 Deferred tax assets 4,634 3,991 (f) 8,625 Other assets 19,107 (296 ) (g) 18,811 Total assets acquired $ 935,632 $ (12,123 ) $ 923,509 Liabilities assumed: Deposits $ 764,539 $ 629 (h) $ 765,168 Other borrowings 55,430 681 (i) 56,111 Trust preferred securities 12,887 (382 ) (j) 12,505 Accrued interest payable 653 — 653 Other liabilities 5,006 65 5,071 Total liabilities assumed $ 838,515 $ 993 $ 839,508 Net assets acquired $ 97,117 $ (13,116 ) $ 84,001 Consideration paid: Cash $ 29,283 Common stock 141,729 Total consideration paid $ 171,012 Goodwill $ 87,011 (a) Fair value adjustments based on the Company’s evaluation of the acquired loan portfolio, write-off of net deferred loan costs, reclassification from other real estate owned, and elimination of the allowance for loan losses recorded by JCB. The fair value discount recorded to the loan portfolio is $24.7 million , inclusive of the allowance for loan losses previously recorded by JCB. (b) Fair value adjustment based on the Company’s evaluation of the acquired other real estate portfolio, and reclassification to portfolio loans. (c) Fair value adjustments based on the Company’s evaluation of the acquired premises and equipment. (d) Eliminate JCB’s recorded goodwill. (e) Record the core deposit intangible asset on the acquired core deposit accounts. Amount to be amortized using a sum of years digits method over a 10 year useful life. (f) Adjustment for deferred taxes at the acquisition date. (g) Fair value adjustment based on evaluation of other assets. (h) Fair value adjustment to time deposits based on current interest rates. (i) Fair value adjustment to the FHLB advances based on current interest rates. (j) Fair value adjustment based on the Company's evaluation of the trust preferred securities. The following table provides the unaudited pro forma information for the results of operations for the twelve months ended December 31, 2017 and 2016, as if the acquisition had occurred on January 1, 2016. The pro forma results combine the historical results of JCB with the Company’s Consolidated Statements of Income, adjusted for the impact of the application of the acquisition method of accounting including loan discount accretion, intangible assets amortization, and deposit and trust preferred securities premium accretion, net of taxes. The pro forma results have been prepared for comparative purposes only and are not necessarily indicative of the results that would have been obtained had the acquisition actually occurred on January 1, 2016. No assumptions have been applied to the pro forma results of operations regarding possible revenue enhancements, expense efficiencies or asset dispositions. Only the acquisition related expenses that have been incurred as of December 31, 2017 are included in net income in the table below. Pro Forma Twelve months ended December 31, (in thousands, except per share data) 2017 2016 Total revenues (net interest income plus noninterest income) $ 213,910 $ 199,033 Net income 47,227 56,994 Diluted earnings per common share 2.03 2.42

Earnings Per Share

Earnings Per Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings Per Share	EARNINGS PER SHARE The following table presents a summary of per common share data and amounts for the periods indicated. Years ended December 31, (in thousands, except per share data) 2017 2016 2015 Net income as reported $ 48,190 $ 48,837 $ 38,450 Weighted average common shares outstanding 22,953 20,003 19,984 Additional dilutive common stock equivalents 296 287 333 Weighted average diluted common shares outstanding 23,249 20,290 20,317 Basic earnings per common share: $ 2.10 $ 2.44 $ 1.92 Diluted earnings per common share: $ 2.07 $ 2.41 $ 1.89 There were no common stock equivalents for fiscal years 2017, and 2016, and 0.1 million common stock equivalents for fiscal year 2015 , which were excluded from the earnings per share calculation because their effect was anti-dilutive.

Investments

Investments	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Investments	INVESTMENTS The following table presents the amortized cost, gross unrealized gains and losses and fair value of securities available for sale and held to maturity: December 31, 2017 (in thousands) Amortized Cost Gross Gross Fair Value Available for sale securities: Obligations of U.S. Government-sponsored enterprises $ 99,878 $ 6 $ (660 ) $ 99,224 Obligations of states and political subdivisions 34,181 674 (213 ) 34,642 Agency mortgage-backed securities 513,082 727 (6,293 ) 507,516 Total securities available for sale $ 647,141 $ 1,407 $ (7,166 ) $ 641,382 Held to maturity securities: Obligations of states and political subdivisions $ 14,031 $ 69 $ (46 ) $ 14,054 Agency mortgage-backed securities 59,718 16 (330 ) 59,404 Total securities held to maturity $ 73,749 $ 85 $ (376 ) $ 73,458 December 31, 2016 (in thousands) Amortized Cost Gross Gross Fair Value Available for sale securities: Obligations of U.S. Government-sponsored enterprises $ 107,312 $ 348 $ — $ 107,660 Obligations of states and political subdivisions 36,486 630 (485 ) 36,631 Agency mortgage-backed securities 319,345 1,101 (3,940 ) 316,506 Total securities available for sale $ 463,143 $ 2,079 $ (4,425 ) $ 460,797 Held to maturity securities: Obligations of states and political subdivisions $ 14,759 $ 11 $ (242 ) $ 14,528 Agency mortgage-backed securities 65,704 45 (638 ) 65,111 Total securities held to maturity $ 80,463 $ 56 $ (880 ) $ 79,639 At December 31, 2017 , and 2016 , there were no holdings of securities of any one issuer in an amount greater than 10% of shareholders’ equity, other than the U.S. Government agencies and sponsored enterprises. The agency mortgage-backed securities are all issued by U.S. Government-sponsored enterprises. Securities having a fair value of $500.0 million and $407.3 million at December 31, 2017 , and December 31, 2016 , respectively, were pledged as collateral to secure deposits of public institutions and for other purposes as required by law or contract provisions. The amortized cost and estimated fair value of debt securities at December 31, 2017 , by contractual maturity, are shown below. Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. The weighted average life of the agency mortgage-backed securities is approximately 4 years. Available for sale Held to maturity (in thousands) Amortized Cost Estimated Fair Value Amortized Cost Estimated Due in one year or less $ 3,060 $ 3,076 $ — $ — Due after one year through five years 110,910 110,480 186 195 Due after five years through ten years 14,573 14,980 12,977 12,981 Due after ten years 5,516 5,330 868 878 Agency mortgage-backed securities 513,082 507,516 59,718 59,404 $ 647,141 $ 641,382 $ 73,749 $ 73,458 The following table represents a summary of investment securities that had an unrealized loss: December 31, 2017 Less than 12 months 12 months or more Total (in thousands) Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Obligations of U.S. Government-sponsored enterprises $ 89,309 $ 660 $ — $ — $ 89,309 $ 660 Obligations of states and political subdivisions 13,951 259 — — 13,951 259 Agency mortgage-backed securities 469,655 6,034 12,229 589 481,884 6,623 $ 572,915 $ 6,953 $ 12,229 $ 589 $ 585,144 $ 7,542 December 31, 2016 Less than 12 months 12 months or more Total (in thousands) Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Obligations of states and political subdivisions $ 21,361 $ 408 $ 3,553 $ 320 $ 24,914 $ 728 Agency mortgage-backed securities 267,734 4,084 12,883 493 280,617 4,577 $ 289,095 $ 4,492 $ 16,436 $ 813 $ 305,531 $ 5,305 The unrealized losses at both December 31, 2017 , and 2016 , were primarily attributable to changes in market interest rates since the securities were purchased. Management systematically evaluates investment securities for other-than-temporary declines in fair value on a quarterly basis. This analysis requires management to consider various factors, which include among other considerations (1) the present value of the cash flows expected to be collected compared to the amortized cost of the security, (2) duration and magnitude of the decline in value, (3) the financial condition of the issuer or issuers, (4) structure of the security, and (5) the intent to sell the security or whether it is more likely than not that the Company would be required to sell the security before its anticipated recovery in market value. At December 31, 2017 and 2016 , management performed its quarterly analysis of all securities with an unrealized loss and concluded no individual securities were other-than-temporarily impaired. The gross gains and losses realized from sales of available for sale investment securities were as follows: December 31, (in thousands) 2017 2016 2015 Gross gains realized $ 22 $ 86 $ 63 Gross losses realized — — (40 ) Proceeds from sales 144,076 2,493 41,069 Other Investments, At Cost At December 31, 2017 , and 2016 , other investments, at cost, totaled $26.7 million , and $14.8 million , respectively. As a member of the FHLB system administered by the Federal Housing Finance Agency, the Bank is required to maintain a minimum investment in capital stock with the FHLB Des Moines consisting of membership stock and activity-based stock. The FHLB capital stock of $12.9 million , and $4.4 million at December 31, 2017 , and 2016 , respectively, is recorded at cost, which represents redemption value, and is included in other investments in the consolidated balance sheets. The remaining amounts in other investments include various investments in SBICs and the Company's investment in unconsolidated trusts used to issue preferred securities to third parties (see Note 10 – Subordinated Debentures).

Portfolio Loans

Portfolio Loans	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Portfolio Loans	LOANS The loan portfolio is comprised of loans originated by the Company and loans that were acquired in connection with the Company’s acquisitions. These loans are accounted for using the guidance in the Accounting Standards Codification (ASC) section 310-30 and 310-20. Loans accounted for using ASC 310-30 are sometimes referred to as purchased credit impaired, or PCI, loans. The table below shows the loan portfolio composition including carrying value by segment of loans accounted for at amortized cost, which includes our originated loans, and loans accounted for as PCI. (in thousands) December 31, 2017 December 31, 2016 Loans accounted for at amortized cost $ 4,022,896 $ 3,118,392 Loans accounted for as PCI 74,154 39,769 Total loans $ 4,097,050 $ 3,158,161 The following tables refer to loans not accounted for as PCI loans. Below is a summary of loans by category at December 31, 2017 and 2016 : (in thousands) December 31, 2017 December 31, 2016 Commercial and industrial $ 1,918,720 $ 1,632,714 Real estate loans: Commercial - investor owned 769,275 544,808 Commercial - owner occupied 554,589 350,148 Construction and land development 303,091 194,542 Residential 341,312 240,760 Total real estate loans 1,968,267 1,330,258 Consumer and other 137,234 156,182 Loans, before unearned loan (fees) costs 4,024,221 3,119,154 Unearned loan (fees) costs, net (1,325 ) (762 ) Loans, including unearned loan fees $ 4,022,896 $ 3,118,392 Following is a summary of activity for the years ended December 31, 2017 , 2016 , and 2015 of loans to executive officers and directors, or to entities in which such individuals had beneficial interests as a shareholder, officer, or director. Such loans were made in the normal course of business on substantially the same terms, including interest rates and collateral, as those prevailing at the time for comparable transactions with other customers and did not involve more than the normal risk of collectibility. (in thousands) December 31, 2017 December 31, 2016 December 31, 2015 Balance at beginning of year $ 15,406 $ 4,394 $ 13,513 New loans and advances 1,353 11,539 641 Payments and other reductions (11,410 ) (527 ) (9,760 ) Balance at end of year $ 5,349 $ 15,406 $ 4,394 A summary of activity in the allowance for loan losses and the recorded investment in loans by class and category based on impairment method for the years ended indicated below is as follows: (in thousands) Commercial and industrial CRE - investor owned CRE - owner occupied Construction and land development Residential real estate Consumer and other Total Balance at December 31, 2017 Allowance for loan losses: Balance, beginning of year $ 26,996 $ 3,420 $ 2,890 $ 1,304 $ 2,023 $ 932 $ 37,565 Provision (provision reversal) 8,737 456 404 336 797 34 10,764 Losses charged off (9,872 ) (117 ) (90 ) (254 ) (973 ) (201 ) (11,507 ) Recoveries 545 131 104 101 390 73 1,344 Balance, end of year $ 26,406 $ 3,890 $ 3,308 $ 1,487 $ 2,237 $ 838 $ 38,166 Balance at December 31, 2016 Allowance for loan losses: Balance, beginning of year $ 22,056 $ 3,484 $ 2,969 $ 1,704 $ 1,796 $ 1,432 $ 33,441 Provision (provision reversal) 6,569 (11 ) (1,202 ) (1,334 ) 129 1,400 5,551 Losses charged off (2,303 ) (95 ) — — (25 ) (1,912 ) (4,335 ) Recoveries 674 42 1,123 934 123 12 2,908 Balance, end of year $ 26,996 $ 3,420 $ 2,890 $ 1,304 $ 2,023 $ 932 $ 37,565 Balance at December 31, 2015 Allowance for loan losses: Balance, beginning of year $ 16,983 $ 4,382 $ 3,135 $ 1,715 $ 2,830 $ 1,140 $ 30,185 Provision (provision reversal) 6,976 (303 ) (1,626 ) (335 ) (58 ) 218 4,872 Losses charged off (3,699 ) (664 ) (38 ) (350 ) (1,313 ) (27 ) (6,091 ) Recoveries 1,796 69 1,498 674 337 101 4,475 Balance, end of year $ 22,056 $ 3,484 $ 2,969 $ 1,704 $ 1,796 $ 1,432 $ 33,441 (in thousands) Commercial and industrial CRE - investor owned CRE - owner occupied Construction and land development Residential real estate Consumer and other Total Balance December 31, 2017 Allowance for loan losses - Ending balance: Individually evaluated for impairment $ 2,508 $ — $ 71 $ — $ — $ — $ 2,579 Collectively evaluated for impairment 23,898 3,890 3,237 1,487 2,237 838 35,587 Total $ 26,406 $ 3,890 $ 3,308 $ 1,487 $ 2,237 $ 838 $ 38,166 Loans - Ending balance: Individually evaluated for impairment $ 12,665 $ 422 $ 1,975 $ 136 $ 1,602 $ 375 $ 17,175 Collectively evaluated for impairment 1,906,055 768,853 552,614 302,955 339,710 135,534 4,005,721 Total $ 1,918,720 $ 769,275 $ 554,589 $ 303,091 $ 341,312 $ 135,909 $ 4,022,896 Balance December 31, 2016 Allowance for loan losses - Ending balance: Individually evaluated for impairment $ 2,909 $ — $ — $ 155 $ — $ — $ 3,064 Collectively evaluated for impairment 24,087 3,420 2,890 1,149 2,023 932 34,501 Total $ 26,996 $ 3,420 $ 2,890 $ 1,304 $ 2,023 $ 932 $ 37,565 Loans - Ending balance: Individually evaluated for impairment $ 12,523 $ 430 $ 1,854 $ 1,903 $ 62 $ — $ 16,772 Collectively evaluated for impairment 1,620,191 544,378 348,294 192,639 240,698 155,420 3,101,620 Total $ 1,632,714 $ 544,808 $ 350,148 $ 194,542 $ 240,760 $ 155,420 $ 3,118,392 A summary of nonperforming loans individually evaluated for impairment by category at December 31, 2017 and 2016 , and the income recognized on impaired loans is as follows: December 31, 2017 (in thousands) Unpaid Recorded Recorded Allowance Total Related Allowance Average Commercial and industrial $ 20,750 $ 2,321 $ 10,344 $ 12,665 $ 2,508 $ 16,270 Real estate: Commercial - investor owned 560 422 — 422 — 521 Commercial - owner occupied 487 — 487 487 71 490 Construction and land development 441 136 — 136 — 331 Residential 1,730 1,602 — 1,602 — 1,735 Consumer and other 375 375 — 375 — 375 Total $ 24,343 $ 4,856 $ 10,831 $ 15,687 $ 2,579 $ 19,722 December 31, 2016 (in thousands) Unpaid Recorded Recorded Allowance Total Related Allowance Average Commercial and industrial $ 12,341 $ 566 $ 11,791 $ 12,357 $ 2,909 $ 4,489 Real estate: Commercial - investor owned 525 435 — 435 — 668 Commercial - owner occupied 225 231 — 231 — 227 Construction and land development 1,904 1,947 359 2,306 155 1,918 Residential 62 62 — 62 — 64 Consumer and other — — — — — — Total $ 15,057 $ 3,241 $ 12,150 $ 15,391 $ 3,064 $ 7,366 December 31, (in thousands) 2017 2016 2015 Total interest income that would have been recognized under original terms on impaired loans $ 1,324 $ 1,079 $ 1,038 Total cash received and recognized as interest income on impaired loans 643 251 226 Total interest income recognized on impaired loans still accruing 63 155 36 There were no loans over 90 days past due and still accruing interest at December 31, 2017 or 2016 . The recorded investment in nonperforming loans by category at December 31, 2017 and 2016 , is as follows: December 31, 2017 (in thousands) Non-accrual Restructured, not on non-accrual Total Commercial and industrial $ 11,946 $ 719 $ 12,665 Real estate: Commercial - investor owned 422 — 422 Commercial - owner occupied 487 — 487 Construction and land development 136 — 136 Residential 1,602 — 1,602 Consumer and other 375 — 375 Total $ 14,968 $ 719 $ 15,687 December 31, 2016 (in thousands) Non-accrual Restructured, not on non-accrual Total Commercial and industrial $ 10,046 $ 2,311 $ 12,357 Real estate: Commercial - investor owned 435 — 435 Commercial - owner occupied 231 — 231 Construction and land development 2,286 20 2,306 Residential 62 — 62 Consumer and other — — — Total $ 13,060 $ 2,331 $ 15,391 The recorded investment by category for the portfolio loans that have been restructured during the years ended December 31, 2017 and 2016 , is as follows: Year ended December 31, 2017 Year ended December 31, 2016 (in thousands, except for number of loans) Number of Loans Pre-Modification Outstanding Recorded Balance Post-Modification Outstanding Recorded Balance Number of Loans Pre-Modification Outstanding Recorded Balance Post-Modification Outstanding Recorded Balance Commercial and industrial 1 $ 676 $ 676 4 $ 12,114 $ 12,114 Real estate: Commercial - investor owned — — — 1 248 248 Commercial - owner occupied — — — 1 13 13 Construction and land development — — — 1 20 20 Residential — — — — — — Consumer and other — — — — — — Total 1 $ 676 $ 676 7 $ 12,395 $ 12,395 The restructured portfolio loans primarily resulted from interest rate concessions and changing the terms of the loans. As of December 31, 2017 , the Company allocated no specific reserves to loans that have been restructured. Portfolio loans restructured that subsequently defaulted during the year ended December 31, 2017 , and 2016 , are as follows: Year ended December 31, 2017 Year ended December 31, 2016 (in thousands, except for number of loans) Number of Loans Recorded Balance Number of Loans Recorded Balance Commercial and industrial 2 343 — — Real Estate: Residential 1 5 — — Total 3 348 — — The aging of the recorded investment in past due portfolio loans by portfolio class and category at December 31, 2017 and 2016 is shown below: December 31, 2017 (in thousands) 30-89 Days Past Due 90 or More Past Due Total Past Due Current Total Commercial and industrial $ 7,882 $ 1,770 $ 9,652 $ 1,909,068 $ 1,918,720 Real estate: Commercial - investor owned 934 — 934 768,341 769,275 Commercial - owner occupied — — — 554,589 554,589 Construction and land development 76 — 76 303,015 303,091 Residential 1,529 945 2,474 338,838 341,312 Consumer and other 407 — 407 135,502 135,909 Total $ 10,828 $ 2,715 $ 13,543 $ 4,009,353 $ 4,022,896 December 31, 2016 (in thousands) 30-89 Days Past Due 90 or More Past Due Total Past Due Current Total Commercial and industrial $ 334 $ 171 $ 505 $ 1,632,209 $ 1,632,714 Real estate: Commercial - investor owned — 175 175 544,633 544,808 Commercial - owner occupied 212 225 437 349,711 350,148 Construction and land development 355 1,528 1,883 192,659 194,542 Residential 91 — 91 240,669 240,760 Consumer and other 7 — 7 155,413 155,420 Total $ 999 $ 2,099 $ 3,098 $ 3,115,294 $ 3,118,392 The Company categorizes loans into risk categories based on relevant information about the ability of borrowers to service their debt, such as current financial information, historical payment experience, credit documentation, and current economic factors among other factors. This analysis is performed on a quarterly basis. The Company uses the following definitions for risk ratings: • Grades 1 , 2 , and 3 – Includes loans to borrowers with a continuous record of strong earnings, sound balance sheet condition and capitalization, ample liquidity with solid cash flow, and whose management team has experience and depth within their industry. • Grade 4 – Includes loans to borrowers with positive trends in profitability, satisfactory capitalization and balance sheet condition, and sufficient liquidity and cash flow. • Grade 5 – Includes loans to borrowers that may display fluctuating trends in sales, profitability, capitalization, liquidity, and cash flow. • Grade 6 – Includes loans to borrowers where an adverse change or perceived weakness has occurred, but may be correctable in the near future. Alternatively, this rating category may also include circumstances where the borrower is starting to reverse a negative trend or condition, or has recently been upgraded from a 7 , 8 , or 9 rating. • Grade 7 – Watch credits are borrowers that have experienced financial setback of a nature that is not determined to be severe or influence ‘ongoing concern’ expectations. Although possible, no loss is anticipated, due to strong collateral and/or guarantor support. • Grade 8 – Substandard credits will include those borrowers characterized by significant losses and sustained downward trends in balance sheet condition, liquidity, and cash flow. Repayment reliance may have shifted to secondary sources. Collateral exposure may exist and additional reserves may be warranted. • Grade 9 – Doubtful credits include borrowers that may show deteriorating trends that are unlikely to be corrected. Collateral values may appear insufficient for full recovery, therefore requiring a partial charge-off, or debt renegotiation with the borrower. The borrower may have declared bankruptcy or bankruptcy is likely in the near term. All doubtful rated credits will be on non-accrual. The recorded investment by risk category of the loans by portfolio class and category at December 31, 2017 and December 31, 2016 is as follows: December 31, 2017 (in thousands) Pass (1-6) Watch (7) Substandard (8) Total Commercial and industrial $ 1,769,102 $ 94,002 $ 55,616 $ 1,918,720 Real estate: Commercial - investor owned 754,010 10,840 4,425 769,275 Commercial - owner occupied 514,616 34,440 5,533 554,589 Construction and land development 292,766 9,983 342 303,091 Residential 329,742 3,648 7,922 341,312 Consumer and other 134,704 10 1,195 135,909 Total $ 3,794,940 $ 152,923 $ 75,033 $ 4,022,896 December 31, 2016 (in thousands) Pass (1-6) Watch (7) Substandard (8) Total Commercial and industrial $ 1,499,114 $ 57,416 $ 76,184 $ 1,632,714 Real estate: Commercial - investor owned 530,494 10,449 3,865 544,808 Commercial - owner occupied 306,658 39,249 4,241 350,148 Construction and land development 185,505 6,575 2,462 194,542 Residential 233,479 2,997 4,284 240,760 Consumer and other 153,984 — 1,436 155,420 Total $ 2,909,234 $ 116,686 $ 92,472 $ 3,118,392

Purchased Credit Impaired ("PCI

Purchased Credit Impaired ("PCI") Loans	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Purchased Credit Impaired (PCI) Loans	Below is a summary of PCI loans by category at December 31, 2017 and 2016 : December 31, 2017 December 31, 2016 ($ in thousands) Weighted- Average Risk Rating 1 Recorded Investment PCI Loans Weighted- Average Risk Rating 1 Recorded Investment PCI Loans Commercial and industrial 6.38 $ 3,212 5.87 $ 3,523 Real estate loans: Commercial - investor owned 7.36 42,887 6.95 8,162 Commercial - owner occupied 6.48 11,332 6.39 11,863 Construction and land development 5.99 5,883 5.80 4,365 Residential 5.99 10,781 5.64 11,792 Total real estate loans 70,883 36,182 Consumer and other 2.84 59 1.64 64 Purchased credit impaired loans $ 74,154 $ 39,769 (1) Risk ratings are based on the borrower's contractual obligation, which is not reflective of the purchase discount. The aging of the recorded investment in past due PCI loans by portfolio class and category at December 31, 2017 and 2016 is shown below: December 31, 2017 (in thousands) 30-89 Days Past Due 90 or More Past Due Total Past Due Current Total Commercial and industrial $ — $ — $ — $ 3,212 $ 3,212 Real estate: Commercial - investor owned — 3,034 3,034 39,853 42,887 Commercial - owner occupied — 673 673 10,659 11,332 Construction and land development — — — 5,883 5,883 Residential 328 255 583 10,198 10,781 Consumer and other — — — 59 59 Total $ 328 $ 3,962 $ 4,290 $ 69,864 $ 74,154 December 31, 2016 (in thousands) 30-89 Days Past Due 90 or More Past Due Total Past Due Current Total Commercial and industrial $ — $ — $ — $ 3,523 $ 3,523 Real estate: Commercial - investor owned — — — 8,162 8,162 Commercial - owner occupied — — — 11,863 11,863 Construction and land development — — — 4,365 4,365 Residential 169 51 220 11,572 11,792 Consumer and other — — — 64 64 Total $ 169 $ 51 $ 220 $ 39,549 $ 39,769 The following table is a rollforward of PCI loans, net of the allowance for loan losses, for the years ended December 31, 2017 and 2016 . (in thousands) Contractual Cashflows Non-accretable Difference Accretable Yield Carrying Amount Balance January 1, 2017 $ 66,003 $ 18,902 $ 13,176 $ 33,925 Acquisitions 68,763 14,296 5,312 49,155 Principal reductions and interest payments (24,530 ) — — (24,530 ) Accretion of loan discount — — (7,573 ) 7,573 Changes in contractual and expected cash flows due to remeasurement 13,978 (1,465 ) 5,486 9,957 Reductions due to disposals (11,503 ) (2,727 ) (2,439 ) (6,337 ) Balance December 31, 2017 $ 112,711 $ 29,006 $ 13,962 $ 69,743 Balance January 1, 2016 $ 116,689 $ 26,765 $ 25,341 $ 64,583 Principal reductions and interest payments (25,669 ) — — (25,669 ) Accretion of loan discount — — (6,155 ) 6,155 Changes in contractual and expected cash flows due to remeasurement 11,718 766 (1,500 ) 12,452 Reductions due to disposals (36,735 ) (8,629 ) (4,510 ) (23,596 ) Balance December 31, 2016 $ 66,003 $ 18,902 $ 13,176 $ 33,925 The accretable yield is recognized in interest income over the estimated life of the acquired loans using the effective yield method. Outstanding customer balances on PCI loans were $94.9 million and $54.6 million as of December 31, 2017 , and December 31, 2016 , respectively. On December 7, 2015, the Company entered into an agreement to terminate all existing loss share agreements with the FDIC. Under the terms of the agreement, the FDIC made a net payment to the bank of $1.3 million . The agreement eliminated the FDIC clawback liability of $3.5 million and the FDIC loss share receivable of $7.2 million . Accordingly, a pretax charge of $2.4 million was recorded in 2015 as a separate component of noninterest expense.

Derivative Financial Instrument

Derivative Financial Instruments	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments	DERIVATIVE FINANCIAL INSTRUMENTS The Company is a party to various derivative financial instruments that are used in the normal course of business to meet the needs of its clients and as part of its risk management activities. These instruments include interest rate swaps and option contracts and foreign exchange forward contracts. The Company does not enter into derivative financial instruments for trading purposes. Using derivative instruments can involve assuming counterparty credit risk to varying degrees. Counterparty credit risk relates to the loss the Company could incur if a counterparty were to default on a derivative contract. Notional amounts of derivative financial instruments do not represent credit risk, and are not recorded in the consolidated balance sheet. The overall credit risk and exposure to individual counterparties is monitored. The Company does not anticipate nonperformance by any counterparties. The amount of counterparty credit exposure is the unrealized gains in excess of collateral pledged, if any, on such derivative contracts along with the value of foreign exchange forward contracts. At December 31, 2017 , the Company had $2.1 million of counterparty credit exposure on derivatives. This counterparty risk is considered as part of underwriting and on-going monitoring policies. At December 31, 2017 and 2016 , the Company had pledged cash of $1.4 million and $0.7 million , respectively, as collateral in connection with interest rate swap agreements. Hedging Instruments . At December 31, 2017 , the Company had no outstanding hedging instruments used to manage risk. In the past, the Company entered into interest rate caps in order to economically hedge changes in fair value of certain state tax credits held for sale. See Note 18 – Fair Value Measurements for further discussion of the fair value of the state tax credits. The notional amount of the derivative instruments used to manage risk was $3.5 million at December 31, 2016 . Client-Related Derivative Instruments. The Company enters into interest rate swaps to allow customers to hedge changes in fair value of certain loans while maintaining a variable rate loan on its balance sheet. The Company also enters into foreign exchange forward contracts with clients, and enters into offsetting foreign exchange forward contracts with established financial institution counterparties. The table below summarizes the notional amounts and fair values of the client-related derivative instruments. Asset Derivatives (Other Assets) Liability Derivatives (Other Liabilities) Notional Amount Fair Value Fair Value (in thousands) December 31, December 31, December 31, December 31, December 31, December 31, Non-designated hedging instruments Interest rate swap contracts $ 394,852 $ 124,322 $ 2,061 $ 982 $ 2,061 $ 982 Foreign exchange forward contracts 1,528 3,034 1,528 3,034 1,528 3,034 Changes in the fair value of client-related derivative instruments are recognized currently in operations. For the years ended December 31, 2017 and 2016 , the gains and losses offset each other due to the Company's hedging of the client swaps with other bank counterparties.

Fixed Assets

Fixed Assets	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Fixed Assets	FIXED ASSETS A summary of fixed assets at December 31, 2017 and 2016 , is as follows: December 31, (in thousands) 2017 2016 Land $ 7,263 $ 3,103 Buildings and leasehold improvements 32,384 18,054 Furniture, fixtures and equipment 8,272 6,136 Capitalized software 1,305 1,305 49,224 28,598 Less accumulated depreciation and amortization 16,606 13,688 Total fixed assets $ 32,618 $ 14,910 Depreciation and amortization of fixed assets included in noninterest expense amounted to $3.3 million , $2.4 million , and $2.0 million in 2017 , 2016 , and 2015 , respectively. The Company has facilities leased under agreements that expire in various years through 2029 . The Company's rent expense totaled $3.3 million , $3.1 million , and $3.1 million in 2017 , 2016 , and 2015 , respectively. Sublease rental income was $0.03 million , $0.1 million , and $0.1 million for 2017 , 2016 , and 2015 , respectively. For leases which renew or are subject to periodic rental adjustments, the monthly rental payments will be adjusted based on current market conditions and rates of inflation. The future aggregate minimum rental commitments (in thousands) required under the Company's equipment and facilities leases are shown below: Year Amount 2018 $ 3,503 2019 3,477 2020 3,418 2021 3,337 2022 2,801 Thereafter 5,962 Total $ 22,498 The Company has recorded a liability and corresponding expense for the difference between the net present value of future lease payments and its estimated sublease income on certain vacant branches. As of December 31, 2017 , this liability was $2.0 million . The Company recorded expense for the estimated net lease liability of $0.4 million , $0.5 million , and $0.1 million in 2017 , 2016 , and 2015 , respectively. The expense is recorded within other noninterest expense.

Goodwill and Intangible Assets

Goodwill and Intangible Assets	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	GOODWILL AND INTANGIBLE ASSETS Goodwill increased to $117.3 million as of December 31, 2017 , compared to $30.3 million as of December 31, 2016 due to the acquisition of JCB. The annual goodwill impairment evaluations in 2017 , 2016 , and 2015 did not identify any impairment. The table below presents a summary of intangible assets: (in thousands) Years ended December 31, 2017 2016 Gross core deposit intangible balance, beginning of year $ 9,060 $ 9,060 Additions 11,514 — Gross core deposit intangible, end of period 20,574 9,060 Accumulated amortization (9,518 ) (6,909 ) Core deposit intangible, net, end of year $ 11,056 $ 2,151 Amortization expense on the core deposit intangibles was $2.6 million , $0.9 million , and $1.1 million for the years ended December 31, 2017 , 2016 , and 2015 , respectively. The core deposit intangibles are being amortized over a 10 year period. The following table reflects the expected amortization schedule for the core deposit intangible (in thousands) at December 31, 2017 . Year Core Deposit Intangible 2018 $ 2,504 2019 2,129 2020 1,755 2021 1,381 2022 1,071 After 2022 2,216 $ 11,056

Maturity of Certificates of Dep

Maturity of Certificates of Deposit	12 Months Ended
	Dec. 31, 2017
Maturities of Time Deposits [Abstract]
Maturity of Certificates of Deposit	MATURITY OF CERTIFICATES OF DEPOSIT Following is a summary of certificates of deposit maturities at December 31, 2017 : (in thousands) Brokered Customer Total Less than 1 year $ 114,054 $ 317,373 $ 431,427 Greater than 1 year and less than 2 years 1,252 74,236 75,488 Greater than 2 years and less than 3 years — 48,553 48,553 Greater than 3 years and less than 4 years — 21,100 21,100 Greater than 4 years and less than 5 years — 1,598 1,598 Greater than 5 years — 607 607 $ 115,306 $ 463,467 $ 578,773 Certificates of deposit balances over the FDIC insurance limit of $250,000 were $148.0 million as of December 31, 2017 .

Subordinated Debentures

Subordinated Debentures	12 Months Ended
	Dec. 31, 2017
Subordinated Borrowings [Abstract]
Subordinated Debentures	SUBORDINATED DEBENTURES The amounts and terms of each issuance of the Company's subordinated debentures at December 31, 2017 and 2016 were as follows: Amount Maturity Date Call Date Interest Rate (in thousands) 2017 2016 EFSC Clayco Statutory Trust I $ 3,196 $ 3,196 December 17, 2033 December 17, 2008 Floats 3MO LIBOR + 2.85% EFSC Capital Trust II 5,155 5,155 June 17, 2034 June 17, 2009 Floats 3MO LIBOR + 2.65% EFSC Statutory Trust III 11,341 11,341 December 15, 2034 December 15, 2009 Floats 3MO LIBOR + 1.97% EFSC Clayco Statutory Trust II 4,124 4,124 September 15, 2035 September 15, 2010 Floats 3MO LIBOR + 1.83% EFSC Statutory Trust IV 10,310 10,310 December 15, 2035 December 15, 2010 Floats 3MO LIBOR + 1.44% EFSC Statutory Trust V 4,124 4,124 September 15, 2036 September 15, 2011 Floats 3MO LIBOR + 1.60% EFSC Capital Trust VI 14,433 14,433 March 30, 2037 March 30, 2012 Floats 3MO LIBOR + 1.60% EFSC Capital Trust VII 4,124 4,124 December 15, 2037 December 15, 2012 Floats 3MO LIBOR + 2.25% JEFFCO Stat Trust I (1) 8,153 — February 22, 2031 February 22, 2011 Fixed 10.2% JEFFCO Stat Trust II (1) 4,281 — March 17, 2034 March 17, 2009 Floats 3MO LIBOR + 2.75% Total trust preferred securities 69,241 56,807 Fixed-to-floating rate subordinated notes 50,000 50,000 November 1, 2026 November 1, 2021 Fixed 4.75% until Debt issuance costs (1,136 ) (1,267 ) Total fixed-to-floating rate subordinated notes 48,864 48,733 Total subordinated debentures and notes $ 118,105 $ 105,540 (1) Purchase accounting adjustments are reflected in the balance and also impact the effective interest rate. The Company has 10 unconsolidated statutory business trusts. These trusts issued preferred securities that were sold to third parties. The sole purpose of the trusts was to invest the proceeds in junior subordinated debentures of the Company that have terms identical to the trust preferred securities. The subordinated debentures, which are the sole assets of the trusts, are subordinate and junior in right of payment to all present and future senior and subordinated indebtedness and certain other financial conditions of the Company. The Company fully and unconditionally guarantees each trust's securities obligations. Under current regulations, the trust preferred securities are included in tier 1 capital for regulatory capital purposes, subject to certain limitations. The trust preferred securities are redeemable in whole or in part on or after their respective call dates. Mandatory redemption dates may be shortened if certain conditions are met. The securities are classified as subordinated debentures in the Company's consolidated balance sheets. Interest on the subordinated debentures held by the trusts is recorded as interest expense in the Company's consolidated statements of operations. The Company's investment of $2.1 million at December 31, 2017 , in these trusts is included in other investments in the consolidated balance sheets. On November 1, 2016 , the Company issued $50 million of fixed-to-floating rate subordinated notes. The notes initially bear a fixed annual interest rate of 4.75%, with interest payable semiannually in arrears on May 1 and November 1 of each year, commencing May 1, 2017. Commencing November 1, 2021 , the interest rate on the notes resets quarterly to the three-month LIBOR rate plus a spread of 338.7 basis points, payable quarterly in arrears. On or after November 1, 2021, the Company will have the option to redeem the notes, in whole or in part, at a redemption price equal to 100% of the principal amount of the subordinated notes to be redeemed plus accrued interest, subject to applicable regulatory approval. The Company’s obligation to make payments of principal and interest on the notes is subordinate and junior in right of payment to all of its senior debt. Current regulatory guidance allows for this subordinated debt to be treated as tier 2 regulatory capital for the first five years of its term, subject to certain limitations, and then phased out of tier 2 capital pro rata over the next five years.

Federal Home Loan Bank Advances

Federal Home Loan Bank Advances	12 Months Ended
	Dec. 31, 2017
Investments in and Advances to Affiliates, Schedule of Investments [Abstract]
Federal Home Loan Bank Advances	FEDERAL HOME LOAN BANK ADVANCES FHLB advances are collateralized by 1-4 family residential real estate loans, business loans and certain commercial real estate loans. At December 31, 2017 and 2016 , the carrying value of the loans pledged to the FHLB of Des Moines was $1.1 billion and $773.5 million , respectively. The secured line of credit had availability of approximately $484.7 million at December 31, 2017 . The Company also has an $12.9 million investment in the capital stock of the FHLB of Des Moines at December 31, 2017 . The following table summarizes the type, maturity, and rate of the Company's FHLB advances at December 31: 2017 2016 ($ in thousands) Term Outstanding Balance Weighted Rate Outstanding Balance Weighted Rate Non-amortizing fixed advance Less than 1 year $ 172,743 1.56 % $ — — % Non-amortizing fixed advance Greater than 1 year — — % — — % Total Federal Home Loan Bank Advances $ 172,743 1.56 % $ — — % At December 31, 2017 , the Company used $18.1 million of collateral value to secure confirming letters of credit for public unit deposits and industrial development bonds.

Other Borrowings and Notes Paya

Other Borrowings and Notes Payable	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Other Borrowings and Notes Payable	OTHER BORROWINGS AND NOTES PAYABLE A summary of other borrowings is as follows: December 31, ($ in thousands) 2017 2016 Securities sold under customer repurchase agreements $ 253,674 $ 276,980 Average balance during the year $ 220,807 $ 206,643 Maximum balance outstanding at any month-end 253,674 276,980 Average interest rate during the year 0.21 % 0.19 % Average interest rate at December 31 0.25 % 0.18 % Federal Reserve Line The Bank also has a line with the Federal Reserve Bank of St. Louis which provides additional liquidity to the Company. As of December 31, 2017 , $898.1 million was available under this line. This line is secured by a pledge of certain eligible loans aggregating $1.1 billion . There were no amounts drawn on the Federal Reserve line of credit as of December 31, 2017 . Revolving Credit In February 2016 , the Company entered into a senior unsecured revolving credit agreement ("Revolving Agreement") with another bank allowing for borrowings up to $20 million . The proceeds can be used for general corporate purposes. The Revolving Agreement is subject to ongoing compliance with a number of customary affirmative and negative covenants as well as specified financial covenants. A summary of the amounts drawn on the Revolving Agreement as of December 31, 2017 , and 2016 is as follows: December 31, ($ in thousands) 2017 2016 Outstanding balance $ — $ — Average balance during the year $ 822 $ — Maximum balance outstanding at any month-end 10,000 — Weighted average interest rate during the year 3.50 % — % Average interest rate at December 31 — % — %

Litigation and Other Contingenc

Litigation and Other Contingencies	12 Months Ended
	Dec. 31, 2017
Other Liabilities Disclosure [Abstract]
Litigation and Other Contingencies	LITIGATION AND OTHER CONTINGENCIES The Company and its subsidiaries are, from time to time, parties to various legal proceedings arising out of their businesses. Management believes that there are no such proceedings pending or threatened against the Company or its subsidiaries which, if determined adversely, would have a material adverse effect on the business, consolidated financial condition, results of operations or cash flows of the Company or any of its subsidiaries.

Regulatory Matters

Regulatory Matters	12 Months Ended
	Dec. 31, 2017
Regulated Operations [Abstract]
Regulatory Matters	REGULATORY MATTERS Quantitative measures established by regulation to ensure capital adequacy require the Bank to maintain minimum amounts and ratios (set forth in the following table) of total, tier 1, and common equity tier 1 capital to risk-weighted assets, and of tier 1 capital to average assets. Management believes, as of December 31, 2017 and 2016 , that the Company met all capital adequacy requirements to which it is subject. As of December 31, 2017 and 2016 , the Bank was categorized as “well capitalized” under the regulatory framework for prompt corrective action. To be categorized as “well capitalized” the Bank must maintain minimum total risk-based capital, tier 1 risk-based capital, common equity tier 1 risk-based capital, and tier 1 leverage ratios as set forth in the table. The actual capital amounts and ratios are presented in the table below: Actual For Capital Adequacy Purposes To Be Well Capitalized Under Applicable Action Provisions ($ in thousands) Amount Ratio Amount Ratio Amount Ratio As of December 31, 2017: Total Capital (to Risk Weighted Assets) Enterprise Financial Services Corp $ 589,047 12.21 % $ 385,816 8.00 % $ — — % Enterprise Bank & Trust 546,314 11.36 384,791 8.00 480,989 10.00 Tier 1 Capital (to Risk Weighted Assets) Enterprise Financial Services Corp 496,045 10.29 289,362 6.00 — — Enterprise Bank & Trust 503,312 10.46 288,593 6.00 384,791 8.00 Common Equity Tier 1 Capital (to Risk Weighted Assets) Enterprise Financial Services Corp 428,397 8.88 217,021 4.50 — — Enterprise Bank & Trust 503,264 10.46 216,445 4.50 312,643 6.50 Leverage Ratio (Tier 1 Capital to Average Assets) Enterprise Financial Services Corp 496,045 9.72 204,087 4.00 — — Enterprise Bank & Trust 503,312 9.68 207,885 4.00 259,856 5.00 As of December 31, 2016: Total Capital (to Risk Weighted Assets) Enterprise Financial Services Corp $ 506,349 13.48 % $ 300,573 8.00 % $ — — % Enterprise Bank & Trust 430,981 11.53 298,982 8.00 373,728 10.00 Tier 1 Capital (to Risk Weighted Assets) Enterprise Financial Services Corp 412,865 10.99 225,430 6.00 — — Enterprise Bank & Trust 387,497 10.37 224,237 6.00 298,982 8.00 Common Equity Tier 1 Capital (to Risk Weighted Assets) Enterprise Financial Services Corp 357,729 9.52 169,072 4.50 — — Enterprise Bank & Trust 387,461 10.37 168,178 4.50 242,923 6.50 Leverage Ratio (Tier 1 Capital to Average Assets) Enterprise Financial Services Corp 412,865 10.42 158,480 4.00 — — Enterprise Bank & Trust 387,497 9.81 157,933 4.00 197,417 5.00

Compensation Plans

Compensation Plans	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Compensation Plans	COMPENSATION PLANS The Company has adopted share-based compensation plans to reward and provide long-term incentive for directors and key employees of the Company. These plans provide for the granting of stock, stock options, stock-settled stock appreciation rights ("SSARs"), and restricted stock units (“RSUs”), and may contain performance terms as designated by the Company's Board of Directors upon the recommendation of the Compensation Committee of the Board. The Company uses authorized and unissued shares to satisfy share award exercises. At December 31, 2017 , there were 86,082 shares available for grant under the various share-based compensation plans. Total share-based compensation expense that was charged against income was $3.4 million , $3.4 million , and $3.6 million for the years ended December 31, 2017 , 2016 , and 2015 respectively. The total excess income tax benefit for share-based compensation arrangements was $2.1 million , $1.3 million , and $0.4 million for the years ended December 31, 2017 , 2016 , and 2015 , respectively. Employee Stock Options and Stock-settled Stock Appreciation Rights In determining compensation cost for stock options and SSARs, the Black-Scholes option-pricing model is used to estimate the fair value on date of grant. There were no grants of employee stock options or SSARs during the years ended December 31, 2017 , 2016 , or 2015 . Stock options have been granted to key employees with exercise prices equal to the market price of the Company's common stock at the date of grant and 10 - year contractual terms. Stock options have a vesting schedule of three to five years. The SSARs are subject to continued employment, have a 10 -year contractual term and vest ratably over five years. Neither stock options nor SSARs carry voting or dividend rights until exercised. At December 31, 2017 , there was no remaining unrecognized compensation expense related to stock options and SSARs and all outstanding awards are vested. Various information related to the stock options and SSARs is shown below. (in thousands) 2017 2016 2015 Compensation expense $ — $ — $ 50 Intrinsic value of option exercises on date of exercise 3,156 1,156 74 Cash received from the exercise of stock options 91 87 126 Following is a summary of the employee stock option and SSAR activity for 2017 . (in thousands, except share and per share data) Shares Weighted Weighted Aggregate Outstanding at December 31, 2016 270,246 $ 18.85 Granted — — Exercised (164,116 ) 22.40 Forfeited — — Outstanding at December 31, 2017 106,130 $ 13.37 1.9 years $ 3,373 Exercisable at December 31, 2017 106,130 $ 13.37 1.9 years $ 3,373 Restricted Stock Units The Company awards nonvested stock, in the form of RSUs to employees and directors. RSUs generally are subject to continued employment and vest ratably over two to five years. Vesting is accelerated upon a change in control or the employee meeting certain retirement criteria. RSUs do not carry voting or dividend rights until vested. Sales of the units are restricted prior to vesting. Various information related to the RSUs is shown below. ($ in thousands) 2017 2016 2015 Compensation expense $ 898 $ 850 $ 725 Total fair value at vesting date 1,471 2,275 809 Total unrecognized compensation cost for nonvested stock units 837 1,084 942 Expected years to recognize unearned compensation 1.8 years 1.6 years 1.7 years A summary of the status of the Company's RSU awards as of December 31, 2017 and changes during the year then ended is presented below. Shares Weighted Average Grant Date Fair Value Outstanding at December 31, 2016 58,698 $ 23.06 Granted 16,462 41.68 Vested (33,206 ) 18.48 Forfeited (732 ) 14.48 Outstanding at December 31, 2017 41,222 $ 34.34 Stock Plan for Non-Management Directors The Company has adopted a Stock Plan for Non-Management Directors, which provides for issuing up to 200,000 shares of common stock to non-management directors as compensation in lieu of cash. At December 31, 2017 , there were 19,163 shares of stock available for issuance under the Stock Plan for Non-Management Directors. Various information related to the Director Plan is shown below. (in thousands, except share and per share data) 2017 2016 2015 Shares issued 10,531 12,528 16,283 Weighted average fair value $ 42.46 $ 31.25 $ 24.43 Compensation expense 397 407 373 Employee Stock Issuance Restricted stock was issued to certain key employees as part of their compensation. The restricted stock may be in the form of a one-time award or paid in pro rata installments. The stock is restricted for at least 2 years and upon issuance may be fully vested or vest over 5 years . The Company recognized $0.1 million , zero , and $0.2 million of stock-based compensation expense for the shares issued to the employees in 2017 , 2016 , and 2015 , respectively. The Company issued zero shares in 2017 and 2016 , and 14,110 shares in 2015 . Long-term incentives The Company has entered into long-term incentive agreements with certain key employees. These awards are conditioned on certain performance criteria and market criteria measured against a group of peer banks over a 3 year period for each grant. The awards contain minimum (threshold), target, and maximum (exceptional) performance levels. In the event of a change in control, as defined in the plan, the awards will vest at a minimum of the target level. The amount of the awards are determined at the end of the 3 year vesting and performance period. In January 2018, the Company awarded 134,600 shares to employees upon completion of the 2015-2017 performance cycle. In February 2017, the Company awarded 118,519 shares to employees upon completion of the 2014-2016 performance cycle. In January 2016, the Company awarded 159,094 shares to employees upon completion of the 2013-2015 performance cycle. Information related to the outstanding grants at December 31, 2017 is shown below: (in thousands, except share and per share data) 2016 - 2018 Cycle 2017 - 2019 Cycle Shares issuable at target 87,758 55,203 Maximum shares issuable 107,955 68,263 Unrecognized compensation cost $ 949 $ 1,792 Weighted average grant date fair value 25.26 40.72 The Company recorded $2.5 million , $2.5 million and $2.7 million of stock-based compensation expense for these awards during 2017 , 2016 and 2015 , respectively. In 2017 and 2016, this expense included an additional $0.3 million , and $0.2 million , respectively, related to modifications made for retiring executives. The modification allows for portions of outstanding performance awards to continue to vest as though employment had not terminated and will be paid based on actual performance as determined by the compensation committee following completion of the applicable performance period. 401(k) plans The Company has a 401(k) savings plan which covers substantially all full-time employees over the age of 21 . The amount charged to expense for the Company's contributions to the plan was $2.0 million , $1.7 million and $1.6 million for 2017 , 2016 , and 2015 , respectively.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES The components of income tax expense for the years ended December 31 are as follows: Years ended December 31, (in thousands) 2017 2016 2015 Current: Federal $ 15,845 $ 17,005 $ 22,916 State and local 1,377 1,734 2,798 Total current 17,222 18,739 25,714 Deferred: Federal 20,989 5,959 (5,266 ) State and local 116 1,304 (497 ) Total deferred 21,105 7,263 (5,763 ) Total income tax expense $ 38,327 $ 26,002 $ 19,951 A reconciliation of expected income tax expense, computed by applying the statutory federal income tax rate in 2017 , 2016 , and 2015 to income before income taxes and the amounts reflected in the consolidated statements of operations is as follows: Years ended December 31, (in thousands) 2017 2016 2015 Income tax expense at statutory rate $ 30,281 $ 26,194 $ 20,440 Increase (reduction) in income tax resulting from: Tax-exempt income, net (961 ) (945 ) (931 ) State and local income taxes, net 1,676 1,673 1,414 Bank-owned life insurance, net (715 ) (544 ) (462 ) Non-deductible expenses 407 263 259 Change in estimated rate for deferred taxes 12,117 302 — Tax benefits of LIHTC investments, net (257 ) (181 ) (179 ) Excess tax benefits (2,141 ) — — Other federal tax benefits (1,701 ) — — Other, net (379 ) (760 ) (590 ) Total income tax expense $ 38,327 $ 26,002 $ 19,951 The net amount recognized as a component of tax expense for tax credits, other tax benefits, and amortization from low-income housing tax credit ("LIHTC") investments recognized per the table above was $0.3 million for the year ended December 31, 2017 . The net amount recognized as a component of income tax expense per the table above was $0.2 million for the years ended December 31, 2016 , and 2015 . As of December 31, 2017 and 2016 , the carrying value of the investments related to low-income housing tax credits was $1.3 million and $1.4 million , respectively. No impairment losses have been recognized from forfeiture or ineligibility of tax credits or other circumstances during the life of any of the investments. As of December 31, 2017 , the Company has future capital commitments of $4.8 million related to low-income housing tax credit investments. The capital commitments are expected to be called between the years 2018 - 2020. A net deferred income tax asset of $22.5 million and $33.8 million is included in other assets in the consolidated balance sheets at December 31, 2017 and 2016 , respectively. The tax effect of temporary differences that gave rise to significant portions of the deferred tax assets and deferred tax liabilities is as follows: Years ended December 31, (in thousands) 2017 2016 Deferred tax assets: Allowance for loan losses $ 10,516 $ 16,496 Basis difference on PCI assets, net 5,748 5,551 Basis difference on Other real estate 694 317 Deferred compensation 2,719 4,217 Goodwill and other intangible assets 2,151 5,520 Accrued compensation 646 899 Unrealized losses on securities available for sale 1,490 1,019 Other, net 2,150 925 Total deferred tax assets 26,114 34,944 Deferred tax liabilities: State tax credits held for sale, net of economic hedge 26 376 Core deposit intangibles 2,731 817 Other, net 855 — Total deferred tax liabilities 3,612 1,193 Net deferred tax asset $ 22,502 $ 33,751 Deferred tax rate 24.7 % 38.0 % Net deferred tax assets for the year ended December 31, 2017, experienced an increase of $8.6 million from the acquisition of JCB, offset by a revaluation adjustment of $12.1 million due to our initial analysis of the impact of the Tax Act. A valuation allowance is provided on deferred tax assets when it is more likely than not that some portion of the assets will not be realized. The Company did not have any valuation allowances for federal or state income taxes as of December 31, 2017 or 2016 . The Company and its subsidiaries file income tax returns in the federal jurisdiction and in nine states. The Company is no longer subject to federal, state or local income tax audits by tax authorities for years before 2014, with the exception of 2013 being an open year by one state taxing authority. The Company is not currently under audit by any taxing jurisdiction. As of December 31, 2017 , the gross amount of unrecognized tax benefits was $1.2 million and the total amount of net unrecognized tax benefits that would impact the effective tax rate, if recognized, was $0.8 million . As of December 31, 2016 and 2015 , the total amount of the net unrecognized tax benefits that would impact the effective tax rate, if recognized, was $0.8 million and $0.9 million , respectively. The Company believes it is reasonably possible that the gross amount of unrecognized benefits will be reduced by approximately $0.3 million as a result of a lapse of statute of limitations in the next 12 months. The Company recognizes interest and penalties related to uncertain tax positions in income tax expense and classifies such interest and penalties in the liability for unrecognized tax benefits. The amounts accrued for interest and penalties as of December 31, 2017 , 2016 , and 2015 were not significant. The activity in the gross liability for unrecognized tax benefits was as follows: (in thousands) 2017 2016 2015 Balance at beginning of year $ 1,180 $ 1,359 $ 1,884 Additions based on tax positions related to the current year 331 239 230 Additions for tax positions of prior years 41 39 46 Reductions for tax positions of prior years — — (437 ) Settlements or lapse of statute of limitations (308 ) (457 ) (364 ) Balance at end of year $ 1,244 $ 1,180 $ 1,359

Commitments

Commitments	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments	COMMITMENTS The Company issues financial instruments in the normal course of the business of meeting the financing needs of its customers. These financial instruments include commitments to extend credit and standby letters of credit. These instruments may involve, to varying degrees, elements of credit and interest rate risk in excess of the amounts recognized in the consolidated balance sheets. The Company’s extent of involvement and maximum potential exposure to credit loss in the event of nonperformance by the other party to the financial instrument for commitments to extend credit and standby letters of credit is not more than the contractual amount of these instruments. The Company uses the same credit policies in making commitments and conditional obligations as it does for financial instruments included on its consolidated balance sheets. The contractual amounts of off-balance-sheet financial instruments as of December 31, 2017 , and December 31, 2016 , are as follows: (in thousands) December 31, 2017 December 31, 2016 Commitments to extend credit $ 1,298,423 $ 1,075,170 Letters of credit 73,790 78,954 There was an insignificant amount of unadvanced commitments on impaired loans at December 31, 2017 and December 31, 2016 . Other liabilities include approximately $0.4 million for estimated losses attributable to the unadvanced commitments. Commitments to extend credit are agreements to lend to a customer as long as there is no violation of any condition established in the contract. Commitments usually have fixed expiration dates or other termination clauses, may have significant usage restrictions, and may require payment of a fee. Of the total commitments to extend credit at December 31, 2017 , and December 31, 2016 , $112.0 million and $89.7 million , respectively, represent fixed rate loan commitments. Since certain of the commitments may expire without being drawn upon or may be revoked, the total commitment amounts do not necessarily represent future cash obligations. The Company evaluates each customer’s credit worthiness on a case-by-case basis. The amount of collateral obtained, if deemed necessary by the Company upon extension of credit, is based on management’s credit evaluation of the borrower. Collateral held varies, but may include accounts receivable, inventory, premises and equipment, and real estate. Letters of credit are conditional commitments issued by the Company to guarantee the performance of a customer to a third party. These letters of credit are issued to support contractual obligations of the Company’s customers. The credit risk involved in issuing letters of credit is essentially the same as the risk involved in extending loans to customers. The approximate remaining term of letters of credit range from 1 month to 3 years and 9 months at December 31, 2017 .

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	FAIR VALUE MEASUREMENTS The fair value of an asset or liability is the price that would be received to sell that asset or paid to transfer that liability in an orderly transaction occurring in the principal market (or most advantageous market in the absence of a principal market) for such asset or liability. In estimating fair value, the Company utilizes valuation techniques that are consistent with the market approach, the income approach and/or the cost approach. Such valuation techniques are consistently applied. Inputs to valuation techniques include the assumptions that market participants would use in pricing an asset or liability. ASC Topic 820, Fair Value Measurements and Disclosures, establishes a fair value hierarchy for valuation inputs that gives the highest priority to quoted prices in active markets for identical assets or liabilities and the lowest priority to unobservable inputs. The fair value hierarchy is as follows: • Level 1 Inputs - Unadjusted quoted prices in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. • Level 2 Inputs - Inputs other than quoted prices included in Level 1 that are observable for the asset or liability, either directly or indirectly. These might include quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability (such as interest rates, volatilities, prepayment speeds, credit risks, etc.) or inputs that are derived principally from or corroborated by market data by correlation or other means. • Level 3 Inputs - Unobservable inputs for determining the fair values of assets or liabilities that reflect an entity's own assumptions about the assumptions that market participants would use in pricing the assets or liabilities. Fair value on a recurring basis The following table summarizes financial instruments measured at fair value on a recurring basis as of December 31, 2017 and 2016 , segregated by the level of the valuation inputs within the fair value hierarchy utilized to measure fair value. December 31, 2017 (in thousands) Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Fair Value Assets Securities available for sale Obligations of U.S. Government-sponsored enterprises $ — $ 99,224 $ — $ 99,224 Obligations of states and political subdivisions — 34,642 — 34,642 Residential mortgage-backed securities — 507,516 — 507,516 Total securities available for sale — 641,382 — 641,382 State tax credits held for sale — — 400 400 Derivative financial instruments — 3,589 — 3,589 Total assets $ — $ 644,971 $ 400 $ 645,371 Liabilities Derivative financial instruments $ — $ 3,589 $ — $ 3,589 Total liabilities $ — $ 3,589 $ — $ 3,589 December 31, 2016 (in thousands) Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Fair Value Assets Securities available for sale Obligations of U.S. Government-sponsored enterprises $ — $ 107,660 $ — $ 107,660 Obligations of states and political subdivisions — 33,542 3,089 36,631 Residential mortgage-backed securities — 316,506 — 316,506 Total securities available for sale — 457,708 3,089 460,797 State tax credits held for sale — — 3,585 3,585 Derivative financial instruments — 4,016 — 4,016 Total assets $ — $ 461,724 $ 6,674 $ 468,398 Liabilities Derivative financial instruments $ — $ 4,016 $ — $ 4,016 Total liabilities $ — $ 4,016 $ — $ 4,016 • Securities available for sale . Securities classified as available for sale are reported at fair value utilizing Level 2 and Level 3 inputs. Fair values for Level 2 securities are based upon dealer quotes, market spreads, the U.S. Treasury yield curve, trade execution data, market consensus prepayment speeds, credit information and the bond's terms and conditions at the security level. At December 31, 2017 , there were no Level 3 Auction Rate Securities. Auction Rate Securities at December 31, 2017 were valued using a Level 2 pricing source similar to our other securities available for sale. • State tax credits held for sale. At December 31, 2017 , of the $43.5 million of state tax credits held for sale on the consolidated balance sheet, approximately $0.4 million were carried at fair value. The remaining $43.1 million of state tax credits were accounted for at cost. The Company elected not to account for the state tax credits purchased since 2010 at fair value in order to limit the volatility of the fair value changes in our consolidated statements of operations. The Company is not aware of an active market that exists for the 10 -year streams of state tax credit financial instruments. However, the Company’s principal market for these tax credits consists of Missouri state residents who buy these credits and local and regional accounting firms who broker them. As such, the Company employed a discounted cash flow analysis (income approach) to determine the fair value. The fair value measurement is calculated using an internal valuation model with market data including discounted cash flows based upon the terms and conditions of the tax credits. If the underlying project remains in compliance with the various federal and state rules governing the tax credit program, each project will generate about 10 years of tax credits. The inputs to the discounted cash flow calculation include: the amount of tax credits generated each year, the anticipated sale price of the tax credit, the timing of the sale and a discount rate. The discount rate is estimated using the LIBOR swap curve at a point equal to the remaining life in years of credits plus a 205 basis point spread. With the exception of the discount rate, the other inputs to the fair value calculation are observable and readily available. The discount rate is considered a Level 3 input because it is an “unobservable input” and is based on the Company’s assumptions. An increase in the discount rate utilized would generally result in a lower estimated fair value of the tax credits. Alternatively, a decrease in the discount rate utilized would generally result in a higher estimated fair value of the tax credits. Given the significance of this input to the fair value calculation, the state tax credit assets are reported as Level 3 assets. • Derivatives . Derivatives are reported at fair value utilizing Level 2 inputs. The Company obtains counterparty quotations to value its interest rate swaps and caps. In addition, the Company validates the counterparty quotations with third party valuation sources. Derivatives with negative fair values are included in Other liabilities in the consolidated balance sheets. Derivatives with positive fair value are included in Other assets in the consolidated balance sheets. Level 3 financial instruments The following table presents the changes in Level 3 financial instruments measured at fair value on a recurring basis as of December 31, 2017 and 2016 . • Purchases, sales, issuances and settlements . There were no Level 3 purchases during the years ended December 31, 2017 and 2016 . • Transfers in and/or out of Level 3 . There was $3.1 million in Level 3 transfers to Level 2 for the year ending December 31, 2017 because more observable market data became available for the Auction Rate Securities. The Company's policy is to recognize transfers into or out of a level as of the end of a reporting period. As a result, the transfers occurred on June 30, 2017. There were no transfers in and/or out of Level 3 for the year ending 2016 . Securities available for sale, at fair value Years ended December 31, (in thousands) 2017 2016 Beginning balance $ 3,089 $ 3,077 Total gains: Included in other comprehensive income 4 12 Transfer in and/or out of Level 3 (3,093 ) — Ending balance $ — $ 3,089 Change in unrealized gains relating to assets still held at the reporting date $ — $ 12 State tax credits held for sale, at fair value Years ended December 31, (in thousands) 2017 2016 Beginning balance $ 3,585 $ 5,941 Total gains: Included in earnings 101 177 Purchases, sales, issuances and settlements: Sales (3,286 ) (2,533 ) Ending balance $ 400 $ 3,585 Change in unrealized losses relating to assets still held at the reporting date $ (885 ) $ (575 ) Fair value on a non-recurring basis Certain financial assets and financial liabilities are measured at fair value on a non-recurring basis; that is, the instruments are not measured at fair value on an ongoing basis but are subject to fair value adjustments in certain circumstances (for example, when there is evidence of impairment). • Impaired loans . Impaired loans are included as Portfolio loans on the Company's consolidated balance sheets with amounts specifically reserved for credit impairment in the Allowance for loan losses. On a quarterly basis, fair value adjustments are recorded on impaired loans to account for (1) partial write-downs that are based on the current appraised or market-quoted value of the underlying collateral or (2) the full charge-off of the loan carrying value. In some cases, the properties for which market quotes or appraised values have been obtained are located in areas where comparable sales data is limited, outdated, or unavailable. In addition, the Company may adjust the valuations based on other relevant market conditions or information. Accordingly, fair value estimates, including those obtained from real estate brokers or other third-party consultants, for collateral-dependent impaired loans are classified in Level 3 of the valuation hierarchy. • Other Real Estate. These assets are reported at the lower of the loan carrying amount at foreclosure or fair value. Fair value is based on third party appraisals of each property and the Company's judgment of other relevant market conditions. These are considered Level 3 inputs. The following table presents financial instruments and non-financial assets measured at fair value on a non-recurring basis as of December 31, 2017 and 2016 . December 31, 2017 (1) (1) (1) (1) (in thousands) Total Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant (Level 3) Total losses for the year ended Impaired loans $ 3,200 $ — $ — $ 3,200 $ 6,599 Other real estate — — — — — Total $ 3,200 $ — $ — $ 3,200 $ 6,599 December 31, 2016 (1) (1) (1) (1) (in thousands) Total Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant (Level 3) Total losses for the year ended Impaired loans $ 175 $ — $ — $ 175 $ 4,335 Other real estate — — — — 1 Total $ 175 $ — $ — $ 175 $ 4,336 (1) The amounts represent only balances measured at fair value during the period and still held as of the reporting date. Impaired loans are reported at the fair value of the underlying collateral. Fair values for impaired loans are obtained from current appraisals by qualified licensed appraisers or independent valuation specialists. Other real estate owned is adjusted to fair value upon foreclosure of the underlying loan. Subsequently, foreclosed assets are carried at the lower of carrying value or fair value less costs to sell. Fair value of other real estate is based upon the current appraised values of the properties as determined by qualified licensed appraisers and the Company’s judgment of other relevant market conditions. Certain state tax credits are reported at cost. Carrying amount and fair value at December 31, 2017 and 2016 Following is a summary of the carrying amounts and fair values of the Company’s financial instruments on the consolidated balance sheets at December 31, 2017 and 2016 . December 31, 2017 December 31, 2016 (in thousands) Carrying Amount Estimated fair value Carrying Amount Estimated fair value Balance sheet assets Cash and due from banks $ 91,084 $ 91,084 $ 54,288 $ 54,288 Federal funds sold 1,223 1,223 446 446 Interest-bearing deposits 63,661 63,661 145,048 145,048 Securities available for sale 641,382 641,382 460,797 460,797 Securities held to maturity 73,749 73,458 80,463 79,639 Other investments, at cost 26,661 26,661 14,840 14,840 Loans held for sale 3,155 3,155 9,562 9,562 Derivative financial instruments 3,589 3,589 4,016 4,016 Portfolio loans, net 4,054,473 4,096,741 3,114,752 3,125,701 State tax credits, held for sale 43,468 44,271 38,071 41,264 Accrued interest receivable 14,069 14,069 11,117 11,117 Balance sheet liabilities Deposits 4,156,414 4,153,323 3,233,361 3,232,414 Subordinated debentures and notes 118,105 105,031 105,540 86,052 Federal Home Loan Bank advances 172,743 172,893 — — Other borrowings 253,674 253,530 276,980 276,905 Derivative financial instruments 3,589 3,589 4,016 4,016 Accrued interest payable 1,730 1,730 1,105 1,105 The following table presents the level in the fair value hierarchy for the estimated fair values of only the Company’s financial instruments that are not already on the consolidated balance sheets at fair value at December 31, 2017 , and December 31, 2016 . Estimated Fair Value Measurement at Reporting Date Using Balance at (in thousands) Level 1 Level 2 Level 3 Financial Assets: Securities held to maturity $ — $ 73,458 $ — $ 73,458 Portfolio loans, net — — 4,096,741 4,096,741 State tax credits, held for sale — — 43,871 43,871 Financial Liabilities: Deposits 3,577,641 — 575,682 4,153,323 Subordinated debentures and notes — 105,031 — 105,031 Federal Home Loan Bank advances — 172,893 — 172,893 Other borrowings — 253,530 — 253,530 Estimated Fair Value Measurement at Reporting Date Using Balance at (in thousands) Level 1 Level 2 Level 3 Financial Assets: Securities held to maturity $ — $ 79,639 $ — $ 79,639 Portfolio loans, net — — 3,125,701 3,125,701 State tax credits, held for sale — — 37,679 37,679 Financial Liabilities: Deposits 2,760,202 — 472,212 3,232,414 Subordinated debentures and notes — 86,052 — 86,052 Federal Home Loan Bank advances — — — — Other borrowings — 276,905 — 276,905 The following methods and assumptions were used to estimate the fair value of each class of financial instruments for which it is practical to estimate such value: Cash, Federal funds sold, and other short-term instruments For cash and due from banks, federal funds purchased, interest-bearing deposits, and accrued interest receivable (payable), the carrying amount is a reasonable estimate of fair value, as such instruments reprice in a short time period (Level 1). Securities available for sale and held to maturity The Company obtains fair value measurements for debt instruments from an independent pricing service. The fair value measurements consider observable data that may include dealer quotes, market spreads, cash flows, the U.S. Treasury yield curve, live trading levels, trade execution data, market consensus prepayment speeds, credit information and the bond's terms and conditions (Level 2). Other investments Other investments, which primarily consists of membership stock in the FHLB, is reported at cost, which approximates fair value (Level 2). Loans held for sale These loans consist of mortgages that are sold on the secondary market generally within three months of origination. They are reported at cost, which approximates fair value (Level 2). Portfolio loans, net The fair value of adjustable-rate loans approximates cost. The fair value of fixed-rate loans is estimated by discounting the future cash flows using the current rates at which similar loans would be made to borrowers for the same remaining maturities. The fair value of the acquired loans are based on the present value of expected future cash flows (Level 3). The method of estimating fair value does not incorporate the exit-price concept of fair value prescribed by ASC Topic 820. State tax credits held for sale The fair value of state tax credits held for sale is calculated using an internal valuation model with unobservable market data as discussed in further detail above (Level 3). Derivative financial instruments The fair value of derivative financial instruments is based on quoted market prices by the counterparty and verified by the Company using public pricing information (Level 2). Deposits The fair value of demand deposits, interest-bearing transaction accounts, money market accounts and savings deposits is the amount payable on demand at the reporting date (Level 1). The fair value of fixed-maturity certificates of deposit is estimated by discounting the future cash flows using the rates currently offered for deposits of similar remaining maturities (Level 3). Subordinated debentures and notes Fair value of subordinated debentures and notes is based on discounting the future cash flows using rates currently offered for financial instruments of similar remaining maturities (Level 2). Federal Home Loan Bank advances The fair value of the FHLB advances is based on the discounted value of contractual cash flows. The discount rate is estimated using current rates on borrowed money with similar remaining maturities (Level 2). Other borrowed funds Other borrowed funds include customer repurchase agreements, federal funds purchased, notes payable, and secured borrowings related to loan participations. The fair value of federal funds purchased, customer repurchase agreements and notes payable are assumed to be equal to their carrying amount since they have an adjustable interest rate (Level 2). Commitments to extend credit and letters of credit The fair value of commitments to extend credit and letters of credit are estimated using the fees currently charged to enter into similar agreements, taking into account the remaining terms of the agreements, the likelihood of the counterparties drawing on such financial instruments, and the present creditworthiness of such counterparties (Level 2). The Company believes such commitments have been made on terms which are competitive in the markets in which it operates; however, no premium or discount is offered thereon and accordingly, the Company has not assigned a value to such instruments for purposes of this disclosure. Limitations Fair value estimates are made at a specific point in time, based on relevant market information and information about the financial instrument. These estimates are subjective in nature and involve uncertainties and matters of significant judgment, and therefore, cannot be determined with precision. Such estimates include the valuation of loans, goodwill, intangible assets, and other long-lived assets, along with assumptions used in the calculation of income taxes, among others. These estimates and assumptions are based on management's best estimates and judgment. Management evaluates its estimates and assumptions on an ongoing basis using experience and other factors, including the current economic environment, which management believes to be reasonable under the circumstances. We adjust such estimates and assumptions when facts and circumstances dictate. Decreasing real estate values, illiquid credit markets, volatile equity markets, and declines in consumer spending have combined to increase the uncertainty inherent in such estimates and assumptions. As future events and their effects cannot be determined with precision, actual results could differ significantly from these estimates. Changes in estimates resulting from continuing changes in the economic environment will be reflected in the financial statement in future periods. In addition, these estimates do not reflect any premium or discount that could result from offering for sale at one time the Company's entire holdings of a particular financial instrument. Fair value estimates are based on existing on-balance and off-balance-sheet financial instruments without attempting to estimate the value of anticipated future business and the value of assets and liabilities that are not considered financial instruments. In addition, the tax ramifications related to the realization of the unrealized gains and losses can have a significant effect on fair value estimates and have not been considered in many of the estimates.

Parent Company Only Condensed F

Parent Company Only Condensed Financial Statements	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Parent Company Only Condensed Financial Statements	PARENT COMPANY ONLY CONDENSED FINANCIAL STATEMENTS Condensed Balance Sheets December 31, (in thousands) 2017 2016 Assets Cash $ 9,977 $ 52,245 Investment in Enterprise Bank & Trust 623,439 416,831 Investment in nonbank subsidiaries 6,546 2,798 Other assets 28,741 22,111 Total assets $ 668,703 $ 493,985 Liabilities and Shareholders' Equity Subordinated debentures and notes $ 118,105 $ 105,540 Accounts payable and other liabilities 2,025 1,347 Shareholders' equity 548,573 387,098 Total liabilities and shareholders' equity $ 668,703 $ 493,985 Condensed Statements of Operations Years ended December 31, (in thousands) 2017 2016 2015 Income: Dividends from subsidiaries $ 20,000 $ 7,500 $ 10,000 Other 708 491 249 Total income 20,708 7,991 10,249 Expenses: Interest expense-subordinated debentures and notes 5,094 1,893 1,248 Interest expense-notes payable 89 53 144 Other expenses 5,486 5,526 3,823 Total expenses 10,669 7,472 5,215 Income before taxes and equity in undistributed earnings of subsidiaries 10,039 519 5,034 Income tax benefit 3,098 2,583 2,118 Net income before equity in undistributed earnings of subsidiaries 13,137 3,102 7,152 Equity in undistributed earnings of subsidiaries 35,053 45,735 31,298 Net income and comprehensive income $ 48,190 $ 48,837 $ 38,450 Condensed Statements of Cash Flows Years Ended December 31, (in thousands) 2017 2016 2015 Cash flows from operating activities: Net income $ 48,190 $ 48,837 $ 38,450 Adjustments to reconcile net income to net cash provided by (used in) operating activities: Share-based compensation 3,427 3,367 3,601 Net income of subsidiaries (55,053 ) (53,235 ) (41,298 ) Dividends from subsidiaries 20,000 7,500 10,000 Excess tax expense of share-based compensation — (1,327 ) (449 ) Other, net (1,806 ) 1,848 848 Net cash provided by operating activities 14,758 6,990 11,152 Cash flows from investing activities: Cash contributions to subsidiaries — (250 ) — Cash paid for acquisitions, net of cash acquired (25,187 ) — — Purchases of other investments (3,679 ) (2,435 ) (2,832 ) Proceeds from distributions on other investments 1,634 1,151 880 Net cash used by investing activities (27,232 ) (1,534 ) (1,952 ) Cash flows from financing activities: Proceeds from issuance of subordinated notes — 48,733 — Proceeds from notes payable 10,000 — — Repayments of notes payable (10,000 ) — (5,700 ) Cash dividends paid (10,249 ) (8,211 ) (5,259 ) Excess tax benefit of share-based compensation — 1,327 449 Payments for the repurchase of common stock (16,636 ) (4,889 ) — Payments for the issuance of equity instruments, net (2,909 ) (2,203 ) (1,190 ) Net cash provided (used) by financing activities (29,794 ) 34,757 (11,700 ) Net increase (decrease) in cash and cash equivalents (42,268 ) 40,213 (2,500 ) Cash and cash equivalents, beginning of year 52,245 12,032 14,532 Cash and cash equivalents, end of year $ 9,977 $ 52,245 $ 12,032 Supplemental disclosures of cash flow information: Noncash transactions: Common shares issued in connection with JCB acquisition $ 141,729 $ — $ —

Quarterly Condensed Financial I

Quarterly Condensed Financial Information	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Condensed Financial Information	QUARTERLY CONDENSED FINANCIAL INFORMATION (Unaudited) The following table presents unaudited quarterly financial information for the periods indicated: 2017 (in thousands, except per share data) 4th Quarter 3rd Quarter 2nd Quarter 1st Quarter Interest income $ 54,789 $ 52,468 $ 51,542 $ 43,740 Interest expense 7,385 6,843 5,909 5,098 Net interest income 47,404 45,625 45,633 38,642 Provision for portfolio loan losses 3,186 2,422 3,623 1,533 Provision reversal for purchased credit impaired loan losses (279 ) — (207 ) (148 ) Net interest income after provision for loan losses 44,497 43,203 42,217 37,257 Noninterest income 11,112 8,372 7,934 6,976 Noninterest expense 28,260 27,404 32,651 26,736 Income before income tax expense 27,349 24,171 17,500 17,497 Income tax expense 19,820 7,856 5,545 5,106 Net income $ 7,529 $ 16,315 $ 11,955 $ 12,391 Earnings per common share: Basic $ 0.33 $ 0.70 $ 0.51 $ 0.57 Diluted 0.32 0.69 0.50 0.56 2016 (in thousands, except per share data) 4th Quarter 3rd Quarter 2nd Quarter 1st Quarter Interest income $ 39,438 $ 37,293 $ 37,033 $ 35,460 Interest expense 3,984 3,463 3,250 3,032 Net interest income 35,454 33,830 33,783 32,428 Provision for portfolio loan losses 964 3,038 716 833 Provision reversal for purchased credit impaired loan losses (343 ) (1,194 ) (336 ) (73 ) Net interest income after provision for loan losses 34,833 31,986 33,403 31,668 Noninterest income 9,029 6,976 7,049 6,005 Noninterest expense 23,181 20,814 21,353 20,762 Income before income tax expense 20,681 18,148 19,099 16,911 Income tax expense 7,053 6,316 6,747 5,886 Net income $ 13,628 $ 11,832 $ 12,352 $ 11,025 Earnings per common share: Basic $ 0.68 $ 0.59 $ 0.62 $ 0.55 Diluted 0.67 0.59 0.61 0.54

New Authoritative Accounting Gu

New Authoritative Accounting Guidance	12 Months Ended
	Dec. 31, 2017
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
New Authoritative Accounting Guidance	NEW AUTHORITATIVE ACCOUNTING GUIDANCE Financial Accounting Standards Board (the "FASB") Accounting Standards Update (the "ASU") 2018-02 "Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income" In February 2018, the FASB issued ASU 2018-02, "Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income". The amendment allow a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act. Entities will be able to early adopt the guidance in any interim or annual period for which financial statements have not yet been issued and apply it either (1) in the period of adoption or (2) retrospectively to each period in which the effect of the change in the federal income tax rate in the Tax Cuts and Jobs Act is recognized. It would also allow entities to elect to reclassify other stranded tax effects that relate to the Act but do not directly relate to the change in the federal rate (e.g., state taxes, changing from a worldwide tax system to a territorial system). Tax effects that are stranded in OCI for other reasons (e.g., prior changes in tax law, a change in valuation allowance) may not be reclassified. The Company plans to adopt this standard in the first quarter of 2018, and apply it to the same period. The adoption of this update will result in an increase to retained earnings of $0.8 million being reclassified from accumulated other comprehensive income. FASB ASU 2017-12 "Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities" In August 2017, the FASB issued ASU 2017-12, "Targeted Improvement to Accounting for Hedging Activities". The objective of ASU 2017-12 is to improve the financial reporting of hedging relationships by better aligning an entity's risk management activity with the economic objectives in undertaking those activities. In addition, the amendments in this update simplify the application of hedge accounting for preparers of financial statements, as well as improve the understandability of an entity's risk management activities being conveyed to financial statement users. The new guidance becomes effective for periods beginning after December 15, 2018, with early adoption being permitted. The Company elected early adoption of this standard as of January 1, 2018. The effect of this adoption will have a minimal impact on the Company's consolidated financial statements. FASB ASU 2017-09 "Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting" In May 2017, the FASB issued ASU 2017-09, "Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting" which amends the scope of modification accounting for share-based payment awards. The amendments provide guidance on the types of changes to the terms or conditions of share-based payment awards to which an entity would be required to apply modification accounting with an intent to simplify the accounting under ASC 718. The amendments are effective for public business entities for annual periods beginning after December 15, 2017, including interim periods within those annual periods, with early adoption being permitted. The Company has evaluated the new guidance and does not expect it to have a material impact on the Company's consolidated financial statements. FASB ASU 2017-08 "Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20), Premium Amortization on Purchased Callable Debt Securities" In March 2017, the FASB issued ASU 2017-08, "Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20)" which shortens the amortization period of certain callable debt securities held at a premium to the earliest call date. The amendments are effective for public business entities for annual periods beginning after December 15, 2018, including interim periods within those annual periods, with early adoption being permitted. The Company is currently evaluating the new guidance and has not determined the impact this standard may have on its financial statements. FASB ASU 2016-13 "Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments" In June 2016, the FASB issued ASU 2016-13, "Financial Instruments (Topic 326)" which changes the methodology for evaluating impairment of most financial instruments. The ASU replaces the currently used incurred loss model with a forward-looking expected loss model, which will generally result in a more timely recognition of losses. The guidance becomes effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. The Company is currently evaluating the new guidance and has not determined the impact this standard may have on its financial statements. FASB ASU 2016-02 "Leases (Topic 842)" In February 2016, the FASB issued ASU 2016-02, "Leases (Topic 842)" which requires organizations that lease assets ("lessees") to recognize the assets and liabilities for the rights and obligations created by leases with terms of more than 12 months. The recognition, measurement, and presentation of expenses and cash flows arising from a lease by a lessee remains dependent on its classification as a finance or operating lease. The criteria for determining whether a lease is a finance or operating lease has not been significantly changed by this ASU. The ASU also requires additional disclosure of the amount, timing, and uncertainty of cash flows arising from leases, including qualitative and quantitative requirements. The guidance becomes effective for periods beginning after December 15, 2018, including interim periods therein. Early adoption will be permitted. The adoption of this standard will gross up the Company's Consolidated Balance Sheet and utilize capital, but it will have no impact on the Consolidated Statements of Operations. FASB ASU 2016-01 "Financial Instruments-Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities" In January 2016, the FASB issued ASU 2016-01, "Financial Instruments-Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities." ASU 2016-01 requires equity investments to be measured at fair value through earnings, and eliminates the available-for-sale classification for equity securities with readily determinable fair values. For financial liabilities where the fair value option has been elected, changes in fair value due to instrument-specific credit risk must be recognized in other comprehensive income. When measuring the fair value of financial instruments at amortized cost, the exit price must be used for disclosure purposes. The ASU also requires that financial assets and liabilities be presented separately in the notes to the financial statements. This ASU becomes effective for fiscal years beginning after December 15, 2017, including interim periods therein. Early adoption is permitted with some exceptions. The Company has evaluated its applicable equity investments and determined that they primarily qualify for the measurement exception which allows those investments to be measured at their cost minus impairment. Any valuation adjustments will be recorded prospectively through net income, and the related disclosure will be included in the Notes to the Consolidated Financial Statements. FASB ASU 2014-09, "Revenue from Contracts with Customers (Topic 606)" In May 2014, the FASB issued ASU 2014-09, “Revenue from Contracts with Customers”. The objective of ASU 2014-09 is to establish a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and will supersede most of the existing revenue recognition guidance, including industry-specific guidance. The core principle of ASU 2014-09 is that an entity recognizes revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In applying the new guidance, an entity will (1) identify the contract(s) with a customer; (2) identify the performance obligations in the contract; (3) determine the transaction price; (4) allocate the transaction price to the contract’s performance obligations; and (5) recognize revenue when (or as) the entity satisfies a performance obligation. ASU 2014-09 applies to all contracts with customers except those that are within the scope of other topics in the FASB Accounting Standards Codification. In August 2015, the FASB issued ASU 2015-14, which defers the effective date of this guidance to annual reporting periods beginning after December 15, 2017 for public companies, and permits early adoption on a limited basis. The Company has conducted its initial assessment and is currently evaluating contracts to assess and quantify accounting methodology changes resulting from the adoption of ASU 2014-09. The majority of the Company’s revenues are derived from loans which are excluded from the new standard; therefore, the new guidance is not expected to have a material impact on the Company's consolidated financial position, results of operations or cash flows. The Company has decided upon the modified retrospective adoption method.

Summary of Significant Accoun32

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Business and Consolidation	Enterprise Financial Services Corp and subsidiaries (the “Company” or “Enterprise”) is a financial holding company that provides a full range of banking and wealth management services to individuals and corporate customers primarily located in the St. Louis, Kansas City, and Phoenix metropolitan markets through its banking subsidiary, Enterprise Bank & Trust (the “Bank”). The consolidated financial statements include the accounts of the Company, and its subsidiaries, all of which are wholly owned. All intercompany accounts and transactions have been eliminated. The Company is subject to competition from other financial and nonfinancial institutions providing financial services in the markets served by the Company's subsidiary. Additionally, the Company and its banking subsidiary are subject to the regulations of certain federal and state agencies and undergo periodic examinations by those regulatory agencies. The Company has one operating segment.
Use of Estimates	The consolidated financial statements of the Company have been prepared in conformity with U.S. generally accepted accounting principles (“U.S. GAAP”). In preparing the consolidated financial statements, management is required to make estimates and assumptions, which significantly affect the reported amounts in the consolidated financial statements. Such estimates include the valuation of loans, goodwill, intangible assets, indemnification assets, and other long-lived assets, along with assumptions used in the calculation of income taxes, among others. These estimates and assumptions are based on management's best estimates and judgment. Management evaluates its estimates and assumptions on an ongoing basis using experience and other factors, including the current economic environment, which management believes to be reasonable under the circumstances. Management adjusts such estimates and assumptions when facts and circumstances dictate. Decreased real estate values, volatile credit markets, and unemployment have combined to increase the uncertainty inherent in such estimates and assumptions. As future events and their effects cannot be determined with precision, actual results could differ significantly from these estimates. Changes in those estimates resulting from continuing changes in the economic environment will be reflected in the financial statements in future periods.
Cash Flow Information	For purposes of reporting cash flows, the Company considers cash and due from banks, interest-bearing deposits and federal funds sold that mature within 90 days of the balance sheet date to be cash and cash equivalents. At December 31, 2017 and 2016 , approximately $17.5 million , and $18.2 million , respectively, of cash and due from banks represented required reserves on deposits maintained by the Company in accordance with Federal Reserve Bank requirements.
Investments	The Company has classified all investments in debt securities as available for sale or held to maturity. Securities classified as available for sale are carried at fair value. Unrealized holding gains and losses for available for sale securities are excluded from earnings and reported as a net amount in a separate component of shareholders' equity until realized. All previous fair value adjustments included in the separate component of shareholders' equity are reversed upon sale. Securities classified as held to maturity are carried at historical cost and adjusted for amortization of premiums and accretion of discounts. Declines in the fair value of securities below their cost deemed to be other-than-temporary are reflected in operations as realized losses. In estimating other-than-temporary impairment losses, management systematically evaluates investment securities for other-than-temporary declines in fair value on a quarterly basis. This analysis requires management to consider various factors, which include (1) the present value of the cash flows expected to be collected compared to the amortized cost of the security, (2) duration and magnitude of the decline in value, (3) the financial condition of the issuer or issuers, (4) structure of the security, and (5) the intent to sell the security or whether it's more likely than not the Company would be required to sell the security before its anticipated recovery in market value. Premiums and discounts are amortized or accreted over the expected lives of the respective securities as an adjustment to yield using the interest method. Dividend and interest income is recognized when earned. Realized gains and losses are included in earnings and are derived using the specific identification method for determining the cost of securities sold.
Loans Receivable	The Company provides long-term financing of one-to-four-family residential real estate by originating fixed and variable rate loans. Long-term fixed and variable rate loans are sold into the secondary market with limited recourse. Upon receipt of an application for a real estate loan, the Company determines whether the loan will be sold into the secondary market or retained in the Company's loan portfolio. The interest rates on the loans sold are locked with the buyer and the Company bears no interest rate risk related to these loans. Mortgage loans held for sale are carried at the lower of cost or fair value, which is determined on a specific identification method. The Company does not retain servicing on any loans sold, nor did the Company have any capitalized mortgage servicing rights at December 31, 2017 or 2016 . Gains on the sale of loans held for sale are reported net of direct origination fees and costs in the Company's consolidated statements of operations. Portfolio Loans Loans are reported at the principal balance outstanding, net of unearned fees, costs, and premiums or discounts on acquired loans. Loan origination fees, direct origination costs, and premiums or discounts resulting from acquired loans are deferred and recognized over the lives of the related loans as a yield adjustment using the interest method. Interest income on loans is accrued to income based on the principal amount outstanding. The recognition of interest income is discontinued when a loan becomes 90 days past due or a significant deterioration in the borrower's credit has occurred which, in management's judgment, negatively impacts the collectibility of the loan. Unpaid interest on such loans is reversed at the time the loan becomes uncollectible and subsequent interest payments received are applied to principal if any doubt exists as to the collectibility of such principal; otherwise, such receipts are recorded as interest income. Loans that have not been restructured are returned to accrual status when management believes full collectibility of principal and interest is expected. Non-accrual loans that have been restructured will remain in a non-accrual status until the borrower has made at least six months of consecutive contractual payments. Purchased Credit Impaired ("PCI") Loans PCI loans were acquired in a business combination or transaction, that have evidence of deterioration of credit quality since origination and for which it is probable, at acquisition, that the Company will be unable to collect all contractually required payments receivable. PCI loans were initially recorded at fair value (as determined by the present value of expected future cash flows) with no valuation allowance. The difference between the undiscounted cash flows expected at acquisition and the investment in the loans, or the “accretable yield,” is recognized as interest income on a level-yield method over the life of the loans. Contractually required payments for interest and principal that exceed the undiscounted cash flows expected at acquisition, or the “nonaccretable difference,” are not recognized as a yield adjustment or as a loss accrual or a valuation allowance. The Company aggregates individual loans with common risk characteristics into pools of loans. Increases in expected cash flows subsequent to the initial investment are recognized prospectively through adjustment of the yield on the loans over their remaining lives. Decreases in expected cash flows due to an inability to collect contractual cash flows are recognized as impairment through the provision for loan losses account. Any allowance for loan loss on these pools reflect only losses incurred after the acquisition. Disposals of loans, including sales of loans, paydowns, payments in full or foreclosures result in the removal or reduction of the loan from the loan pool. PCI loans are generally considered accruing and performing, as the loans accrete income over the estimated life of the loan, in circumstances where cash flows are reasonably estimable by management. Accordingly, PCI loans that could be contractually past due could be considered to be accruing and performing. If the timing and amount of future cash flows is not reasonably estimable or is less than the carrying value, the loans may be classified as nonaccrual loans and the purchase price discount on those loans is not recorded as interest income until the timing and amount of future cash flows can be reasonably estimable. Impaired Loans Loans are considered “impaired” when it becomes probable that the Company will be unable to collect all amounts due according to the loan's contractual terms. Non-accrual loans, loans past due greater than 90 days and still accruing, unless adequately secured and in the process of collection, and restructured loans qualify as “impaired loans.” Restructured loans involve the granting of a concession to a borrower experiencing financial difficulty involving the modification of terms of the loan, such as changes in payment schedule or interest rate. When measuring impairment, the expected future cash flows of an impaired loan are discounted at the loan's effective interest rate at origination. Alternatively, impairment can be measured by reference to an observable market price, if one exists, or the fair value of the collateral for a collateral-dependent loan. Interest income on impaired loans is not accrued but is recorded when cash is received and only if principal is considered to be fully collectible. Loans and leases, which are deemed uncollectible, are charged off to the allowance for loan losses, while recoveries of amounts previously charged off are credited to the allowance for loan losses. Impaired loans exclude PCI loans, as described above. Although, if the timing and amount of future cash flows is not reasonably estimable, the loans may be classified as nonaccrual loans and the purchase price discount on those loans is not recorded as interest income until the timing and amount of future cash flows can be reasonably estimated. See Note 5 – Loans for more information on these loans. Loans are generally placed on non-accrual status when contractually past due 90 days or more as to interest or principal payments. Additionally, whenever management becomes aware of facts or circumstances that may adversely impact the collectability of principal or interest on loans, it is management's practice to place such loans on non-accrual status immediately, rather than delaying such action until the loans become 90 days past due. Previously accrued and uncollected interest on such loans is reversed. Income is recorded only to the extent that a determination has been made that the principal balance of the loan is collectable and the interest payments are subsequently received in cash, or for a restructured loan, the borrower has made six consecutive contractual payments. If collectability of the principal is in doubt, payments received are applied to loan principal. Loans past due 90 days or more but still accruing interest are also generally included in nonperforming loans. Loans past due 90 days or more but still accruing are classified as such where the underlying loans are both well secured (the collateral value is sufficient to cover principal and accrued interest) and are in the process of collection. At December 31, 2017 , we did not have any loans past due greater than 90 days and not included in nonperforming loans. Loan Charge-Offs Loans are charged-off when the primary and secondary sources of repayment (cash flow, collateral, guarantors, etc.) are less than their carrying value.
Allowance for Loan Losses	Allowance For Loan Losses The allowance for loan losses is increased by provision charged to expense and is available to absorb charge-offs, net of recoveries. Management utilizes a systematic, documented approach in determining the appropriate level of the allowance for loan losses. The level of the allowance reflects management's continuing evaluation of industry concentrations; specific credit risks; loan loss experience; current loan portfolio quality; present economic, political and regulatory conditions; and probable losses inherent in the current loan portfolio. The determination of the appropriate level of the allowance for loan losses inherently involves a degree of subjectivity and requires that the Company make significant estimates of current credit risks and future trends, all of which may undergo material changes. Changes in economic conditions affecting borrowers, new information regarding existing loans, identification of additional problem loans and other factors, both within and outside of our control, may require an increase in the allowance for loan losses. Management believes the allowance for loan losses is adequate to absorb inherent losses in the loan portfolio. While management uses available information to recognize losses on loans, future additions to the allowance may be necessary based on changes in economic conditions and other factors. In addition, various regulatory agencies, as an integral part of the examination process, periodically review the Bank's loan portfolio. Such agencies may require additions to the allowance for loan losses based on their judgments and interpretations of information available to them at the time of their examinations. Allowance for Loan Losses on PCI Loans The Company updates its cash flow projections for PCI loans on a periodic basis. Assumptions utilized in this process include projections related to probability of default, loss severity, prepayment, extensions and recovery lag. Projections related to probability of default and prepayment are calculated utilizing a loan migration analysis and management's assessment of loss exposure including the fair value of underlying collateral. The loan migration analysis is a matrix that specifies the probability of a loan pool transitioning into a particular delinquency or liquidation state given its current performance at the measurement date. Loss severity factors are based upon industry data and historical experience. Any decreases in expected cash flows after the acquisition date and subsequent measurement periods are recognized by recording an impairment in allowance for loan losses.
Other Real Estate	Other real estate represents property acquired through foreclosure or deeded to the Company in lieu of foreclosure on loans on which the borrowers have defaulted on the payment of principal or interest. Other real estate is recorded on an individual asset basis at the lower of cost or fair value less estimated costs to sell. The fair value of other real estate is based upon estimates of future cash flows, market value of similar assets, if available, or independent appraisals. These estimates involve significant uncertainties and judgments. As a result, fair value estimates may not be realizable in a current sale or settlement of the other real estate. Subsequent reductions in fair value are expensed within noninterest expense. Gains and losses resulting from the sale of other real estate are credited or charged to current period earnings. Costs of maintaining and operating other real estate are expensed as incurred, and expenditures to complete or improve other real estate properties are capitalized if the expenditures are expected to be recovered upon ultimate sale of the property.
Fixed Assets	Buildings, leasehold improvements, furniture, fixtures, equipment, and capitalized software are stated at cost less accumulated depreciation. All categories are computed using the straight-line method over their respective estimated useful lives. Furniture, fixtures and equipment is depreciated over three to ten years, buildings and leasehold improvements over ten to forty years, and capitalized software over three years based upon estimated lives or lease obligation periods.
State Tax Credits Held for Sale	The Company has purchased the rights to receive 10 -year streams of state tax credits at agreed upon discount rates and sells such tax credits to its clients and others. All state tax credits purchased prior to 2009 are accounted for at fair value. All state tax credits purchased since 2009 are accounted for at cost. The Company elected not to account for the state tax credits purchased since 2009 at fair value in order to limit the volatility of the fair value changes in the Company's consolidated statements of operations.
Cash Surrender Value of Life Insurance	The Company has purchased bank-owned life insurance policies on certain bank officers. Bank-owned life insurance is recorded at its cash surrender value. Changes in the cash surrender values are included in noninterest income.
Federal Home Loan Bank Stock	The Bank, as a member of the Federal Home Loan Bank of Des Moines (“FHLB”), is required to maintain an investment in the capital stock of the FHLB. The stock is redeemable at par by the FHLB, and is, therefore, carried at cost and periodically evaluated for impairment. The Company records FHLB dividends in interest income.
Goodwill and Other Intangible Assets	The Company tests goodwill for impairment on an annual basis and whenever events or changes in circumstances indicate that the Company may not be able to recover the respective asset's carrying amount. The Company's annual test for impairment was performed in the fourth quarter of December 31, 2017 . Such tests involve the use of estimates and assumptions. Core deposit intangibles are amortized using an accelerated method over an estimated useful life of approximately 10 years. Potential impairments to goodwill must first be identified by performing a qualitative assessment which evaluates relevant events or circumstances to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount. If this test indicates it is more likely than not that goodwill has been impaired, then a quantitative impairment test is completed. The quantitative impairment test calculates the fair value of the reporting unit and compares it with its carrying amount, including goodwill. If the carrying amount of goodwill exceeds its implied fair market value, an impairment loss is recognized. That loss is equal to the carrying amount of goodwill that is in excess of its implied fair market value.
Impairment of Long-Lived Assets	Long-lived assets, such as fixed assets and purchased intangibles subject to amortization, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to estimated undiscounted future cash flows expected to be generated by the asset. If the carrying amount of an asset exceeds its estimated future cash flows, an impairment charge is recognized in the amount by which the carrying amount of the asset exceeds the fair value of the asset. Assets to be disposed of are separately presented in the balance sheet and reported at the lower of the carrying amount or fair value less costs to sell, and are no longer depreciated. The assets and liabilities of a disposal group classified as held for sale are presented separately in the appropriate asset and liability sections of the balance sheet.
Derivative Financial Instruments and Hedging Activities	The Company uses derivative financial instruments to assist in the management of interest rate sensitivity and to modify the repricing, maturity and option characteristics of certain assets and liabilities. In addition, the Company also offers an interest rate hedge program that includes interest rate swaps to assist its customers in managing their interest rate risk profile. In order to eliminate the interest rate risk associated with offering these products, the Company enters into derivative contracts with third parties to offset the customer contracts. Derivative instruments are required to be measured at fair value and recognized as either assets or liabilities in the consolidated financial statements. Fair value represents the payment the Company would receive or pay if the item were sold or bought in a current transaction. The accounting for changes in fair value (gains or losses) of a hedged item is dependent on whether the related derivative is designated and qualifies for “hedge accounting.” The Company assigns derivatives to one of these categories at the purchase date: cash flow hedge, fair value hedge, or non-designated derivatives. An assessment of the expected and ongoing hedge effectiveness of any derivative designated a fair value hedge or cash flow hedge is performed as required by the accounting standards. Derivatives are included in other assets and other liabilities in the consolidated balance sheets. Generally, the only derivative instruments used by the Company have been interest rate swaps and interest rate caps. The Company does not currently have derivative instruments designated as fair value or cash flow hedges. Certain derivative financial instruments are not designated as cash flow or as fair value hedges for accounting purposes. These non-designated derivatives are intended to provide interest rate protection on net interest income or noninterest income but do not meet hedge accounting treatment. Customer accommodation interest rate swap contracts are not designated as hedging instruments. Changes in the fair value of these instruments are recorded in interest income or noninterest income in the consolidated statements of income depending on the underlying hedged item.
Income Taxes	The Company and its subsidiaries file a consolidated federal income tax return. Deferred tax assets and liabilities are recognized for the estimated future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates in effect for the year in which those temporary differences are expected to be recovered or settled. We evaluated the need for deferred tax asset valuation allowances based on a more-likely-than-not standard. The ability to realize deferred tax assets depends on the ability to generate sufficient positive taxable income within the carryback or carryforward periods provided for in the laws for each applicable taxing jurisdiction. We consider the following possible sources of taxable income: future reversal patterns of existing taxable temporary differences, future taxable income exclusive of reversing temporary differences, taxable income in prior carryback years and the availability of qualified tax planning strategies. The assessment regarding whether a valuation allowance is required or should be adjusted depends on all available positive and negative factors including, but not limited to, nature, frequency, and severity of recent losses, duration of available carryforward periods, experience with tax attributes expiring unused and near and medium term financial outlook. Because of the complexity of tax laws and regulations, interpretation can be difficult and subject to legal judgment given specific facts and circumstances. It is possible that others, given the same information, may at any point in time reach different reasonable conclusions regarding the estimated amounts of accrued taxes. The SEC staff issued SAB 118, which provides guidance on accounting for the tax effects of the Tax Cuts and Jobs Act of 2017 (“Tax Act”). SAB 118 provides a measurement period that should not extend beyond one year from the Tax Act enactment date for companies to complete the accounting under ASC 740. In accordance with SAB 118, a company must reflect the income tax effects of those aspects of the Act for which the accounting under ASC 740 is complete. To the extent that a company’s accounting for certain income tax effects of the Tax Act is incomplete but it is able to determine a reasonable estimate, it must record a provisional estimate in the financial statements. If a company cannot determine a provisional estimate to be included in the financial statements, it should continue to apply ASC 740 on the basis of the provisions of the tax laws that were in effect immediately before the enactment of the Tax Act. The Company has recorded amounts based on the information known and reasonable estimates used as of December 31, 2017, but are subject to change based on a number of factors. The Company will complete its analysis of certain tax positions at the time it files its tax returns for the year ended December 31, 2017 and will be able to conclude if any further adjustments to the provisional estimate of the impact recorded is required.
Stock-Based Compensation	Stock-based compensation is recognized as an expense for stock options, restricted stock awards, and restricted stock units granted to employees in return for employee service. Equity classified awards are measured at the grant date fair value using either an observable market value or a valuation methodology, and recognized over the requisite service period on a straight-line basis. Forfeitures are recorded as they occur. A description of the Company's stock-based employee compensation plan is described in Note 15 - Compensation Plans.
Acquisitions and Divestitures	Acquisitions and business combinations are accounted for using the acquisition method of accounting. The assets and liabilities of the acquired entities have been recorded at their estimated fair values at the date of acquisition. Goodwill represents the excess of the purchase price over the fair value of net assets acquired, including the amount assigned to identifiable intangible assets. The purchase price allocation process requires an estimation of the fair values of the assets acquired and the liabilities assumed. When a business combination agreement provides for an adjustment to the cost of the combination contingent on future events, the Company includes an estimate of the acquisition-date fair value as part of the cost of the combination. To determine the fair values, the Company relies on third party valuations, such as appraisals, or internal valuations based on discounted cash flow analyses or other valuation techniques. The results of operations of the acquired business are included in the Company's consolidated financial statements from the date of acquisition. Merger-related costs are costs the Company incurs to effect a business combination. In 2017, the Company changed its presentation of Merger related expenses as a separate component of Noninterest expenses on the Condensed Consolidated Statements of Operations. Merger related expenses include costs directly related to merger or acquisition activity and include legal and professional fees, system consolidation and conversion costs, and compensation costs such as severance and retention incentives for employees impacted by acquisition activity. The Company accounts for merger-related costs as expenses in the periods in which the costs are incurred and the services are received. For divestitures, the Company measures an asset (disposal group) classified as held for sale at the lower of its carrying value at the date the asset is initially classified as held for sale or its fair value less costs to sell. The Company reports the results of operations of an entity or group of components that either has been disposed of or held for sale as discontinued operations only if the disposal of that component represents a strategic shift that has or will have a major effect on an entity's operations and financial results. Any incremental direct costs incurred to transact the sale are allocated against the gain or loss on the sale. These costs would include items like legal fees, title transfer fees, broker fees, etc. Any goodwill and intangible assets associated with the portion of the reporting unit to be disposed of is included in the carrying amount of the business in determining the gain or loss on the sale.
Basic and Diluted Earnings Per Common Share	Basic earnings per common share data is calculated by dividing net income available to common shareholders by the weighted average number of common shares outstanding during the period. Common shares outstanding include common stock and restricted stock awards where recipients have satisfied the vesting terms. Diluted earnings per common share gives effect to all dilutive potential common shares outstanding during the period using the treasury stock method.
Consolidated Statement of Comprehensive Income	The Consolidated Statement of Comprehensive Income includes the amount and the related tax impact that have been reclassified from accumulated other comprehensive income to net income. The classification adjustment for unrealized loss/gain on sale of securities included in net income has been recorded through the gain on sale of investment securities line item, within noninterest income, in the Company's Consolidated Statements of Operations.
Available-for-sale Securities	The unrealized losses at both December 31, 2017 , and 2016 , were primarily attributable to changes in market interest rates since the securities were purchased. Management systematically evaluates investment securities for other-than-temporary declines in fair value on a quarterly basis. This analysis requires management to consider various factors, which include among other considerations (1) the present value of the cash flows expected to be collected compared to the amortized cost of the security, (2) duration and magnitude of the decline in value, (3) the financial condition of the issuer or issuers, (4) structure of the security, and (5) the intent to sell the security or whether it is more likely than not that the Company would be required to sell the security before its anticipated recovery in market value. At December 31, 2017 and 2016 , management performed its quarterly analysis of all securities with an unrealized loss and concluded no individual securities were other-than-temporarily impaired.
Reclassification, Policy [Policy Text Block]	Some items in the prior year financial statements were reclassified to conform to the current presentation. In 2017, the Company changed its presentation of loans on the face of the Consolidated Balance Sheets to combine originated loans with purchased loans. See Note 5 - Loans for more information. The Company also changed its presentation of the Noninterest Income section on the face of the Consolidated Statements of Operations to separate card services revenue from other service charges and fee income. The difference was reclassified into miscellaneous income. Merger related expenses were reclassified from other expenses to be a separate component of the Noninterest Expense section on the Consolidated Statements of Operations. Reclassifications had no effect on prior year net income or shareholders' equity.

Acquisitions & Divestitures Acq

Acquisitions & Divestitures Acquisitions & Divestitures (Tables)	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block]	The following table presents the assets acquired and liabilities assumed of JCB as of February 10, 2017, and their estimated fair values: (in thousands) As Recorded by JCB Adjustments As Recorded by EFSC Assets acquired: Cash and cash equivalents $ 33,739 $ — $ 33,739 Interest-bearing deposits 1,715 — 1,715 Securities 148,670 — 148,670 Portfolio loans, net 685,905 (11,094 ) (a) 674,811 Other real estate owned 6,762 (5,082 ) (b) 1,680 Other investments 2,695 — 2,695 Fixed assets, net 21,780 (3,325 ) (c) 18,455 Accrued interest receivable 2,794 — 2,794 Goodwill 7,806 (7,806 ) (d) — Other intangible assets 25 11,489 (e) 11,514 Deferred tax assets 4,634 3,991 (f) 8,625 Other assets 19,107 (296 ) (g) 18,811 Total assets acquired $ 935,632 $ (12,123 ) $ 923,509 Liabilities assumed: Deposits $ 764,539 $ 629 (h) $ 765,168 Other borrowings 55,430 681 (i) 56,111 Trust preferred securities 12,887 (382 ) (j) 12,505 Accrued interest payable 653 — 653 Other liabilities 5,006 65 5,071 Total liabilities assumed $ 838,515 $ 993 $ 839,508 Net assets acquired $ 97,117 $ (13,116 ) $ 84,001 Consideration paid: Cash $ 29,283 Common stock 141,729 Total consideration paid $ 171,012 Goodwill $ 87,011 (a) Fair value adjustments based on the Company’s evaluation of the acquired loan portfolio, write-off of net deferred loan costs, reclassification from other real estate owned, and elimination of the allowance for loan losses recorded by JCB. The fair value discount recorded to the loan portfolio is $24.7 million , inclusive of the allowance for loan losses previously recorded by JCB. (b) Fair value adjustment based on the Company’s evaluation of the acquired other real estate portfolio, and reclassification to portfolio loans. (c) Fair value adjustments based on the Company’s evaluation of the acquired premises and equipment. (d) Eliminate JCB’s recorded goodwill. (e) Record the core deposit intangible asset on the acquired core deposit accounts. Amount to be amortized using a sum of years digits method over a 10 year useful life. (f) Adjustment for deferred taxes at the acquisition date. (g) Fair value adjustment based on evaluation of other assets. (h) Fair value adjustment to time deposits based on current interest rates. (i) Fair value adjustment to the FHLB advances based on current interest rates. (j) Fair value adjustment based on the Company's evaluation of the trust preferred securities.
Business Acquisition, Pro Forma Information [Table Text Block]	The following table provides the unaudited pro forma information for the results of operations for the twelve months ended December 31, 2017 and 2016, as if the acquisition had occurred on January 1, 2016. The pro forma results combine the historical results of JCB with the Company’s Consolidated Statements of Income, adjusted for the impact of the application of the acquisition method of accounting including loan discount accretion, intangible assets amortization, and deposit and trust preferred securities premium accretion, net of taxes. The pro forma results have been prepared for comparative purposes only and are not necessarily indicative of the results that would have been obtained had the acquisition actually occurred on January 1, 2016. No assumptions have been applied to the pro forma results of operations regarding possible revenue enhancements, expense efficiencies or asset dispositions. Only the acquisition related expenses that have been incurred as of December 31, 2017 are included in net income in the table below. Pro Forma Twelve months ended December 31, (in thousands, except per share data) 2017 2016 Total revenues (net interest income plus noninterest income) $ 213,910 $ 199,033 Net income 47,227 56,994 Diluted earnings per common share 2.03 2.42

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Summary of Per Common Share Data and Amounts	The following table presents a summary of per common share data and amounts for the periods indicated. Years ended December 31, (in thousands, except per share data) 2017 2016 2015 Net income as reported $ 48,190 $ 48,837 $ 38,450 Weighted average common shares outstanding 22,953 20,003 19,984 Additional dilutive common stock equivalents 296 287 333 Weighted average diluted common shares outstanding 23,249 20,290 20,317 Basic earnings per common share: $ 2.10 $ 2.44 $ 1.92 Diluted earnings per common share: $ 2.07 $ 2.41 $ 1.89

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Schedule of Available-for-sale and Held-to-Maturity Securities Reconciliation	The following table presents the amortized cost, gross unrealized gains and losses and fair value of securities available for sale and held to maturity: December 31, 2017 (in thousands) Amortized Cost Gross Gross Fair Value Available for sale securities: Obligations of U.S. Government-sponsored enterprises $ 99,878 $ 6 $ (660 ) $ 99,224 Obligations of states and political subdivisions 34,181 674 (213 ) 34,642 Agency mortgage-backed securities 513,082 727 (6,293 ) 507,516 Total securities available for sale $ 647,141 $ 1,407 $ (7,166 ) $ 641,382 Held to maturity securities: Obligations of states and political subdivisions $ 14,031 $ 69 $ (46 ) $ 14,054 Agency mortgage-backed securities 59,718 16 (330 ) 59,404 Total securities held to maturity $ 73,749 $ 85 $ (376 ) $ 73,458 December 31, 2016 (in thousands) Amortized Cost Gross Gross Fair Value Available for sale securities: Obligations of U.S. Government-sponsored enterprises $ 107,312 $ 348 $ — $ 107,660 Obligations of states and political subdivisions 36,486 630 (485 ) 36,631 Agency mortgage-backed securities 319,345 1,101 (3,940 ) 316,506 Total securities available for sale $ 463,143 $ 2,079 $ (4,425 ) $ 460,797 Held to maturity securities: Obligations of states and political subdivisions $ 14,759 $ 11 $ (242 ) $ 14,528 Agency mortgage-backed securities 65,704 45 (638 ) 65,111 Total securities held to maturity $ 80,463 $ 56 $ (880 ) $ 79,639 At December 31, 2017 , and 2016 , there were no holdings of securities of any one issuer in an amount greater than 10% of shareholders’ equity, other than the U.S. Government agencies and sponsored enterprises. The agency mortgage-backed securities are all issued by U.S. Government-sponsored enterprises. Securities having a fair value of $500.0 million and $407.3 million at December 31, 2017 , and December 31, 2016 , respectively, were pledged as collateral to secure deposits of public institutions and for other purposes as required by law or contract provisions.
Schedule of Available-for-sale and Held-to-Maturity Securities Reconciliation	The following table presents the amortized cost, gross unrealized gains and losses and fair value of securities available for sale and held to maturity: December 31, 2017 (in thousands) Amortized Cost Gross Gross Fair Value Available for sale securities: Obligations of U.S. Government-sponsored enterprises $ 99,878 $ 6 $ (660 ) $ 99,224 Obligations of states and political subdivisions 34,181 674 (213 ) 34,642 Agency mortgage-backed securities 513,082 727 (6,293 ) 507,516 Total securities available for sale $ 647,141 $ 1,407 $ (7,166 ) $ 641,382 Held to maturity securities: Obligations of states and political subdivisions $ 14,031 $ 69 $ (46 ) $ 14,054 Agency mortgage-backed securities 59,718 16 (330 ) 59,404 Total securities held to maturity $ 73,749 $ 85 $ (376 ) $ 73,458 December 31, 2016 (in thousands) Amortized Cost Gross Gross Fair Value Available for sale securities: Obligations of U.S. Government-sponsored enterprises $ 107,312 $ 348 $ — $ 107,660 Obligations of states and political subdivisions 36,486 630 (485 ) 36,631 Agency mortgage-backed securities 319,345 1,101 (3,940 ) 316,506 Total securities available for sale $ 463,143 $ 2,079 $ (4,425 ) $ 460,797 Held to maturity securities: Obligations of states and political subdivisions $ 14,759 $ 11 $ (242 ) $ 14,528 Agency mortgage-backed securities 65,704 45 (638 ) 65,111 Total securities held to maturity $ 80,463 $ 56 $ (880 ) $ 79,639 At December 31, 2017 , and 2016 , there were no holdings of securities of any one issuer in an amount greater than 10% of shareholders’ equity, other than the U.S. Government agencies and sponsored enterprises. The agency mortgage-backed securities are all issued by U.S. Government-sponsored enterprises. Securities having a fair value of $500.0 million and $407.3 million at December 31, 2017 , and December 31, 2016 , respectively, were pledged as collateral to secure deposits of public institutions and for other purposes as required by law or contract provisions.
Investments Classified by Contractual Maturity Date	The amortized cost and estimated fair value of debt securities at December 31, 2017 , by contractual maturity, are shown below. Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. The weighted average life of the agency mortgage-backed securities is approximately 4 years. Available for sale Held to maturity (in thousands) Amortized Cost Estimated Fair Value Amortized Cost Estimated Due in one year or less $ 3,060 $ 3,076 $ — $ — Due after one year through five years 110,910 110,480 186 195 Due after five years through ten years 14,573 14,980 12,977 12,981 Due after ten years 5,516 5,330 868 878 Agency mortgage-backed securities 513,082 507,516 59,718 59,404 $ 647,141 $ 641,382 $ 73,749 $ 73,458
Schedule of Unrealized Loss on Investments	The following table represents a summary of investment securities that had an unrealized loss: December 31, 2017 Less than 12 months 12 months or more Total (in thousands) Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Obligations of U.S. Government-sponsored enterprises $ 89,309 $ 660 $ — $ — $ 89,309 $ 660 Obligations of states and political subdivisions 13,951 259 — — 13,951 259 Agency mortgage-backed securities 469,655 6,034 12,229 589 481,884 6,623 $ 572,915 $ 6,953 $ 12,229 $ 589 $ 585,144 $ 7,542 December 31, 2016 Less than 12 months 12 months or more Total (in thousands) Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Obligations of states and political subdivisions $ 21,361 $ 408 $ 3,553 $ 320 $ 24,914 $ 728 Agency mortgage-backed securities 267,734 4,084 12,883 493 280,617 4,577 $ 289,095 $ 4,492 $ 16,436 $ 813 $ 305,531 $ 5,305
Schedule of Realized Gain (Loss)	The gross gains and losses realized from sales of available for sale investment securities were as follows: December 31, (in thousands) 2017 2016 2015 Gross gains realized $ 22 $ 86 $ 63 Gross losses realized — — (40 ) Proceeds from sales 144,076 2,493 41,069

Portfolio Loans (Tables)

Portfolio Loans (Tables)	12 Months Ended
	Dec. 31, 2017
Non-covered Loans [Line Items]
Summary of Loans to Executive Officers and Directors	Following is a summary of activity for the years ended December 31, 2017 , 2016 , and 2015 of loans to executive officers and directors, or to entities in which such individuals had beneficial interests as a shareholder, officer, or director. Such loans were made in the normal course of business on substantially the same terms, including interest rates and collateral, as those prevailing at the time for comparable transactions with other customers and did not involve more than the normal risk of collectibility. (in thousands) December 31, 2017 December 31, 2016 December 31, 2015 Balance at beginning of year $ 15,406 $ 4,394 $ 13,513 New loans and advances 1,353 11,539 641 Payments and other reductions (11,410 ) (527 ) (9,760 ) Balance at end of year $ 5,349 $ 15,406 $ 4,394
Non-Covered Loans
Non-covered Loans [Line Items]
Summary of Portfolio Loans by Category	The table below shows the loan portfolio composition including carrying value by segment of loans accounted for at amortized cost, which includes our originated loans, and loans accounted for as PCI. (in thousands) December 31, 2017 December 31, 2016 Loans accounted for at amortized cost $ 4,022,896 $ 3,118,392 Loans accounted for as PCI 74,154 39,769 Total loans $ 4,097,050 $ 3,158,161 The following tables refer to loans not accounted for as PCI loans. Below is a summary of loans by category at December 31, 2017 and 2016 : (in thousands) December 31, 2017 December 31, 2016 Commercial and industrial $ 1,918,720 $ 1,632,714 Real estate loans: Commercial - investor owned 769,275 544,808 Commercial - owner occupied 554,589 350,148 Construction and land development 303,091 194,542 Residential 341,312 240,760 Total real estate loans 1,968,267 1,330,258 Consumer and other 137,234 156,182 Loans, before unearned loan (fees) costs 4,024,221 3,119,154 Unearned loan (fees) costs, net (1,325 ) (762 ) Loans, including unearned loan fees $ 4,022,896 $ 3,118,392
Summary of Allowance for Loan Losses and the Recorded Investment in Portfolio Loans by Class and Category Based on Impairment Method	A summary of activity in the allowance for loan losses and the recorded investment in loans by class and category based on impairment method for the years ended indicated below is as follows: (in thousands) Commercial and industrial CRE - investor owned CRE - owner occupied Construction and land development Residential real estate Consumer and other Total Balance at December 31, 2017 Allowance for loan losses: Balance, beginning of year $ 26,996 $ 3,420 $ 2,890 $ 1,304 $ 2,023 $ 932 $ 37,565 Provision (provision reversal) 8,737 456 404 336 797 34 10,764 Losses charged off (9,872 ) (117 ) (90 ) (254 ) (973 ) (201 ) (11,507 ) Recoveries 545 131 104 101 390 73 1,344 Balance, end of year $ 26,406 $ 3,890 $ 3,308 $ 1,487 $ 2,237 $ 838 $ 38,166 Balance at December 31, 2016 Allowance for loan losses: Balance, beginning of year $ 22,056 $ 3,484 $ 2,969 $ 1,704 $ 1,796 $ 1,432 $ 33,441 Provision (provision reversal) 6,569 (11 ) (1,202 ) (1,334 ) 129 1,400 5,551 Losses charged off (2,303 ) (95 ) — — (25 ) (1,912 ) (4,335 ) Recoveries 674 42 1,123 934 123 12 2,908 Balance, end of year $ 26,996 $ 3,420 $ 2,890 $ 1,304 $ 2,023 $ 932 $ 37,565 Balance at December 31, 2015 Allowance for loan losses: Balance, beginning of year $ 16,983 $ 4,382 $ 3,135 $ 1,715 $ 2,830 $ 1,140 $ 30,185 Provision (provision reversal) 6,976 (303 ) (1,626 ) (335 ) (58 ) 218 4,872 Losses charged off (3,699 ) (664 ) (38 ) (350 ) (1,313 ) (27 ) (6,091 ) Recoveries 1,796 69 1,498 674 337 101 4,475 Balance, end of year $ 22,056 $ 3,484 $ 2,969 $ 1,704 $ 1,796 $ 1,432 $ 33,441 (in thousands) Commercial and industrial CRE - investor owned CRE - owner occupied Construction and land development Residential real estate Consumer and other Total Balance December 31, 2017 Allowance for loan losses - Ending balance: Individually evaluated for impairment $ 2,508 $ — $ 71 $ — $ — $ — $ 2,579 Collectively evaluated for impairment 23,898 3,890 3,237 1,487 2,237 838 35,587 Total $ 26,406 $ 3,890 $ 3,308 $ 1,487 $ 2,237 $ 838 $ 38,166 Loans - Ending balance: Individually evaluated for impairment $ 12,665 $ 422 $ 1,975 $ 136 $ 1,602 $ 375 $ 17,175 Collectively evaluated for impairment 1,906,055 768,853 552,614 302,955 339,710 135,534 4,005,721 Total $ 1,918,720 $ 769,275 $ 554,589 $ 303,091 $ 341,312 $ 135,909 $ 4,022,896 Balance December 31, 2016 Allowance for loan losses - Ending balance: Individually evaluated for impairment $ 2,909 $ — $ — $ 155 $ — $ — $ 3,064 Collectively evaluated for impairment 24,087 3,420 2,890 1,149 2,023 932 34,501 Total $ 26,996 $ 3,420 $ 2,890 $ 1,304 $ 2,023 $ 932 $ 37,565 Loans - Ending balance: Individually evaluated for impairment $ 12,523 $ 430 $ 1,854 $ 1,903 $ 62 $ — $ 16,772 Collectively evaluated for impairment 1,620,191 544,378 348,294 192,639 240,698 155,420 3,101,620 Total $ 1,632,714 $ 544,808 $ 350,148 $ 194,542 $ 240,760 $ 155,420 $ 3,118,392
Summary of Portfolio Loans Individually Evaluated for Impairment and Recorded Investment in Impaired Non-Covered Loans by Category	A summary of nonperforming loans individually evaluated for impairment by category at December 31, 2017 and 2016 , and the income recognized on impaired loans is as follows: December 31, 2017 (in thousands) Unpaid Recorded Recorded Allowance Total Related Allowance Average Commercial and industrial $ 20,750 $ 2,321 $ 10,344 $ 12,665 $ 2,508 $ 16,270 Real estate: Commercial - investor owned 560 422 — 422 — 521 Commercial - owner occupied 487 — 487 487 71 490 Construction and land development 441 136 — 136 — 331 Residential 1,730 1,602 — 1,602 — 1,735 Consumer and other 375 375 — 375 — 375 Total $ 24,343 $ 4,856 $ 10,831 $ 15,687 $ 2,579 $ 19,722 December 31, 2016 (in thousands) Unpaid Recorded Recorded Allowance Total Related Allowance Average Commercial and industrial $ 12,341 $ 566 $ 11,791 $ 12,357 $ 2,909 $ 4,489 Real estate: Commercial - investor owned 525 435 — 435 — 668 Commercial - owner occupied 225 231 — 231 — 227 Construction and land development 1,904 1,947 359 2,306 155 1,918 Residential 62 62 — 62 — 64 Consumer and other — — — — — — Total $ 15,057 $ 3,241 $ 12,150 $ 15,391 $ 3,064 $ 7,366 December 31, (in thousands) 2017 2016 2015 Total interest income that would have been recognized under original terms on impaired loans $ 1,324 $ 1,079 $ 1,038 Total cash received and recognized as interest income on impaired loans 643 251 226 Total interest income recognized on impaired loans still accruing 63 155 36 There were no loans over 90 days past due and still accruing interest at December 31, 2017 or 2016 .
Schedule of Recorded Investment in Impaired Portfolio Loans by Category	The recorded investment in nonperforming loans by category at December 31, 2017 and 2016 , is as follows: December 31, 2017 (in thousands) Non-accrual Restructured, not on non-accrual Total Commercial and industrial $ 11,946 $ 719 $ 12,665 Real estate: Commercial - investor owned 422 — 422 Commercial - owner occupied 487 — 487 Construction and land development 136 — 136 Residential 1,602 — 1,602 Consumer and other 375 — 375 Total $ 14,968 $ 719 $ 15,687 December 31, 2016 (in thousands) Non-accrual Restructured, not on non-accrual Total Commercial and industrial $ 10,046 $ 2,311 $ 12,357 Real estate: Commercial - investor owned 435 — 435 Commercial - owner occupied 231 — 231 Construction and land development 2,286 20 2,306 Residential 62 — 62 Consumer and other — — — Total $ 13,060 $ 2,331 $ 15,391
Summary of Recorded Investment by for Portfolio Loans Restructured	The recorded investment by category for the portfolio loans that have been restructured during the years ended December 31, 2017 and 2016 , is as follows: Year ended December 31, 2017 Year ended December 31, 2016 (in thousands, except for number of loans) Number of Loans Pre-Modification Outstanding Recorded Balance Post-Modification Outstanding Recorded Balance Number of Loans Pre-Modification Outstanding Recorded Balance Post-Modification Outstanding Recorded Balance Commercial and industrial 1 $ 676 $ 676 4 $ 12,114 $ 12,114 Real estate: Commercial - investor owned — — — 1 248 248 Commercial - owner occupied — — — 1 13 13 Construction and land development — — — 1 20 20 Residential — — — — — — Consumer and other — — — — — — Total 1 $ 676 $ 676 7 $ 12,395 $ 12,395
Summary of Recorded Investment by Category for Portfolio Loans Restructured and Subsequently Defaulted	The restructured portfolio loans primarily resulted from interest rate concessions and changing the terms of the loans. As of December 31, 2017 , the Company allocated no specific reserves to loans that have been restructured. Portfolio loans restructured that subsequently defaulted during the year ended December 31, 2017 , and 2016 , are as follows: Year ended December 31, 2017 Year ended December 31, 2016 (in thousands, except for number of loans) Number of Loans Recorded Balance Number of Loans Recorded Balance Commercial and industrial 2 343 — — Real Estate: Residential 1 5 — — Total 3 348 — —
Summary of Aging of Recorded Investment in Past Due Portfolio Loans by Portfolio Class and Category	The aging of the recorded investment in past due portfolio loans by portfolio class and category at December 31, 2017 and 2016 is shown below: December 31, 2017 (in thousands) 30-89 Days Past Due 90 or More Past Due Total Past Due Current Total Commercial and industrial $ 7,882 $ 1,770 $ 9,652 $ 1,909,068 $ 1,918,720 Real estate: Commercial - investor owned 934 — 934 768,341 769,275 Commercial - owner occupied — — — 554,589 554,589 Construction and land development 76 — 76 303,015 303,091 Residential 1,529 945 2,474 338,838 341,312 Consumer and other 407 — 407 135,502 135,909 Total $ 10,828 $ 2,715 $ 13,543 $ 4,009,353 $ 4,022,896 December 31, 2016 (in thousands) 30-89 Days Past Due 90 or More Past Due Total Past Due Current Total Commercial and industrial $ 334 $ 171 $ 505 $ 1,632,209 $ 1,632,714 Real estate: Commercial - investor owned — 175 175 544,633 544,808 Commercial - owner occupied 212 225 437 349,711 350,148 Construction and land development 355 1,528 1,883 192,659 194,542 Residential 91 — 91 240,669 240,760 Consumer and other 7 — 7 155,413 155,420 Total $ 999 $ 2,099 $ 3,098 $ 3,115,294 $ 3,118,392
Summary of Recorded Investment by Risk Category of Portfolio Loans by Portfolio Class and Category	The Company categorizes loans into risk categories based on relevant information about the ability of borrowers to service their debt, such as current financial information, historical payment experience, credit documentation, and current economic factors among other factors. This analysis is performed on a quarterly basis. The Company uses the following definitions for risk ratings: • Grades 1 , 2 , and 3 – Includes loans to borrowers with a continuous record of strong earnings, sound balance sheet condition and capitalization, ample liquidity with solid cash flow, and whose management team has experience and depth within their industry. • Grade 4 – Includes loans to borrowers with positive trends in profitability, satisfactory capitalization and balance sheet condition, and sufficient liquidity and cash flow. • Grade 5 – Includes loans to borrowers that may display fluctuating trends in sales, profitability, capitalization, liquidity, and cash flow. • Grade 6 – Includes loans to borrowers where an adverse change or perceived weakness has occurred, but may be correctable in the near future. Alternatively, this rating category may also include circumstances where the borrower is starting to reverse a negative trend or condition, or has recently been upgraded from a 7 , 8 , or 9 rating. • Grade 7 – Watch credits are borrowers that have experienced financial setback of a nature that is not determined to be severe or influence ‘ongoing concern’ expectations. Although possible, no loss is anticipated, due to strong collateral and/or guarantor support. • Grade 8 – Substandard credits will include those borrowers characterized by significant losses and sustained downward trends in balance sheet condition, liquidity, and cash flow. Repayment reliance may have shifted to secondary sources. Collateral exposure may exist and additional reserves may be warranted. • Grade 9 – Doubtful credits include borrowers that may show deteriorating trends that are unlikely to be corrected. Collateral values may appear insufficient for full recovery, therefore requiring a partial charge-off, or debt renegotiation with the borrower. The borrower may have declared bankruptcy or bankruptcy is likely in the near term. All doubtful rated credits will be on non-accrual. The recorded investment by risk category of the loans by portfolio class and category at December 31, 2017 and December 31, 2016 is as follows: December 31, 2017 (in thousands) Pass (1-6) Watch (7) Substandard (8) Total Commercial and industrial $ 1,769,102 $ 94,002 $ 55,616 $ 1,918,720 Real estate: Commercial - investor owned 754,010 10,840 4,425 769,275 Commercial - owner occupied 514,616 34,440 5,533 554,589 Construction and land development 292,766 9,983 342 303,091 Residential 329,742 3,648 7,922 341,312 Consumer and other 134,704 10 1,195 135,909 Total $ 3,794,940 $ 152,923 $ 75,033 $ 4,022,896 December 31, 2016 (in thousands) Pass (1-6) Watch (7) Substandard (8) Total Commercial and industrial $ 1,499,114 $ 57,416 $ 76,184 $ 1,632,714 Real estate: Commercial - investor owned 530,494 10,449 3,865 544,808 Commercial - owner occupied 306,658 39,249 4,241 350,148 Construction and land development 185,505 6,575 2,462 194,542 Residential 233,479 2,997 4,284 240,760 Consumer and other 153,984 — 1,436 155,420 Total $ 2,909,234 $ 116,686 $ 92,472 $ 3,118,392

Purchased Credit Impaired ("P37

Purchased Credit Impaired ("PCI") Loans (Tables)	12 Months Ended
	Dec. 31, 2017
Covered Loans [Line Items]
Rollforward of PCI Loans, Net of Allowance for Loan Losses	The following table is a rollforward of PCI loans, net of the allowance for loan losses, for the years ended December 31, 2017 and 2016 . (in thousands) Contractual Cashflows Non-accretable Difference Accretable Yield Carrying Amount Balance January 1, 2017 $ 66,003 $ 18,902 $ 13,176 $ 33,925 Acquisitions 68,763 14,296 5,312 49,155 Principal reductions and interest payments (24,530 ) — — (24,530 ) Accretion of loan discount — — (7,573 ) 7,573 Changes in contractual and expected cash flows due to remeasurement 13,978 (1,465 ) 5,486 9,957 Reductions due to disposals (11,503 ) (2,727 ) (2,439 ) (6,337 ) Balance December 31, 2017 $ 112,711 $ 29,006 $ 13,962 $ 69,743 Balance January 1, 2016 $ 116,689 $ 26,765 $ 25,341 $ 64,583 Principal reductions and interest payments (25,669 ) — — (25,669 ) Accretion of loan discount — — (6,155 ) 6,155 Changes in contractual and expected cash flows due to remeasurement 11,718 766 (1,500 ) 12,452 Reductions due to disposals (36,735 ) (8,629 ) (4,510 ) (23,596 ) Balance December 31, 2016 $ 66,003 $ 18,902 $ 13,176 $ 33,925 The accretable yield is recognized in interest income over the estimated life of the acquired loans using the effective yield method.
Covered Loans
Covered Loans [Line Items]
Summary of PCI Loans by Category	Below is a summary of PCI loans by category at December 31, 2017 and 2016 : December 31, 2017 December 31, 2016 ($ in thousands) Weighted- Average Risk Rating 1 Recorded Investment PCI Loans Weighted- Average Risk Rating 1 Recorded Investment PCI Loans Commercial and industrial 6.38 $ 3,212 5.87 $ 3,523 Real estate loans: Commercial - investor owned 7.36 42,887 6.95 8,162 Commercial - owner occupied 6.48 11,332 6.39 11,863 Construction and land development 5.99 5,883 5.80 4,365 Residential 5.99 10,781 5.64 11,792 Total real estate loans 70,883 36,182 Consumer and other 2.84 59 1.64 64 Purchased credit impaired loans $ 74,154 $ 39,769 (1) Risk ratings are based on the borrower's contractual obligation, which is not reflective of the purchase discount.
Summary of Aging of Recorded Investment in Past Due PCI Loans by Portfolio Class and Category	The aging of the recorded investment in past due PCI loans by portfolio class and category at December 31, 2017 and 2016 is shown below: December 31, 2017 (in thousands) 30-89 Days Past Due 90 or More Past Due Total Past Due Current Total Commercial and industrial $ — $ — $ — $ 3,212 $ 3,212 Real estate: Commercial - investor owned — 3,034 3,034 39,853 42,887 Commercial - owner occupied — 673 673 10,659 11,332 Construction and land development — — — 5,883 5,883 Residential 328 255 583 10,198 10,781 Consumer and other — — — 59 59 Total $ 328 $ 3,962 $ 4,290 $ 69,864 $ 74,154 December 31, 2016 (in thousands) 30-89 Days Past Due 90 or More Past Due Total Past Due Current Total Commercial and industrial $ — $ — $ — $ 3,523 $ 3,523 Real estate: Commercial - investor owned — — — 8,162 8,162 Commercial - owner occupied — — — 11,863 11,863 Construction and land development — — — 4,365 4,365 Residential 169 51 220 11,572 11,792 Consumer and other — — — 64 64 Total $ 169 $ 51 $ 220 $ 39,549 $ 39,769

Derivative Financial Instrume38

Derivative Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2017
Risk Management
Derivative [Line Items]
Schedule of Notional Amounts and Fair Values of Derivative Instruments and Client-Related Derivative Instruments	The notional amount of the derivative instruments used to manage risk was $3.5 million at December 31, 2016 .
Client-Related
Derivative [Line Items]
Schedule of Notional Amounts and Fair Values of Derivative Instruments and Client-Related Derivative Instruments	The table below summarizes the notional amounts and fair values of the client-related derivative instruments. Asset Derivatives (Other Assets) Liability Derivatives (Other Liabilities) Notional Amount Fair Value Fair Value (in thousands) December 31, December 31, December 31, December 31, December 31, December 31, Non-designated hedging instruments Interest rate swap contracts $ 394,852 $ 124,322 $ 2,061 $ 982 $ 2,061 $ 982 Foreign exchange forward contracts 1,528 3,034 1,528 3,034 1,528 3,034

Fixed Assets (Tables)

Fixed Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Summary of Fixed Assets	A summary of fixed assets at December 31, 2017 and 2016 , is as follows: December 31, (in thousands) 2017 2016 Land $ 7,263 $ 3,103 Buildings and leasehold improvements 32,384 18,054 Furniture, fixtures and equipment 8,272 6,136 Capitalized software 1,305 1,305 49,224 28,598 Less accumulated depreciation and amortization 16,606 13,688 Total fixed assets $ 32,618 $ 14,910
Future Aggregate Minimum Rental Commitments	The future aggregate minimum rental commitments (in thousands) required under the Company's equipment and facilities leases are shown below: Year Amount 2018 $ 3,503 2019 3,477 2020 3,418 2021 3,337 2022 2,801 Thereafter 5,962 Total $ 22,498

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Summary of Intangible Assets	The table below presents a summary of intangible assets: (in thousands) Years ended December 31, 2017 2016 Gross core deposit intangible balance, beginning of year $ 9,060 $ 9,060 Additions 11,514 — Gross core deposit intangible, end of period 20,574 9,060 Accumulated amortization (9,518 ) (6,909 ) Core deposit intangible, net, end of year $ 11,056 $ 2,151
Expected Amortization Schedule for the Core Deposit Intangible	The following table reflects the expected amortization schedule for the core deposit intangible (in thousands) at December 31, 2017 . Year Core Deposit Intangible 2018 $ 2,504 2019 2,129 2020 1,755 2021 1,381 2022 1,071 After 2022 2,216 $ 11,056

Maturity of Certificates of D41

Maturity of Certificates of Deposit (Tables)	12 Months Ended
	Dec. 31, 2017
Maturities of Time Deposits [Abstract]
Summary of Certificates of Deposit Maturities	Following is a summary of certificates of deposit maturities at December 31, 2017 : (in thousands) Brokered Customer Total Less than 1 year $ 114,054 $ 317,373 $ 431,427 Greater than 1 year and less than 2 years 1,252 74,236 75,488 Greater than 2 years and less than 3 years — 48,553 48,553 Greater than 3 years and less than 4 years — 21,100 21,100 Greater than 4 years and less than 5 years — 1,598 1,598 Greater than 5 years — 607 607 $ 115,306 $ 463,467 $ 578,773

Subordinated Debentures (Tables

Subordinated Debentures (Tables)	12 Months Ended
	Dec. 31, 2017
Subordinated Borrowings [Abstract]
Schedule of Subordinated Debentures	The amounts and terms of each issuance of the Company's subordinated debentures at December 31, 2017 and 2016 were as follows: Amount Maturity Date Call Date Interest Rate (in thousands) 2017 2016 EFSC Clayco Statutory Trust I $ 3,196 $ 3,196 December 17, 2033 December 17, 2008 Floats 3MO LIBOR + 2.85% EFSC Capital Trust II 5,155 5,155 June 17, 2034 June 17, 2009 Floats 3MO LIBOR + 2.65% EFSC Statutory Trust III 11,341 11,341 December 15, 2034 December 15, 2009 Floats 3MO LIBOR + 1.97% EFSC Clayco Statutory Trust II 4,124 4,124 September 15, 2035 September 15, 2010 Floats 3MO LIBOR + 1.83% EFSC Statutory Trust IV 10,310 10,310 December 15, 2035 December 15, 2010 Floats 3MO LIBOR + 1.44% EFSC Statutory Trust V 4,124 4,124 September 15, 2036 September 15, 2011 Floats 3MO LIBOR + 1.60% EFSC Capital Trust VI 14,433 14,433 March 30, 2037 March 30, 2012 Floats 3MO LIBOR + 1.60% EFSC Capital Trust VII 4,124 4,124 December 15, 2037 December 15, 2012 Floats 3MO LIBOR + 2.25% JEFFCO Stat Trust I (1) 8,153 — February 22, 2031 February 22, 2011 Fixed 10.2% JEFFCO Stat Trust II (1) 4,281 — March 17, 2034 March 17, 2009 Floats 3MO LIBOR + 2.75% Total trust preferred securities 69,241 56,807 Fixed-to-floating rate subordinated notes 50,000 50,000 November 1, 2026 November 1, 2021 Fixed 4.75% until Debt issuance costs (1,136 ) (1,267 ) Total fixed-to-floating rate subordinated notes 48,864 48,733 Total subordinated debentures and notes $ 118,105 $ 105,540 (1) Purchase accounting adjustments are reflected in the balance and also impact the effective interest rate.

Federal Home Loan Bank Advanc43

Federal Home Loan Bank Advances (Tables)	12 Months Ended
	Dec. 31, 2017
Federal Home Loan Bank, Advances [Table Text Block]	The following table summarizes the type, maturity, and rate of the Company's FHLB advances at December 31: 2017 2016 ($ in thousands) Term Outstanding Balance Weighted Rate Outstanding Balance Weighted Rate Non-amortizing fixed advance Less than 1 year $ 172,743 1.56 % $ — — % Non-amortizing fixed advance Greater than 1 year — — % — — % Total Federal Home Loan Bank Advances $ 172,743 1.56 % $ — — %

Other Borrowings and Notes Pa44

Other Borrowings and Notes Payable (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Instrument [Line Items]
Schedule of Line of Credit Facilities [Table Text Block]	Revolving Credit In February 2016 , the Company entered into a senior unsecured revolving credit agreement ("Revolving Agreement") with another bank allowing for borrowings up to $20 million . The proceeds can be used for general corporate purposes. The Revolving Agreement is subject to ongoing compliance with a number of customary affirmative and negative covenants as well as specified financial covenants. A summary of the amounts drawn on the Revolving Agreement as of December 31, 2017 , and 2016 is as follows: December 31, ($ in thousands) 2017 2016 Outstanding balance $ — $ — Average balance during the year $ 822 $ — Maximum balance outstanding at any month-end 10,000 — Weighted average interest rate during the year 3.50 % — % Average interest rate at December 31 — % — %
Other Borrowings
Debt Instrument [Line Items]
Summary of Other Borrowings	A summary of other borrowings is as follows: December 31, ($ in thousands) 2017 2016 Securities sold under customer repurchase agreements $ 253,674 $ 276,980 Average balance during the year $ 220,807 $ 206,643 Maximum balance outstanding at any month-end 253,674 276,980 Average interest rate during the year 0.21 % 0.19 % Average interest rate at December 31 0.25 % 0.18 %

Regulatory Matters (Tables)

Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2017
Regulated Operations [Abstract]
Schedule of Actual Capital Amounts and Ratios	The actual capital amounts and ratios are presented in the table below: Actual For Capital Adequacy Purposes To Be Well Capitalized Under Applicable Action Provisions ($ in thousands) Amount Ratio Amount Ratio Amount Ratio As of December 31, 2017: Total Capital (to Risk Weighted Assets) Enterprise Financial Services Corp $ 589,047 12.21 % $ 385,816 8.00 % $ — — % Enterprise Bank & Trust 546,314 11.36 384,791 8.00 480,989 10.00 Tier 1 Capital (to Risk Weighted Assets) Enterprise Financial Services Corp 496,045 10.29 289,362 6.00 — — Enterprise Bank & Trust 503,312 10.46 288,593 6.00 384,791 8.00 Common Equity Tier 1 Capital (to Risk Weighted Assets) Enterprise Financial Services Corp 428,397 8.88 217,021 4.50 — — Enterprise Bank & Trust 503,264 10.46 216,445 4.50 312,643 6.50 Leverage Ratio (Tier 1 Capital to Average Assets) Enterprise Financial Services Corp 496,045 9.72 204,087 4.00 — — Enterprise Bank & Trust 503,312 9.68 207,885 4.00 259,856 5.00 As of December 31, 2016: Total Capital (to Risk Weighted Assets) Enterprise Financial Services Corp $ 506,349 13.48 % $ 300,573 8.00 % $ — — % Enterprise Bank & Trust 430,981 11.53 298,982 8.00 373,728 10.00 Tier 1 Capital (to Risk Weighted Assets) Enterprise Financial Services Corp 412,865 10.99 225,430 6.00 — — Enterprise Bank & Trust 387,497 10.37 224,237 6.00 298,982 8.00 Common Equity Tier 1 Capital (to Risk Weighted Assets) Enterprise Financial Services Corp 357,729 9.52 169,072 4.50 — — Enterprise Bank & Trust 387,461 10.37 168,178 4.50 242,923 6.50 Leverage Ratio (Tier 1 Capital to Average Assets) Enterprise Financial Services Corp 412,865 10.42 158,480 4.00 — — Enterprise Bank & Trust 387,497 9.81 157,933 4.00 197,417 5.00

Compensation Plans (Tables)

Compensation Plans (Tables)	12 Months Ended
	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding Long Term Incentive Awards [Table Text Block]	Information related to the outstanding grants at December 31, 2017 is shown below: (in thousands, except share and per share data) 2016 - 2018 Cycle 2017 - 2019 Cycle Shares issuable at target 87,758 55,203 Maximum shares issuable 107,955 68,263 Unrecognized compensation cost $ 949 $ 1,792 Weighted average grant date fair value 25.26 40.72
Summary of Employee Stock Option and SSARs Activity	Following is a summary of the employee stock option and SSAR activity for 2017 . (in thousands, except share and per share data) Shares Weighted Weighted Aggregate Outstanding at December 31, 2016 270,246 $ 18.85 Granted — — Exercised (164,116 ) 22.40 Forfeited — — Outstanding at December 31, 2017 106,130 $ 13.37 1.9 years $ 3,373 Exercisable at December 31, 2017 106,130 $ 13.37 1.9 years $ 3,373
Summary of Restricted Stock Units Activity	A summary of the status of the Company's RSU awards as of December 31, 2017 and changes during the year then ended is presented below. Shares Weighted Average Grant Date Fair Value Outstanding at December 31, 2016 58,698 $ 23.06 Granted 16,462 41.68 Vested (33,206 ) 18.48 Forfeited (732 ) 14.48 Outstanding at December 31, 2017 41,222 $ 34.34
Stock Options and SSARs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Various Information	Various information related to the stock options and SSARs is shown below. (in thousands) 2017 2016 2015 Compensation expense $ — $ — $ 50 Intrinsic value of option exercises on date of exercise 3,156 1,156 74 Cash received from the exercise of stock options 91 87 126
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Various Information	Various information related to the RSUs is shown below. ($ in thousands) 2017 2016 2015 Compensation expense $ 898 $ 850 $ 725 Total fair value at vesting date 1,471 2,275 809 Total unrecognized compensation cost for nonvested stock units 837 1,084 942 Expected years to recognize unearned compensation 1.8 years 1.6 years 1.7 years
Stock Plan for Non-Management Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Various Information	Various information related to the Director Plan is shown below. (in thousands, except share and per share data) 2017 2016 2015 Shares issued 10,531 12,528 16,283 Weighted average fair value $ 42.46 $ 31.25 $ 24.43 Compensation expense 397 407 373

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit)	The components of income tax expense for the years ended December 31 are as follows: Years ended December 31, (in thousands) 2017 2016 2015 Current: Federal $ 15,845 $ 17,005 $ 22,916 State and local 1,377 1,734 2,798 Total current 17,222 18,739 25,714 Deferred: Federal 20,989 5,959 (5,266 ) State and local 116 1,304 (497 ) Total deferred 21,105 7,263 (5,763 ) Total income tax expense $ 38,327 $ 26,002 $ 19,951
Schedule of Income Tax Rate Reconciliation	A reconciliation of expected income tax expense, computed by applying the statutory federal income tax rate in 2017 , 2016 , and 2015 to income before income taxes and the amounts reflected in the consolidated statements of operations is as follows: Years ended December 31, (in thousands) 2017 2016 2015 Income tax expense at statutory rate $ 30,281 $ 26,194 $ 20,440 Increase (reduction) in income tax resulting from: Tax-exempt income, net (961 ) (945 ) (931 ) State and local income taxes, net 1,676 1,673 1,414 Bank-owned life insurance, net (715 ) (544 ) (462 ) Non-deductible expenses 407 263 259 Change in estimated rate for deferred taxes 12,117 302 — Tax benefits of LIHTC investments, net (257 ) (181 ) (179 ) Excess tax benefits (2,141 ) — — Other federal tax benefits (1,701 ) — — Other, net (379 ) (760 ) (590 ) Total income tax expense $ 38,327 $ 26,002 $ 19,951
Schedule of Deferred Tax Assets and Deferred Tax Liabilities	The tax effect of temporary differences that gave rise to significant portions of the deferred tax assets and deferred tax liabilities is as follows: Years ended December 31, (in thousands) 2017 2016 Deferred tax assets: Allowance for loan losses $ 10,516 $ 16,496 Basis difference on PCI assets, net 5,748 5,551 Basis difference on Other real estate 694 317 Deferred compensation 2,719 4,217 Goodwill and other intangible assets 2,151 5,520 Accrued compensation 646 899 Unrealized losses on securities available for sale 1,490 1,019 Other, net 2,150 925 Total deferred tax assets 26,114 34,944 Deferred tax liabilities: State tax credits held for sale, net of economic hedge 26 376 Core deposit intangibles 2,731 817 Other, net 855 — Total deferred tax liabilities 3,612 1,193 Net deferred tax asset $ 22,502 $ 33,751 Deferred tax rate 24.7 % 38.0 %
Schedule of Unrecognized Tax Benefits	The activity in the gross liability for unrecognized tax benefits was as follows: (in thousands) 2017 2016 2015 Balance at beginning of year $ 1,180 $ 1,359 $ 1,884 Additions based on tax positions related to the current year 331 239 230 Additions for tax positions of prior years 41 39 46 Reductions for tax positions of prior years — — (437 ) Settlements or lapse of statute of limitations (308 ) (457 ) (364 ) Balance at end of year $ 1,244 $ 1,180 $ 1,359

Commitments (Tables)

Commitments (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of Commitments	The contractual amounts of off-balance-sheet financial instruments as of December 31, 2017 , and December 31, 2016 , are as follows: (in thousands) December 31, 2017 December 31, 2016 Commitments to extend credit $ 1,298,423 $ 1,075,170 Letters of credit 73,790 78,954

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Summary of Financial Instruments Measured at Fair Value on a Recurring Basis	The following table summarizes financial instruments measured at fair value on a recurring basis as of December 31, 2017 and 2016 , segregated by the level of the valuation inputs within the fair value hierarchy utilized to measure fair value. December 31, 2017 (in thousands) Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Fair Value Assets Securities available for sale Obligations of U.S. Government-sponsored enterprises $ — $ 99,224 $ — $ 99,224 Obligations of states and political subdivisions — 34,642 — 34,642 Residential mortgage-backed securities — 507,516 — 507,516 Total securities available for sale — 641,382 — 641,382 State tax credits held for sale — — 400 400 Derivative financial instruments — 3,589 — 3,589 Total assets $ — $ 644,971 $ 400 $ 645,371 Liabilities Derivative financial instruments $ — $ 3,589 $ — $ 3,589 Total liabilities $ — $ 3,589 $ — $ 3,589 December 31, 2016 (in thousands) Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Fair Value Assets Securities available for sale Obligations of U.S. Government-sponsored enterprises $ — $ 107,660 $ — $ 107,660 Obligations of states and political subdivisions — 33,542 3,089 36,631 Residential mortgage-backed securities — 316,506 — 316,506 Total securities available for sale — 457,708 3,089 460,797 State tax credits held for sale — — 3,585 3,585 Derivative financial instruments — 4,016 — 4,016 Total assets $ — $ 461,724 $ 6,674 $ 468,398 Liabilities Derivative financial instruments $ — $ 4,016 $ — $ 4,016 Total liabilities $ — $ 4,016 $ — $ 4,016
Schedule of Level 3 Financial Instruments Measured at Fair Value on a Recurring Basis	The following table presents the changes in Level 3 financial instruments measured at fair value on a recurring basis as of December 31, 2017 and 2016 . • Purchases, sales, issuances and settlements . There were no Level 3 purchases during the years ended December 31, 2017 and 2016 . • Transfers in and/or out of Level 3 . There was $3.1 million in Level 3 transfers to Level 2 for the year ending December 31, 2017 because more observable market data became available for the Auction Rate Securities. The Company's policy is to recognize transfers into or out of a level as of the end of a reporting period. As a result, the transfers occurred on June 30, 2017. There were no transfers in and/or out of Level 3 for the year ending 2016 . Securities available for sale, at fair value Years ended December 31, (in thousands) 2017 2016 Beginning balance $ 3,089 $ 3,077 Total gains: Included in other comprehensive income 4 12 Transfer in and/or out of Level 3 (3,093 ) — Ending balance $ — $ 3,089 Change in unrealized gains relating to assets still held at the reporting date $ — $ 12 State tax credits held for sale, at fair value Years ended December 31, (in thousands) 2017 2016 Beginning balance $ 3,585 $ 5,941 Total gains: Included in earnings 101 177 Purchases, sales, issuances and settlements: Sales (3,286 ) (2,533 ) Ending balance $ 400 $ 3,585 Change in unrealized losses relating to assets still held at the reporting date $ (885 ) $ (575 )
Summary of Financial Instruments and Non-Financial Assets Measured at Fair Value on a Non-Recurring Basis	The following table presents financial instruments and non-financial assets measured at fair value on a non-recurring basis as of December 31, 2017 and 2016 . December 31, 2017 (1) (1) (1) (1) (in thousands) Total Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant (Level 3) Total losses for the year ended Impaired loans $ 3,200 $ — $ — $ 3,200 $ 6,599 Other real estate — — — — — Total $ 3,200 $ — $ — $ 3,200 $ 6,599 December 31, 2016 (1) (1) (1) (1) (in thousands) Total Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant (Level 3) Total losses for the year ended Impaired loans $ 175 $ — $ — $ 175 $ 4,335 Other real estate — — — — 1 Total $ 175 $ — $ — $ 175 $ 4,336 (1) The amounts represent only balances measured at fair value during the period and still held as of the reporting date.
Summary of Carrying Amount and Fair Values of Financial Instruments Reported on the Balance Sheets	Following is a summary of the carrying amounts and fair values of the Company’s financial instruments on the consolidated balance sheets at December 31, 2017 and 2016 . December 31, 2017 December 31, 2016 (in thousands) Carrying Amount Estimated fair value Carrying Amount Estimated fair value Balance sheet assets Cash and due from banks $ 91,084 $ 91,084 $ 54,288 $ 54,288 Federal funds sold 1,223 1,223 446 446 Interest-bearing deposits 63,661 63,661 145,048 145,048 Securities available for sale 641,382 641,382 460,797 460,797 Securities held to maturity 73,749 73,458 80,463 79,639 Other investments, at cost 26,661 26,661 14,840 14,840 Loans held for sale 3,155 3,155 9,562 9,562 Derivative financial instruments 3,589 3,589 4,016 4,016 Portfolio loans, net 4,054,473 4,096,741 3,114,752 3,125,701 State tax credits, held for sale 43,468 44,271 38,071 41,264 Accrued interest receivable 14,069 14,069 11,117 11,117 Balance sheet liabilities Deposits 4,156,414 4,153,323 3,233,361 3,232,414 Subordinated debentures and notes 118,105 105,031 105,540 86,052 Federal Home Loan Bank advances 172,743 172,893 — — Other borrowings 253,674 253,530 276,980 276,905 Derivative financial instruments 3,589 3,589 4,016 4,016 Accrued interest payable 1,730 1,730 1,105 1,105
Schedule of Estimated Fair Values of Financial Instruments Not Recorded at Fair Value on Balance Sheet	The following table presents the level in the fair value hierarchy for the estimated fair values of only the Company’s financial instruments that are not already on the consolidated balance sheets at fair value at December 31, 2017 , and December 31, 2016 . Estimated Fair Value Measurement at Reporting Date Using Balance at (in thousands) Level 1 Level 2 Level 3 Financial Assets: Securities held to maturity $ — $ 73,458 $ — $ 73,458 Portfolio loans, net — — 4,096,741 4,096,741 State tax credits, held for sale — — 43,871 43,871 Financial Liabilities: Deposits 3,577,641 — 575,682 4,153,323 Subordinated debentures and notes — 105,031 — 105,031 Federal Home Loan Bank advances — 172,893 — 172,893 Other borrowings — 253,530 — 253,530 Estimated Fair Value Measurement at Reporting Date Using Balance at (in thousands) Level 1 Level 2 Level 3 Financial Assets: Securities held to maturity $ — $ 79,639 $ — $ 79,639 Portfolio loans, net — — 3,125,701 3,125,701 State tax credits, held for sale — — 37,679 37,679 Financial Liabilities: Deposits 2,760,202 — 472,212 3,232,414 Subordinated debentures and notes — 86,052 — 86,052 Federal Home Loan Bank advances — — — — Other borrowings — 276,905 — 276,905

Parent Company Only Condensed50

Parent Company Only Condensed Financial Statements (Tables)	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Balance Sheets	Condensed Balance Sheets December 31, (in thousands) 2017 2016 Assets Cash $ 9,977 $ 52,245 Investment in Enterprise Bank & Trust 623,439 416,831 Investment in nonbank subsidiaries 6,546 2,798 Other assets 28,741 22,111 Total assets $ 668,703 $ 493,985 Liabilities and Shareholders' Equity Subordinated debentures and notes $ 118,105 $ 105,540 Accounts payable and other liabilities 2,025 1,347 Shareholders' equity 548,573 387,098 Total liabilities and shareholders' equity $ 668,703 $ 493,985
Condensed Statements of Operations	Condensed Statements of Operations Years ended December 31, (in thousands) 2017 2016 2015 Income: Dividends from subsidiaries $ 20,000 $ 7,500 $ 10,000 Other 708 491 249 Total income 20,708 7,991 10,249 Expenses: Interest expense-subordinated debentures and notes 5,094 1,893 1,248 Interest expense-notes payable 89 53 144 Other expenses 5,486 5,526 3,823 Total expenses 10,669 7,472 5,215 Income before taxes and equity in undistributed earnings of subsidiaries 10,039 519 5,034 Income tax benefit 3,098 2,583 2,118 Net income before equity in undistributed earnings of subsidiaries 13,137 3,102 7,152 Equity in undistributed earnings of subsidiaries 35,053 45,735 31,298 Net income and comprehensive income $ 48,190 $ 48,837 $ 38,450
Condensed Statements of Cash Flow	Condensed Statements of Cash Flows Years Ended December 31, (in thousands) 2017 2016 2015 Cash flows from operating activities: Net income $ 48,190 $ 48,837 $ 38,450 Adjustments to reconcile net income to net cash provided by (used in) operating activities: Share-based compensation 3,427 3,367 3,601 Net income of subsidiaries (55,053 ) (53,235 ) (41,298 ) Dividends from subsidiaries 20,000 7,500 10,000 Excess tax expense of share-based compensation — (1,327 ) (449 ) Other, net (1,806 ) 1,848 848 Net cash provided by operating activities 14,758 6,990 11,152 Cash flows from investing activities: Cash contributions to subsidiaries — (250 ) — Cash paid for acquisitions, net of cash acquired (25,187 ) — — Purchases of other investments (3,679 ) (2,435 ) (2,832 ) Proceeds from distributions on other investments 1,634 1,151 880 Net cash used by investing activities (27,232 ) (1,534 ) (1,952 ) Cash flows from financing activities: Proceeds from issuance of subordinated notes — 48,733 — Proceeds from notes payable 10,000 — — Repayments of notes payable (10,000 ) — (5,700 ) Cash dividends paid (10,249 ) (8,211 ) (5,259 ) Excess tax benefit of share-based compensation — 1,327 449 Payments for the repurchase of common stock (16,636 ) (4,889 ) — Payments for the issuance of equity instruments, net (2,909 ) (2,203 ) (1,190 ) Net cash provided (used) by financing activities (29,794 ) 34,757 (11,700 ) Net increase (decrease) in cash and cash equivalents (42,268 ) 40,213 (2,500 ) Cash and cash equivalents, beginning of year 52,245 12,032 14,532 Cash and cash equivalents, end of year $ 9,977 $ 52,245 $ 12,032 Supplemental disclosures of cash flow information: Noncash transactions: Common shares issued in connection with JCB acquisition $ 141,729 $ — $ —

Quarterly Condensed Financial51

Quarterly Condensed Financial Information (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	The following table presents unaudited quarterly financial information for the periods indicated: 2017 (in thousands, except per share data) 4th Quarter 3rd Quarter 2nd Quarter 1st Quarter Interest income $ 54,789 $ 52,468 $ 51,542 $ 43,740 Interest expense 7,385 6,843 5,909 5,098 Net interest income 47,404 45,625 45,633 38,642 Provision for portfolio loan losses 3,186 2,422 3,623 1,533 Provision reversal for purchased credit impaired loan losses (279 ) — (207 ) (148 ) Net interest income after provision for loan losses 44,497 43,203 42,217 37,257 Noninterest income 11,112 8,372 7,934 6,976 Noninterest expense 28,260 27,404 32,651 26,736 Income before income tax expense 27,349 24,171 17,500 17,497 Income tax expense 19,820 7,856 5,545 5,106 Net income $ 7,529 $ 16,315 $ 11,955 $ 12,391 Earnings per common share: Basic $ 0.33 $ 0.70 $ 0.51 $ 0.57 Diluted 0.32 0.69 0.50 0.56 2016 (in thousands, except per share data) 4th Quarter 3rd Quarter 2nd Quarter 1st Quarter Interest income $ 39,438 $ 37,293 $ 37,033 $ 35,460 Interest expense 3,984 3,463 3,250 3,032 Net interest income 35,454 33,830 33,783 32,428 Provision for portfolio loan losses 964 3,038 716 833 Provision reversal for purchased credit impaired loan losses (343 ) (1,194 ) (336 ) (73 ) Net interest income after provision for loan losses 34,833 31,986 33,403 31,668 Noninterest income 9,029 6,976 7,049 6,005 Noninterest expense 23,181 20,814 21,353 20,762 Income before income tax expense 20,681 18,148 19,099 16,911 Income tax expense 7,053 6,316 6,747 5,886 Net income $ 13,628 $ 11,832 $ 12,352 $ 11,025 Earnings per common share: Basic $ 0.68 $ 0.59 $ 0.62 $ 0.55 Diluted 0.67 0.59 0.61 0.54

Summary of Significant Accoun52

Summary of Significant Accounting Policies (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)segment	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Property, Plant and Equipment [Line Items]
Number of reportable segments | segment	1
Required reserves on deposits maintained	$ 17.5	$ 18.2
Minimum period of consecutive contractual payments to no longer be considered in nonaccrual status	6 years
Removal of remaining clawback liability, FDIC loss share termination			$ 3.5
Removal of remaining FDIC receivable, FDIC loss share termination			$ 7.2
Finite-lived intangible assets useful life	10 years	10 years
Furniture, Fixtures and Equipment [Member] | Minimum
Property, Plant and Equipment [Line Items]
Property plant and equipment useful life	3 years
Furniture, Fixtures and Equipment [Member] | Maximum
Property, Plant and Equipment [Line Items]
Property plant and equipment useful life	10 years
Building and Leasehold Improvements [Member] | Minimum
Property, Plant and Equipment [Line Items]
Property plant and equipment useful life	10 years
Building and Leasehold Improvements [Member] | Maximum
Property, Plant and Equipment [Line Items]
Property plant and equipment useful life	40 years
Software [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment useful life	3 years
Core Deposits [Member]
Property, Plant and Equipment [Line Items]
Finite-lived intangible assets useful life	10 years
State and Local Jurisdiction [Member]
Property, Plant and Equipment [Line Items]
Right to receive state tax credit at agreed upon rates	10 years

Acquisitions & Divestitures - N

Acquisitions & Divestitures - Narrative (Details)	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Feb. 10, 2017USD ($)$ / shares	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of operating JCB branches			13
Total shares awarded to JCB shareholders		0	3,299,864	0
Sale of Stock, Consideration Received Per Transaction | $ / shares			$ 85.39
EFSC common stock offered per share of JCB common stock			2.75
Total cash paid to JCB shareholders and holders of JCB stock options			$ 29,300,000
EFSC Closing Stock Price			42.95
Transaction value including JCB's common stock and stock options			171,000,000
Business Combination, Acquisition Related Costs	$ 6,500,000	$ 1,400,000
Business Acquisition, Goodwill, Expected Tax Deductible Amount			$ 87,000,000
Fair Value Discount Recorded to Portfolio Loans	$ 24,700,000

Acquisitions & Divestitures - S

Acquisitions & Divestitures - Summary of Balance Sheet Amounts Relative to Branches Sold (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2017USD ($)$ / shares	Dec. 31, 2016USD ($)$ / shares	Dec. 31, 2015USD ($)	Feb. 10, 2017USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash, Cash Equivalents, and Federal Funds Sold	$ 153,323,000				$ 198,802,000				$ 153,323,000	$ 198,802,000
Loans and Leases Receivable, Net Amount	4,054,473,000				3,114,752,000				4,054,473,000	3,114,752,000
Fixed assets, net	32,618,000				14,910,000				32,618,000	14,910,000
Accrued interest receivable	14,069,000				11,117,000				14,069,000	11,117,000
Goodwill	117,345,000				30,334,000				117,345,000	30,334,000	$ 30,334,000
Intangible assets, net	11,056,000				2,151,000				11,056,000	2,151,000
Deposits	4,156,414,000				3,233,361,000				4,156,414,000	3,233,361,000
Other borrowings	253,674,000				276,980,000				253,674,000	276,980,000
Investments trust preferred securities	2,100,000								2,100,000
Accrued interest payable	1,730,000				1,105,000				1,730,000	1,105,000
Other liabilities	37,986,000				77,244,000				37,986,000	77,244,000
Total cash paid to JCB shareholders and holders of JCB stock options												$ 29,300,000
Net income	7,529,000	$ 16,315,000	$ 11,955,000	$ 12,391,000	$ 13,628,000	$ 11,832,000	$ 12,352,000	$ 11,025,000	48,190,000	48,837,000	$ 38,450,000
Transaction value including JCB's common stock and stock options												171,000,000
Business Acquisition, Goodwill, Expected Tax Deductible Amount												87,000,000
Pro Forma [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenues									213,910,000	199,033,000
Net income									$ 47,227,000	$ 56,994,000
Diluted Earnings Per Share Pro Forma | $ / shares									$ 2.03	$ 2.42
As Recorded by JCB [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash, Cash Equivalents, and Federal Funds Sold												33,739,000
Interest-bearing Deposit Liabilities												1,715,000
Secured borrowings												148,670,000
Loans and Leases Receivable, Net Amount												685,905,000
Other Real Estate												6,762,000
Other Investments												2,695,000
Fixed assets, net												21,780,000
Accrued interest receivable												2,794,000
Goodwill												7,806,000
Intangible assets, net												25,000
Deferred Tax Assets, State Taxes												4,634,000
Other assets												19,107,000
Total assets acquired												935,632,000
Deposits												764,539,000
Other borrowings												55,430,000
Investments trust preferred securities												12,887,000
Accrued interest payable												653,000
Other liabilities												5,006,000
Total Liabilities Assumed												838,515,000
Net assets acquired (assumed)												97,117,000
Adjustments associated with acquisition [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash, Cash Equivalents, and Federal Funds Sold												0
Interest-bearing Deposit Liabilities												0
Secured borrowings												0
Loans and Leases Receivable, Net Amount												(11,094,000)
Other Real Estate												(5,082,000)
Other Investments												0
Fixed assets, net												(3,325,000)
Accrued interest receivable												0
Goodwill												(7,806,000)
Intangible assets, net												11,489,000
Deferred Tax Assets, State Taxes												3,991,000
Other assets												(296,000)
Total assets acquired												(12,123,000)
Deposits												629,000
Other borrowings												681,000
Investments trust preferred securities												(382,000)
Accrued interest payable												0
Other liabilities												65,000
Total Liabilities Assumed												993,000
Net assets acquired (assumed)												(13,116,000)
As Recorded by EFSC [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash, Cash Equivalents, and Federal Funds Sold												33,739,000
Interest-bearing Deposit Liabilities												1,715,000
Secured borrowings												148,670,000
Loans and Leases Receivable, Net Amount												674,811,000
Other Real Estate												1,680,000
Other Investments												2,695,000
Fixed assets, net												18,455,000
Accrued interest receivable												2,794,000
Goodwill												0
Intangible assets, net												11,514,000
Deferred Tax Assets, State Taxes	$ 8,600,000								$ 8,600,000			8,625,000
Other assets												18,811,000
Total assets acquired												923,509,000
Deposits												765,168,000
Other borrowings												56,111,000
Investments trust preferred securities												12,505,000
Accrued interest payable												653,000
Other liabilities												5,071,000
Total Liabilities Assumed												839,508,000
Net assets acquired (assumed)												84,001,000
Total cash paid to JCB shareholders and holders of JCB stock options												$ 29,283,000
Common shares issued in relation to acquisition												141,729,000
Transaction value including JCB's common stock and stock options												$ 171,000,000
Business Acquisition, Goodwill, Expected Tax Deductible Amount												$ 87,011,000

Earnings Per Share (Details)

Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share
Net income as reported	$ 7,529	$ 16,315	$ 11,955	$ 12,391	$ 13,628	$ 11,832	$ 12,352	$ 11,025	$ 48,190	$ 48,837	$ 38,450
Impact of assumed conversions
Weighted average common shares outstanding (in shares)									22,953,000	20,003,000	19,984,000
Additional dilutive common stock equivalents (in shares)									296,000	287,000	333,000
Weighted average diluted common shares outstanding (in shares)									23,249,000	20,290,000	20,317,000
Basic earnings per common share (in dollars per share)	$ 0.33	$ 0.70	$ 0.51	$ 0.57	$ 0.68	$ 0.59	$ 0.62	$ 0.55	$ 2.10	$ 2.44	$ 1.92
Diluted earnings per common share (in dollars per share)	$ 0.32	$ 0.69	$ 0.50	$ 0.56	$ 0.67	$ 0.59	$ 0.61	$ 0.54	$ 2.07	$ 2.41	$ 1.89
Common stock equivalents excluded from earnings per share calculations due to anti-dilutive effect (in shares)									0	0	79,670
Convertible Debt Securities
Debt Instrument, Interest Rate, Stated Percentage [Abstract]
Convertible trust preferred securities, interest rate, stated percentage	9.00%				9.00%				9.00%	9.00%	9.00%

Investments - Schedule of Avail

Investments - Schedule of Available-for-sale and Held-to-Maturity Securities Reconciliation (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 73,749	$ 80,463
Gross Unrealized Gains	85	56
Gross Unrealized Losses	(376)	(880)
Fair Value	73,458	79,639
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	647,141	463,143
Gross Unrealized Gains	1,407	2,079
Gross Unrealized Losses	(7,166)	(4,425)
Fair Value	641,382	460,797
Obligations of U.S. Government-sponsored enterprises
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	99,878	107,312
Gross Unrealized Gains	6	348
Gross Unrealized Losses	(660)	0
Fair Value	99,224	107,660
Obligations of states and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	34,181	36,486
Gross Unrealized Gains	674	630
Gross Unrealized Losses	(213)	(485)
Fair Value	34,642	36,631
Residential mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	513,082	319,345
Gross Unrealized Gains	727	1,101
Gross Unrealized Losses	(6,293)	(3,940)
Fair Value	507,516	316,506
Obligations of states and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	14,031	14,759
Gross Unrealized Gains	69	11
Gross Unrealized Losses	(46)	(242)
Fair Value	14,054	14,528
Residential mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	59,718	65,704
Gross Unrealized Gains	16	45
Gross Unrealized Losses	(330)	(638)
Fair Value	$ 59,404	$ 65,111

Investments - Investments Class

Investments - Investments Classified by Contractual Maturity Date (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Available for sale, Amortized Cost
Due in one year or less	$ 3,060
Due after one year through five years	110,910
Due after five years through ten years	14,573
Due after ten years	5,516
Agency mortgage-backed securities	513,082
Amortized Cost	647,141	$ 463,143
Available for sale, Estimated Fair Value
Due in one year or less	3,076
Due after one year through five years	110,480
Due after five years through ten years	14,980
Due after ten years	5,330
Agency mortgage-backed securities	507,516
Securities available for sale	641,382	460,797
Held to maturity, Amortized Cost
Due in one year or less	0
Due after one year through five years	186
Due after five years through ten years	12,977
Due after ten years	868
Agency mortgage-backed securities	59,718
Amortized Cost	73,749	80,463
Held to maturity, Estimated Fair Value
Due in one year or less	0
Due after one year through five years	195
Due after five years through ten years	12,981
Due after ten years	878
Agency mortgage-backed securities	59,404
Held to maturity, fair value	$ 73,458	$ 79,639

Investments - Schedule of Unrea

Investments - Schedule of Unrealized Loss on Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, fair value	$ 572,915	$ 289,095
Less than 12 months, unrealized losses	(6,953)	(4,492)
12 months or more, fair value	12,229	16,436
12 months or more, unrealized losses	(589)	(813)
Total, fair value	585,144	305,531
Total, unrealized losses	(7,542)	(5,305)
Obligations of U.S. Government-sponsored enterprises
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, fair value	89,309
Less than 12 months, unrealized losses	660
12 months or more, fair value	0
12 months or more, unrealized losses	0
Total, fair value	89,309
Total, unrealized losses	660
Obligations of states and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, fair value	13,951	21,361
Less than 12 months, unrealized losses	259	408
12 months or more, fair value	0	3,553
12 months or more, unrealized losses	0	320
Total, fair value	13,951	24,914
Total, unrealized losses	259	728
Agency mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, fair value	469,655	267,734
Less than 12 months, unrealized losses	6,034	4,084
12 months or more, fair value	12,229	12,883
12 months or more, unrealized losses	589	493
Total, fair value	481,884	280,617
Total, unrealized losses	$ 6,623	$ 4,577

Investments - Schedule of Reali

Investments - Schedule of Realized Gain (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Gross gains realized	$ 22	$ 86	$ 63
Gross losses realized	0	0	(40)
Proceeds from sales	$ 144,076	$ 2,493	$ 41,069

Investments - Narrative (Detail

Investments - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Other investments, at cost	$ 26,661	$ 14,840
Maximum percentage of shareholders' equity security holdings held of one issuer	10.00%
Available-for-sale securities pledged as collateral, fair value	$ 500,000	407,300
Mortgage-backed securities, weighted average life	4 years
Des Moines
Schedule of Available-for-sale Securities [Line Items]
Other investments, at cost	$ 12,900	$ 4,400

Portfolio Loans - Summary of Po

Portfolio Loans - Summary of Portfolio Loans by Category (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, including unearned loan fees	$ 4,097,050	$ 3,158,161
Non-Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, before unearned loan (fees) costs	4,024,221	3,119,154
Unearned loan (fees) costs, net	(1,325)	(762)
Loans, including unearned loan fees	4,022,896	3,118,392
Non-Covered Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, before unearned loan (fees) costs	1,918,720	1,632,714
Non-Covered Loans | CRE - investor owned
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, before unearned loan (fees) costs	769,275	544,808
Non-Covered Loans | CRE - owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, before unearned loan (fees) costs	554,589	350,148
Non-Covered Loans | Construction and land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, before unearned loan (fees) costs	303,091	194,542
Non-Covered Loans | Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, before unearned loan (fees) costs	341,312	240,760
Non-Covered Loans | Total real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, before unearned loan (fees) costs	1,968,267	1,330,258
Non-Covered Loans | Consumer and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, before unearned loan (fees) costs	137,234	156,182
Loans, including unearned loan fees	$ 135,909	$ 155,420

Portfolio Loans - Summary of Lo

Portfolio Loans - Summary of Loans to Executive Officers and Directors (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Loans and Leases Receivable, Related Parties [Roll Forward]
Balance at beginning of year	$ 15,406	$ 4,394	$ 13,513
New loans and advances	1,353	11,539	641
Payments and other reductions	(11,410)	(527)	(9,760)
Balance at end of year	$ 5,349	$ 15,406	$ 4,394

Portfolio Loans - Summary of Al

Portfolio Loans - Summary of Allowance for Loan Losses by Portfolio Class and Category (Details) - Non-Covered Loans - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Loan Losses [Roll Forward]
Balance, beginning of year	$ 37,565	$ 33,441	$ 30,185
Provision (provision reversal)	10,764	5,551	4,872
Losses charged off	(11,507)	(4,335)	(6,091)
Recoveries	1,344	2,908	4,475
Balance, end of year	38,166	37,565	33,441
Commercial and industrial
Allowance for Loan Losses [Roll Forward]
Balance, beginning of year	26,996	22,056	16,983
Provision (provision reversal)	8,737	6,569	6,976
Losses charged off	(9,872)	(2,303)	(3,699)
Recoveries	545	674	1,796
Balance, end of year	26,406	26,996	22,056
CRE - investor owned
Allowance for Loan Losses [Roll Forward]
Balance, beginning of year	3,420	3,484	4,382
Provision (provision reversal)	456	(11)	(303)
Losses charged off	(117)	(95)	(664)
Recoveries	131	42	69
Balance, end of year	3,890	3,420	3,484
CRE - owner occupied
Allowance for Loan Losses [Roll Forward]
Balance, beginning of year	2,890	2,969	3,135
Provision (provision reversal)	404	(1,202)	(1,626)
Losses charged off	(90)	0	(38)
Recoveries	104	1,123	1,498
Balance, end of year	3,308	2,890	2,969
Construction and land development
Allowance for Loan Losses [Roll Forward]
Balance, beginning of year	1,304	1,704	1,715
Provision (provision reversal)	336	(1,334)	(335)
Losses charged off	(254)	0	(350)
Recoveries	101	934	674
Balance, end of year	1,487	1,304	1,704
Residential real estate
Allowance for Loan Losses [Roll Forward]
Balance, beginning of year	2,023	1,796	2,830
Provision (provision reversal)	797	129	(58)
Losses charged off	(973)	(25)	(1,313)
Recoveries	390	123	337
Balance, end of year	2,237	2,023	1,796
Consumer and other
Allowance for Loan Losses [Roll Forward]
Balance, beginning of year	932	1,432	1,140
Provision (provision reversal)	34	1,400	218
Losses charged off	(201)	(1,912)	(27)
Recoveries	73	12	101
Balance, end of year	$ 838	$ 932	$ 1,432

Portfolio Loans - Summary of Re

Portfolio Loans - Summary of Recorded Investment in Portfolio Loans by Class and Category Based on Impairment Method (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Loans - Ending balance:
Loans, including unearned loan fees	$ 4,097,050	$ 3,158,161
Non-Covered Loans
Balance December 31, 2017
Individually evaluated for impairment	2,579	3,064
Collectively evaluated for impairment	35,587	34,501
Total	38,166	37,565	$ 33,441	$ 30,185
Loans - Ending balance:
Individually evaluated for impairment	17,175	16,772
Collectively evaluated for impairment	4,005,721	3,101,620
Loans, including unearned loan fees	4,022,896	3,118,392
Total	4,024,221	3,119,154
Non-Covered Loans | Commercial and industrial
Balance December 31, 2017
Individually evaluated for impairment	2,508	2,909
Collectively evaluated for impairment	23,898	24,087
Total	26,406	26,996	22,056	16,983
Loans - Ending balance:
Individually evaluated for impairment	12,665	12,523
Collectively evaluated for impairment	1,906,055	1,620,191
Total	1,918,720	1,632,714
Non-Covered Loans | CRE - investor owned
Balance December 31, 2017
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	3,890	3,420
Total	3,890	3,420	3,484	4,382
Loans - Ending balance:
Individually evaluated for impairment	422	430
Collectively evaluated for impairment	768,853	544,378
Total	769,275	544,808
Non-Covered Loans | CRE - owner occupied
Balance December 31, 2017
Individually evaluated for impairment	71	0
Collectively evaluated for impairment	3,237	2,890
Total	3,308	2,890	2,969	3,135
Loans - Ending balance:
Individually evaluated for impairment	1,975	1,854
Collectively evaluated for impairment	552,614	348,294
Total	554,589	350,148
Non-Covered Loans | Construction and land development
Balance December 31, 2017
Individually evaluated for impairment	0	155
Collectively evaluated for impairment	1,487	1,149
Total	1,487	1,304	1,704	1,715
Loans - Ending balance:
Individually evaluated for impairment	136	1,903
Collectively evaluated for impairment	302,955	192,639
Total	303,091	194,542
Non-Covered Loans | Residential real estate
Balance December 31, 2017
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	2,237	2,023
Total	2,237	2,023	1,796	2,830
Loans - Ending balance:
Individually evaluated for impairment	1,602	62
Collectively evaluated for impairment	339,710	240,698
Total	341,312	240,760
Non-Covered Loans | Consumer and other
Balance December 31, 2017
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	838	932
Total	838	932	$ 1,432	$ 1,140
Loans - Ending balance:
Individually evaluated for impairment	375	0
Collectively evaluated for impairment	135,534	155,420
Loans, including unearned loan fees	135,909	155,420
Total	$ 137,234	$ 156,182

Portfolio Loans - Summary of 65

Portfolio Loans - Summary of Portfolio Loans Individually Evaluated for Impairment by Category (Details) - Non-Covered Loans - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	$ 24,343	$ 15,057
Recorded Investment With No Allowance	4,856	3,241
Recorded Investment With Allowance	10,831	12,150
Total Recorded Investment	15,687	15,391
Related Allowance	2,579	3,064
Average Recorded Investment	19,722	7,366
Commercial and industrial
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	20,750	12,341
Recorded Investment With No Allowance	2,321	566
Recorded Investment With Allowance	10,344	11,791
Total Recorded Investment	12,665	12,357
Related Allowance	2,508	2,909
Average Recorded Investment	16,270	4,489
CRE - investor owned
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	560	525
Recorded Investment With No Allowance	422	435
Recorded Investment With Allowance	0	0
Total Recorded Investment	422	435
Related Allowance	0	0
Average Recorded Investment	521	668
CRE - owner occupied
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	487	225
Recorded Investment With No Allowance	0	231
Recorded Investment With Allowance	487	0
Total Recorded Investment	487	231
Related Allowance	71	0
Average Recorded Investment	490	227
Construction and land development
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	441	1,904
Recorded Investment With No Allowance	136	1,947
Recorded Investment With Allowance	0	359
Total Recorded Investment	136	2,306
Related Allowance	0	155
Average Recorded Investment	331	1,918
Residential real estate
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	1,730	62
Recorded Investment With No Allowance	1,602	62
Recorded Investment With Allowance	0	0
Total Recorded Investment	1,602	62
Related Allowance	0	0
Average Recorded Investment	1,735	64
Consumer and other
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	375	0
Recorded Investment With No Allowance	375	0
Recorded Investment With Allowance	0	0
Total Recorded Investment	375	0
Related Allowance	0	0
Average Recorded Investment	$ 375	$ 0

Portfolio Loans - Summary of Pa

Portfolio Loans - Summary of Past Due and Impaired Loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Receivables [Abstract]
Total interest income that would have been recognized under original terms on impaired loans	$ 1,324	$ 1,079	$ 1,038
Total cash received and recognized as interest income on impaired loans	643	251	226
Total interest income recognized on impaired loans still accruing	$ 63	$ 155	$ 36

Portfolio Loans - Narrative (De

Portfolio Loans - Narrative (Details) $ in Millions	Dec. 31, 2017USD ($)loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans over 90 days past due and still accruing interest | loan	0
Specific reserves on restructured loans	$ 0
Unadvanced Commitment on Impaired Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Estimated losses attributable to unadvanced commitments on impaired loans	$ 0.4

Portfolio Loans - Summary of 68

Portfolio Loans - Summary of Recorded Investment in Impaired Portfolio Loans by Category (Details) - Non-Covered Loans - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	$ 14,968	$ 13,060
Restructured, not on non-accrual	719	2,331
Total Recorded Investment	15,687	15,391
Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	11,946	10,046
Restructured, not on non-accrual	719	2,311
Total Recorded Investment	12,665	12,357
CRE - investor owned
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	422	435
Restructured, not on non-accrual	0	0
Total Recorded Investment	422	435
CRE - owner occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	487	231
Restructured, not on non-accrual	0	0
Total Recorded Investment	487	231
Construction and land development
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	136	2,286
Restructured, not on non-accrual	0	20
Total Recorded Investment	136	2,306
Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	1,602	62
Restructured, not on non-accrual	0	0
Total Recorded Investment	1,602	62
Consumer and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	375	0
Restructured, not on non-accrual	0	0
Total Recorded Investment	$ 375	$ 0

Portfolio Loans - Summary of 69

Portfolio Loans - Summary of Recorded Investment by Category for Portfolio Loans Restructured (Details) - Non-Covered Loans $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)loan	Dec. 31, 2016USD ($)loan
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	1	7
Pre-Modification Outstanding Recorded Balance	$ 676	$ 12,395
Post-Modification Outstanding Recorded Balance	$ 676	$ 12,395
Commercial and industrial
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	1	4
Pre-Modification Outstanding Recorded Balance	$ 676	$ 12,114
Post-Modification Outstanding Recorded Balance	$ 676	$ 12,114
CRE - investor owned
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	0	1
Pre-Modification Outstanding Recorded Balance	$ 0	$ 248
Post-Modification Outstanding Recorded Balance	$ 0	$ 248
CRE - owner occupied
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	0	1
Pre-Modification Outstanding Recorded Balance	$ 0	$ 13
Post-Modification Outstanding Recorded Balance	$ 0	$ 13
Construction and land development
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	0	1
Pre-Modification Outstanding Recorded Balance	$ 0	$ 20
Post-Modification Outstanding Recorded Balance	$ 0	$ 20
Residential real estate
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	0	0
Pre-Modification Outstanding Recorded Balance	$ 0	$ 0
Post-Modification Outstanding Recorded Balance	$ 0	$ 0
Consumer and other
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	0	0
Pre-Modification Outstanding Recorded Balance	$ 0	$ 0
Post-Modification Outstanding Recorded Balance	$ 0	$ 0

Portfolio Loans - Summary of 70

Portfolio Loans - Summary of Recorded Investment by Category for Portfolio Loans Restructured and Subsequently Defaulted (Details) - Non-Covered Loans $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)loan	Dec. 31, 2016USD ($)loan
Schedule of Financing Receivables, Troubled Debt Restructurings - Suibsequent Defaults [Line Items]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts | loan	3	0
Recorded Balance | $	$ 348	$ 0
Commercial and industrial
Schedule of Financing Receivables, Troubled Debt Restructurings - Suibsequent Defaults [Line Items]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts | loan	2	0
Recorded Balance | $	$ 343	$ 0
Residential Portfolio Segment [Member]
Schedule of Financing Receivables, Troubled Debt Restructurings - Suibsequent Defaults [Line Items]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts | loan	1	0
Recorded Balance | $	$ 5	$ 0

Portfolio Loans - Summary of Ag

Portfolio Loans - Summary of Aging of Recorded Investment in Past Due Portfolio Loans by Portfolio Class and Category (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, including unearned loan fees	$ 4,097,050	$ 3,158,161
Non-Covered Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	10,828	999
Financing Receivable, Recorded Investment, 90 Days Past Due	2,715	2,099
Total Past Due	13,543	3,098
Current	4,009,353	3,115,294
Total	4,024,221	3,119,154
Loans, including unearned loan fees	4,022,896	3,118,392
Non-Covered Loans | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	7,882	334
Financing Receivable, Recorded Investment, 90 Days Past Due	1,770	171
Total Past Due	9,652	505
Current	1,909,068	1,632,209
Total	1,918,720	1,632,714
Non-Covered Loans | CRE - investor owned
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	934	0
Financing Receivable, Recorded Investment, 90 Days Past Due	0	175
Total Past Due	934	175
Current	768,341	544,633
Total	769,275	544,808
Non-Covered Loans | CRE - owner occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	0	212
Financing Receivable, Recorded Investment, 90 Days Past Due	0	225
Total Past Due	0	437
Current	554,589	349,711
Total	554,589	350,148
Non-Covered Loans | Construction and land development
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	76	355
Financing Receivable, Recorded Investment, 90 Days Past Due	0	1,528
Total Past Due	76	1,883
Current	303,015	192,659
Total	303,091	194,542
Non-Covered Loans | Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	1,529	91
Financing Receivable, Recorded Investment, 90 Days Past Due	945	0
Total Past Due	2,474	91
Current	338,838	240,669
Total	341,312	240,760
Non-Covered Loans | Consumer and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	407	7
Financing Receivable, Recorded Investment, 90 Days Past Due	0	0
Total Past Due	407	7
Current	135,502	155,413
Total	137,234	156,182
Loans, including unearned loan fees	$ 135,909	$ 155,420

Portfolio Loans - Summary of 72

Portfolio Loans - Summary of Recorded Investment by Risk Category of Portfolio Loans by Portfolio Class and Category (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans, including unearned loan fees	$ 4,097,050	$ 3,158,161
Non-Covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total	4,024,221	3,119,154
Loans, including unearned loan fees	4,022,896	3,118,392
Non-Covered Loans | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total	1,918,720	1,632,714
Non-Covered Loans | CRE - investor owned
Financing Receivable, Recorded Investment [Line Items]
Total	769,275	544,808
Non-Covered Loans | CRE - owner occupied
Financing Receivable, Recorded Investment [Line Items]
Total	554,589	350,148
Non-Covered Loans | Construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total	303,091	194,542
Non-Covered Loans | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Total	341,312	240,760
Non-Covered Loans | Consumer and other
Financing Receivable, Recorded Investment [Line Items]
Total	137,234	156,182
Loans, including unearned loan fees	135,909	155,420
Pass (1-6) | Non-Covered Loans
Financing Receivable, Recorded Investment [Line Items]
Loans, including unearned loan fees	3,794,940	2,909,234
Pass (1-6) | Non-Covered Loans | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total	1,769,102	1,499,114
Pass (1-6) | Non-Covered Loans | CRE - investor owned
Financing Receivable, Recorded Investment [Line Items]
Total	514,616	306,658
Pass (1-6) | Non-Covered Loans | CRE - owner occupied
Financing Receivable, Recorded Investment [Line Items]
Total	754,010	530,494
Pass (1-6) | Non-Covered Loans | Construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total	292,766	185,505
Pass (1-6) | Non-Covered Loans | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Total	329,742	233,479
Pass (1-6) | Non-Covered Loans | Consumer and other
Financing Receivable, Recorded Investment [Line Items]
Loans, including unearned loan fees	134,704	153,984
Watch (7) | Non-Covered Loans
Financing Receivable, Recorded Investment [Line Items]
Loans, including unearned loan fees	152,923	116,686
Watch (7) | Non-Covered Loans | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total	94,002	57,416
Watch (7) | Non-Covered Loans | CRE - investor owned
Financing Receivable, Recorded Investment [Line Items]
Total	34,440	39,249
Watch (7) | Non-Covered Loans | CRE - owner occupied
Financing Receivable, Recorded Investment [Line Items]
Total	10,840	10,449
Watch (7) | Non-Covered Loans | Construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total	9,983	6,575
Watch (7) | Non-Covered Loans | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Total	3,648	2,997
Watch (7) | Non-Covered Loans | Consumer and other
Financing Receivable, Recorded Investment [Line Items]
Loans, including unearned loan fees	10	0
Substandard (8) | Non-Covered Loans
Financing Receivable, Recorded Investment [Line Items]
Loans, including unearned loan fees	75,033	92,472
Substandard (8) | Non-Covered Loans | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total	55,616	76,184
Substandard (8) | Non-Covered Loans | CRE - investor owned
Financing Receivable, Recorded Investment [Line Items]
Total	5,533	4,241
Substandard (8) | Non-Covered Loans | CRE - owner occupied
Financing Receivable, Recorded Investment [Line Items]
Total	4,425	3,865
Substandard (8) | Non-Covered Loans | Construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total	342	2,462
Substandard (8) | Non-Covered Loans | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Total	7,922	4,284
Substandard (8) | Non-Covered Loans | Consumer and other
Financing Receivable, Recorded Investment [Line Items]
Loans, including unearned loan fees	$ 1,195	$ 1,436

Purchased Credit Impaired ("P73

Purchased Credit Impaired ("PCI") Loans - Summary of PCI Loans by Category (Details) - Covered Loans $ in Thousands	Dec. 31, 2017USD ($)rating	Dec. 31, 2016USD ($)rating
Covered Loans [Line Items]
Recorded Investment PCI Loans	$ 74,154	$ 39,769
Commercial and industrial
Covered Loans [Line Items]
Weighted- Average Risk Rating1 | rating	6.38	5.87
Recorded Investment PCI Loans	$ 3,212	$ 3,523
CRE - investor owned
Covered Loans [Line Items]
Weighted- Average Risk Rating1 | rating	7.36	6.95
Recorded Investment PCI Loans	$ 42,887	$ 8,162
CRE - owner occupied
Covered Loans [Line Items]
Weighted- Average Risk Rating1 | rating	6.48	6.39
Recorded Investment PCI Loans	$ 11,332	$ 11,863
Construction and land development
Covered Loans [Line Items]
Weighted- Average Risk Rating1 | rating	5.99	5.80
Recorded Investment PCI Loans	$ 5,883	$ 4,365
Residential real estate
Covered Loans [Line Items]
Weighted- Average Risk Rating1 | rating	5.99	5.64
Recorded Investment PCI Loans	$ 10,781	$ 11,792
Total real estate loans
Covered Loans [Line Items]
Recorded Investment PCI Loans	$ 70,883	$ 36,182
Consumer and other
Covered Loans [Line Items]
Weighted- Average Risk Rating1 | rating	2.84	1.64
Recorded Investment PCI Loans	$ 59	$ 64

Purchased Credit Impaired ("P74

Purchased Credit Impaired ("PCI") Loans - Summary of Aging of Recorded Investment in Past Due PCI Loans by Portfolio Class and Category (Details) - Covered Loans - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	$ 328	$ 169
90 or More Days Past Due	3,962	51
Total Past Due	4,290	220
Current	69,864	39,549
Total	74,154	39,769
Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	0	0
90 or More Days Past Due	0	0
Total Past Due	0	0
Current	3,212	3,523
Total	3,212	3,523
CRE - investor owned
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	0	0
90 or More Days Past Due	3,034	0
Total Past Due	3,034	0
Current	39,853	8,162
Total	42,887	8,162
CRE - owner occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	0	0
90 or More Days Past Due	673	0
Total Past Due	673	0
Current	10,659	11,863
Total	11,332	11,863
Construction and land development
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	0	0
90 or More Days Past Due	0	0
Total Past Due	0	0
Current	5,883	4,365
Total	5,883	4,365
Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	328	169
90 or More Days Past Due	255	51
Total Past Due	583	220
Current	10,198	11,572
Total	10,781	11,792
Consumer and other
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 Days Past Due	0	0
90 or More Days Past Due	0	0
Total Past Due	0	0
Current	59	64
Total	$ 59	$ 64

Purchased Credit Impaired ("P75

Purchased Credit Impaired ("PCI") Loans - Rollforward of PCI Loans, Net of Allowance for Loan Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	$ 33,925	$ 64,583
Principal reductions and interest payments	(24,530)	(25,669)
Acquisitions	(49,155)
Accretion of loan discount	7,573	6,155
Changes in contractual and expected cash flows due to remeasurement	(9,957)	(12,452)
Reductions due to disposals	(6,337)	(23,596)
Balance at end of period	69,743	33,925
Contractual Cashflows
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	66,003	116,689
Principal reductions and interest payments	(24,530)	(25,669)
Acquisitions	(68,763)
Accretion of loan discount	0	0
Changes in contractual and expected cash flows due to remeasurement	(13,978)	(11,718)
Reductions due to disposals	(11,503)	(36,735)
Balance at end of period	112,711	66,003
Non-accretable Difference
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	18,902	26,765
Principal reductions and interest payments	0	0
Acquisitions	(14,296)
Accretion of loan discount	0	0
Changes in contractual and expected cash flows due to remeasurement	(1,465)	(766)
Reductions due to disposals	(2,727)	(8,629)
Balance at end of period	29,006	18,902
Accretable Yield
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	13,176	25,341
Principal reductions and interest payments	0	0
Acquisitions	(5,312)
Accretion of loan discount	7,573	6,155
Changes in contractual and expected cash flows due to remeasurement	(5,486)	(1,500)
Reductions due to disposals	(2,439)	(4,510)
Balance at end of period	$ 13,962	$ 13,176

Purchased Credit Impaired ("P76

Purchased Credit Impaired ("PCI") Loans - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016
Receivables [Abstract]
PCI loans outstanding		$ 94.9	$ 54.6
Net payment received from FDIC for loss share termination	$ 1.3
Removal of remaining clawback liability, FDIC loss share termination	3.5
Removal of remaining FDIC receivable, FDIC loss share termination	7.2
One-time pretax charge	$ 2.4

Derivative Financial Instrume77

Derivative Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Derivative Liability, Notional Amount		$ 3,500
Pledged cash as collateral in connection with interest rate swap agreements	$ 1,400	700
Non-designated hedging instruments | Client-Related | Interest rate swap contracts
Summary of Derivative Instruments [Abstract]
Notional Amount	394,852	124,322
Non-designated hedging instruments | Client-Related | Foreign Exchange Forward [Member]
Summary of Derivative Instruments [Abstract]
Notional Amount	1,528	3,034
Non-designated hedging instruments | Client-Related | Other Assets | Interest rate swap contracts
Derivative [Line Items]
Unrealized Gain Derivative Instruments	2,061
Summary of Derivative Instruments [Abstract]
Derivative Asset, Fair Value, Gross Asset	2,061	982
Non-designated hedging instruments | Client-Related | Other Assets | Foreign Exchange Forward [Member]
Summary of Derivative Instruments [Abstract]
Derivative Asset, Fair Value, Gross Asset	1,528	3,034
Non-designated hedging instruments | Client-Related | Other Liabilities | Interest rate swap contracts
Summary of Derivative Instruments [Abstract]
Liability derivatives (other liabilities), fair value	2,061	982
Non-designated hedging instruments | Client-Related | Other Liabilities | Foreign Exchange Forward [Member]
Summary of Derivative Instruments [Abstract]
Liability derivatives (other liabilities), fair value	$ 1,528	$ 3,034

Fixed Assets - Summary of Fixed

Fixed Assets - Summary of Fixed Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Land	$ 7,263	$ 3,103
Buildings and leasehold improvements	32,384	18,054
Furniture, fixtures and equipment	8,272	6,136
Capitalized software	1,305	1,305
Fixed assets, gross	49,224	28,598
Less accumulated depreciation and amortization	16,606	13,688
Fixed assets, net	$ 32,618	$ 14,910

Fixed Assets - Narrative (Detai

Fixed Assets - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Lease Abandonment Expense	$ 0.4	$ 0.5	$ 0.1
Depreciation and amortization	3.3	2.4	2
Rent expense	3.3	3.1	3.1
Sublease rental income	0	$ 0.1	$ 0.1
Discontinued Operations, Disposed of by Means Other than Sale, Abandonment [Member]
Lease Abandonment Liability	$ 2

Fixed Assets - Future Aggregate

Fixed Assets - Future Aggregate Minimum Rental Commitments (Details) $ in Thousands	Dec. 31, 2017USD ($)
Future Aggregate Minimum Rental Commitments
2,017	$ 3,503
2,018	3,477
2,019	3,418
2,020	3,337
2,021	2,801
Thereafter	5,962
Total	$ 22,498

Goodwill and Intangible Asset81

Goodwill and Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	$ 30,334	$ 30,334
Amortization of intangible assets	$ 2,609	$ 924	$ 1,089
Finite-lived intangible assets useful life	10 years	10 years
Finite-Lived Intangible Assets [Line Items]
Core deposit intangible, net, end of year	$ 11,056
Core Deposits [Member]
Goodwill and Intangible Assets Disclosure [Abstract]
Finite-lived intangible assets useful life	10 years
Finite-Lived Intangible Assets [Line Items]
Gross core deposit intangible balance, beginning of year	$ 20,574	$ 9,060	$ 9,060
Acquired Finite-lived Intangible Asset, Residual Value	11,514	0
Accumulated amortization	(9,518)	(6,909)
Core deposit intangible, net, end of year	$ 11,056	$ 2,151

Goodwill and Intangible Asset82

Goodwill and Intangible Assets - Expected Amortization Schedule for the Core Deposit Intangible (Details) $ in Thousands	Dec. 31, 2017USD ($)
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
2,015	$ 2,504
2,016	2,129
2,017	1,755
2,018	1,381
2,019	1,071
After 2,022	2,216
Core deposit intangible, net, end of year	$ 11,056

Maturity of Certificates of D83

Maturity of Certificates of Deposit (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Brokered
Less than 1 year	$ 114,054
Greater than 1 year and less than 2 years	1,252
Greater than 2 years and less than 3 years	0
Greater than 3 years and less than 4 years	0
Greater than 4 years and less than 5 years	0
Greater than 5 years	0
Brokered	115,306	$ 117,145
Customer
Less than 1 year	317,373
Greater than 1 year and less than 2 years	74,236
Greater than 2 years and less than 3 years	48,553
Greater than 3 years and less than 4 years	21,100
Greater than 4 years and less than 5 years	1,598
Greater than 5 years	607
Other	463,467	$ 356,014
Total
Less than 1 year	431,427
Greater than 1 year and less than 2 years	75,488
Greater than 2 years and less than 3 years	48,553
Greater than 3 years and less than 4 years	21,100
Greater than 4 years and less than 5 years	1,598
Greater than 5 years	607
Total Time Deposits	578,773
Time Deposits, $250,000 or More	$ 148,000

Subordinated Debentures (Detail

Subordinated Debentures (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)shares	Dec. 31, 2016USD ($)shares	Dec. 31, 2015shares	Nov. 01, 2021	Nov. 01, 2016USD ($)
Subordinated Borrowing [Line Items]
Number of Unconsolidated Statutory Business Trusts	10
Investments trust preferred securities	$ 2,100
Subordinated debentures and notes (net of debt issuance cost of $1,136 and $1,267, respectively)	118,105	$ 105,540
Debt issuance costs	$ (1,136)	$ (1,267)
Conversion of subordinated debt into common stock (in shares) | shares	0	0	0
Senior Subordinated Notes [Member]
Subordinated Borrowing [Line Items]
Senior Subordinated Notes					$ 50,000
Subordinated Notes, Redemption Price				100.00%
Trust preferred securities [Member]
Subordinated Borrowing [Line Items]
Subordinated debentures and notes (net of debt issuance cost of $1,136 and $1,267, respectively)	$ 69,241	$ 56,807
Trust preferred securities [Member] | EFSC Clayco Statutory Trust I
Subordinated Borrowing [Line Items]
Subordinated debentures and notes (net of debt issuance cost of $1,136 and $1,267, respectively)	$ 3,196	3,196
Maturity Date	Dec. 17, 2033
Call Date	Dec. 17, 2008
Description of variable rate	3 Month LIBOR
Floating interest rate	2.85%
Trust preferred securities [Member] | EFSC Capital Trust II
Subordinated Borrowing [Line Items]
Subordinated debentures and notes (net of debt issuance cost of $1,136 and $1,267, respectively)	$ 5,155	5,155
Maturity Date	Jun. 17, 2034
Call Date	Jun. 17, 2009
Description of variable rate	3 Month LIBOR
Floating interest rate	2.65%
Trust preferred securities [Member] | EFSC Statutory Trust III
Subordinated Borrowing [Line Items]
Subordinated debentures and notes (net of debt issuance cost of $1,136 and $1,267, respectively)	$ 11,341	11,341
Maturity Date	Dec. 15, 2034
Call Date	Dec. 15, 2009
Description of variable rate	3 Month LIBOR
Floating interest rate	1.97%
Trust preferred securities [Member] | EFSC Clayco Statutory Trust II
Subordinated Borrowing [Line Items]
Subordinated debentures and notes (net of debt issuance cost of $1,136 and $1,267, respectively)	$ 4,124	4,124
Maturity Date	Sep. 15, 2035
Call Date	Sep. 15, 2010
Description of variable rate	3 Month LIBOR
Floating interest rate	1.83%
Trust preferred securities [Member] | EFSC Statutory Trust IV
Subordinated Borrowing [Line Items]
Subordinated debentures and notes (net of debt issuance cost of $1,136 and $1,267, respectively)	$ 10,310	10,310
Maturity Date	Dec. 15, 2035
Call Date	Dec. 15, 2010
Description of variable rate	3 Month LIBOR
Floating interest rate	1.44%
Trust preferred securities [Member] | EFSC Statutory Trust V
Subordinated Borrowing [Line Items]
Subordinated debentures and notes (net of debt issuance cost of $1,136 and $1,267, respectively)	$ 4,124	4,124
Maturity Date	Sep. 15, 2036
Call Date	Sep. 15, 2011
Description of variable rate	3 Month LIBOR
Floating interest rate	1.60%
Trust preferred securities [Member] | EFSC Capital Trust VI
Subordinated Borrowing [Line Items]
Subordinated debentures and notes (net of debt issuance cost of $1,136 and $1,267, respectively)	$ 14,433	14,433
Maturity Date	Mar. 30, 2037
Call Date	Mar. 30, 2012
Description of variable rate	3 Month LIBOR
Floating interest rate	1.60%
Trust preferred securities [Member] | EFSC Capital Trust VII
Subordinated Borrowing [Line Items]
Subordinated debentures and notes (net of debt issuance cost of $1,136 and $1,267, respectively)	$ 4,124	4,124
Maturity Date	Dec. 15, 2037
Call Date	Dec. 15, 2012
Description of variable rate	3 Month LIBOR
Floating interest rate	2.25%
Trust preferred securities [Member] | JEFFCO Stat Trust I [Member]
Subordinated Borrowing [Line Items]
Subordinated debentures and notes (net of debt issuance cost of $1,136 and $1,267, respectively)	$ 8,153	0
Maturity Date	Feb. 22, 2031
Call Date	Feb. 22, 2011
Fixed interest rate	10.20%
Trust preferred securities [Member] | EFSC Capital Trust VIII
Subordinated Borrowing [Line Items]
Fixed interest rate	9.00%
Trust preferred securities [Member] | JEFFCO Stat Trust II [Member]
Subordinated Borrowing [Line Items]
Subordinated debentures and notes (net of debt issuance cost of $1,136 and $1,267, respectively)	$ 4,281	0
Maturity Date	Mar. 17, 2034
Call Date	Mar. 17, 2009
Description of variable rate	3 Month LIBOR
Fixed interest rate	2.75%
Senior Subordinated Notes [Member]
Subordinated Borrowing [Line Items]
Subordinated debentures and notes (net of debt issuance cost of $1,136 and $1,267, respectively)	$ 50,000	50,000
Debt issuance costs	(1,136)	(1,267)
Subordinated notes, net of issuance costs	$ 48,864	$ 48,733
Maturity Date	Nov. 1, 2026
Call Date	Nov. 1, 2021
Floating interest rate	3.387%
Fixed interest rate	4.75%

Federal Home Loan Bank Advanc85

Federal Home Loan Bank Advances (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Federal Home Loan Bank, Advances, Branch of FHLB [Line Items]
Carrying value of the loans pledged	$ 172,743	$ 0
Short term advances outstanding	$ 172,743	$ 0
Weighted average interest rate on short term advances	2.00%	0.00%
Collateral used to secure confirming letters of credit	$ 18,100
Weighted Rate
Federal Home Loan Bank, Advances, Maturities Summary, One to Five Years	$ 0	$ 0
Federal Home Loan Bank Advances, Maturities Summary, Average Interest Rate of Amounts Due in One to Five Years of Balance Sheet Date	0.00%	0.00%
Federal Home Loan Bank, Advances, Maturities Summary, Average Interst Rate of Amounts	2.00%	0.00%
Des Moines
Federal Home Loan Bank, Advances, Branch of FHLB [Line Items]
Carrying value of the loans pledged	$ 1,144,400	$ 773,500
Availability under the secured line of credit	484,700
Investment in capital stock	$ 12,900

Other Borrowings and Notes Pa86

Other Borrowings and Notes Payable (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Feb. 23, 2016
Debt Instrument [Line Items]
Line of Credit, Current			$ 20,000,000
Securities sold under customer repurchase agreements	$ 253,674,000	$ 276,980,000
Total	253,674,000	276,980,000
Amount withdrawn	0	0
Other Borrowings
Debt Instrument [Line Items]
Maximum balance outstanding at any month-end	253,674,000	276,980,000
Average balance during the year	$ 220,807,000	$ 206,643,000
Average interest rate during the year	0.21%	0.19%
Average interest rate at December 31	0.25%	0.18%
Line of Credit
Debt Instrument [Line Items]
Maximum balance outstanding at any month-end	$ 10,000,000	$ 0
Average balance during the year	$ 822,000	$ 0
Average interest rate during the year	3.50%	0.00%
Average interest rate at December 31	0.00%	0.00%
Remaining borrowing capacity	$ 898,100,000
Aggregate of pledge secured by certain eligible loans	1,071,600,000
Amount withdrawn	$ 0

Regulatory Matters (Details)

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%

Compensation Plans - Narrative

Compensation Plans - Narrative (Details) - USD ($) $ in Thousands	1 Months Ended			12 Months Ended
	Jan. 31, 2018	Feb. 28, 2017	Jan. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant				86,082
Share-based compensation expense				$ 3,400	$ 3,400	$ 3,600
Tax benefit from compensation expense				$ 2,100	1,300	$ 400
Award vesting period						3 years
Number of shares issued upon completion of performance cycle		118,519	159,094
Employee minimum age to participate in plan				21 years
Company contributions, amount charged to expense				$ 2,000	$ 1,700	$ 1,600
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term					10 years
Stock Appreciation Rights (SSARs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period				5 years
Contractual term				10 years
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense				$ 898	$ 850	725
Total unrecognized compensation cost (less than)				$ 837	1,084	942
Number of shares issued				16,462
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense				$ 100	0	$ 200
Number of shares issued				0		14,110
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense				$ 2,500	2,500	$ 2,700
Share-based compensation expense, retiring executive				$ 300	200
Award vesting period						3 years
Minimum | Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period				3 years
Minimum | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period				2 years
Minimum | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period				2 years
Maximum | Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period				5 years
Maximum | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period				5 years
Maximum | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period				5 years
Stock Plan for Non-Management Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant				19,163
Share-based compensation expense				$ 397	$ 407	$ 373
Number of shares authorized				200,000
Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued upon completion of performance cycle	134,600

Compensation Plans - Schedule o

Compensation Plans - Schedule of Various Information (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	$ 3,400	$ 3,400	$ 3,600
Weighted average fair value (usd per share)	$ 40,720	$ 25,260
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	$ 898	$ 850	725
Total fair value at vesting date	1,471	2,275	809
Total unrecognized compensation cost for nonvested stock units	$ 837	$ 1,084	$ 942
Expected years to recognize unearned compensation	1 year 9 months	1 year 7 months	1 year 8 months
Stock Options and SSARs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	$ 0	$ 0	$ 50
Intrinsic value of option exercises on date of exercise	3,156	1,156	74
Cash received from the exercise of stock options	91	87	126
Stock Plan for Non-Management Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	$ 397	$ 407	$ 373
Number of shares issued	10,531,000	12,528,000	16,283,000
Weighted average fair value (usd per share)	$ 42.46	$ 31.25	$ 24.43

Compensation Plans - Schedule90

Compensation Plans - Schedule of Employee Stock Options and SSARs Activity (Details) - Stock Options and SSARs	12 Months Ended
	Dec. 31, 2017USD ($)$ / sharesshares
Shares
Outstanding at beginning of period (in shares) | shares	270,246
Granted (in shares) | shares	0
Exercised (in shares) | shares	(164,116)
Forfeited (in shares) | shares	0
Outstanding at end of period (in shares) | shares	106,130
Exercisable (in shares) | shares	106,130
Weighted Average Exercise Price
Outstanding at beginning of period (usd per share) | $ / shares	$ 18.85
Granted (usd per share) | $ / shares	0
Exercised (usd per share) | $ / shares	22.40
Forfeited (usd per share) | $ / shares	0
Outstanding at end of period (usd per share) | $ / shares	13.37
Exercisable (usd per share) | $ / shares	$ 13.37
Additional Disclosures
Outstanding, weighted average remaining contractual term	1 year 11 months
Exercisable, weighted average remaining contractual term	1 year 11 months
Outstanding, aggregate intrinsic value | $	$ 3,373
Exercisable, aggregate intrinsic value | $	$ 3,373

Compensation Plans - Summary of

Compensation Plans - Summary of Restricted Stock Units Activity (Details) - Restricted Stock Units (RSUs)	12 Months Ended
	Dec. 31, 2017$ / sharesshares
Shares
Outstanding, beginning of period (in shares) | shares	58,698
Granted (in shares) | shares	16,462
Vested (in shares) | shares	(33,206)
Forfeited (in shares) | shares	(732)
Outstanding, end of period (in shares) | shares	41,222
Weighted Average Grant Date Fair Value
Outstanding, beginning of period (usd per share) | $ / shares	$ 23.06
Granted (usd per share) | $ / shares	41.68
Vested (usd per share) | $ / shares	18.48
Forfeited (usd per share) | $ / shares	14.48
Outstanding, end of period (usd per share) | $ / shares	$ 34.34

Compensation Plans Outstanding

Compensation Plans Outstanding Longer Term Incentive Awards (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Outstanding Long Term Incentive Awards [Line Items]
Target Shares Issuable as Long Term Incentive Awards	$ 55,203	$ 87,758
Maximum Shares Issuable as Long Term Incentive Awards	68,263	107,955
Unrecognized Compensation Cost - Long Term Incentives	$ 1,792,393	$ 949,095
Share-based Compensation Arrangement By Share-based Payment Award, Grants In Period, Weighted Average Grant Date Fair Value	$ 40,720	$ 25,260

Income Taxes - Schedule of Comp

Income Taxes - Schedule of Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Examination [Line Items]
Federal									$ 15,845	$ 17,005	$ 22,916
State and local									1,377	1,734	2,798
Current Federal, State and Local, Tax Expense (Benefit)									17,222	18,739	25,714
Deferred:									21,105	7,263	(5,763)
Deferred Federal Income Tax Expense (Benefit)									20,989	5,959	(5,266)
Deferred State and Local Income Tax Expense (Benefit)									116	1,304	(497)
Deferred Federal, State and Local, Tax Expense (Benefit)									21,105	7,263	(5,763)
Total income tax expense	$ 19,820	$ 7,856	$ 5,545	$ 5,106	$ 7,053	$ 6,316	$ 6,747	$ 5,886	$ 38,327	$ 26,002	$ 19,951

Income Taxes - Schedule of Inco

Income Taxes - Schedule of Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Increase (reduction) in income tax resulting from:
Income tax expense at statutory rate									$ 30,281	$ 26,194	$ 20,440
Tax-exempt income, net									(961)	(945)	(931)
State and local income taxes, net									1,676	1,673	1,414
Bank-owned life insurance, net									(715)	(544)	(462)
Non-deductible expenses									407	263	259
Change in estimated rate for deferred taxes									12,117	302	0
Tax benefits of LIHTC investments, net									(257)	(181)	(179)
Other, net									(379)	(760)	(590)
Effective Income Tax Rate Reconciliation, Tax Credit, Amount									(2,141)	0	0
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Amount									(1,701)	0	0
Total income tax expense	$ 19,820	$ 7,856	$ 5,545	$ 5,106	$ 7,053	$ 6,316	$ 6,747	$ 5,886	$ 38,327	$ 26,002	$ 19,951

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets and Deferred Tax Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Deferred Tax [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	24.70%	38.00%	35.00%	35.00%
Deferred tax assets:
Allowance for loan losses	$ 10,516	$ 16,496
Basis difference on PCI assets, net	5,748	5,551
Basis difference on Other real estate	694	317
Deferred compensation	2,719	4,217
Goodwill and other intangible assets	2,151	5,520
Accrued compensation	646	899
Unrealized losses on securities available for sale	1,490	1,019
Other, net	2,150	925
Total deferred tax assets	26,114	34,944
Deferred Tax Liabilities, Other	855	0
Deferred tax liabilities:
State tax credits held for sale, net of economic hedge	26	376
Core deposit intangibles	2,731	817
Total deferred tax liabilities	3,612	1,193
Deferred Tax Assets, Net	22,502	33,751
Other Assets
Deferred tax liabilities:
Deferred Tax Assets, Net	$ 22,500	$ 33,800

Income Taxes - Schedule of Unre

Income Taxes - Schedule of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
Balance at beginning of year	$ 1,180	$ 1,359	$ 1,884
Additions based on tax positions related to the current year	331	239	230
Additions for tax positions of prior years	41	39	46
Reductions for tax positions of prior years	0	0	(437)
Settlements or lapse of statute of limitations	(308)	(457)	(364)
Balance at end of year	$ 1,244	$ 1,180	$ 1,359

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details)	12 Months Ended
	Dec. 31, 2017USD ($)state	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Feb. 10, 2017USD ($)
Income Tax Disclosure [Abstract]
Statutory federal income tax rate	24.70%	38.00%	35.00%	35.00%
Income Tax Examination [Line Items]
Income Tax Reconciliation Enacted Tax Rate Change	$ 12,100,000
Tax credits and other tax benefits from low-income housing tax credit			$ 1,100,000	$ 1,100,000
Amount recognized as a component of income tax expense related low-income housing tax credit	300,000	$ 200,000	200,000
Investments related to low-income housing tax credits	1,300,000	1,400,000
Impairment losses recognized from forfeiture or ineligibility	0		0	0
Future capital commitments related to low-income housing tax credit investments	4,800,000
Deferred Tax Assets, Net	$ 22,502,000	33,751,000
Number of states the company files income tax returns in | state	9
Unrecognized tax benefits	$ 1,244,000	1,180,000	1,359,000	$ 1,884,000
Unrecognized tax benefits that would impact effective tax rate	800,000	800,000	900,000
Reduction in unrecognized tax benefit that is reasonably possible due to a lapse of statute of limitations	$ 300,000
Duration of unrecognized tax benefits	12 months
State and Local Jurisdiction [Member]
Income Tax Examination [Line Items]
State valuation allowance			$ 0
Other Assets
Income Tax Examination [Line Items]
Deferred Tax Assets, Net	$ 22,500,000	$ 33,800,000
As Recorded by EFSC [Member]
Income Tax Examination [Line Items]
Deferred Tax Assets, State Taxes	$ 8,600,000				$ 8,625,000

Commitments (Details)

Commitments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Commitments to extend credit
Schedule of Commitments [Line Items]
Off-balance sheet financial instruments, contractual amounts	$ 1,298,423	$ 1,075,170
Letters of credit
Schedule of Commitments [Line Items]
Off-balance sheet financial instruments, contractual amounts	$ 73,790	78,954
Letters of credit | Minimum
Schedule of Commitments [Line Items]
Remaining term	1 month
Letters of credit | Maximum
Schedule of Commitments [Line Items]
Remaining term	3 years 9 months
Unadvanced Commitment on Impaired Loan
Schedule of Commitments [Line Items]
Estimated losses attributable to unadvanced commitments on impaired loans	$ 400
Fixed Rate Loan Commitment | Commitments to extend credit
Schedule of Commitments [Line Items]
Off-balance sheet financial instruments, contractual amounts	$ 112,000	$ 89,700

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Instruments Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets
Securities available for sale	$ 641,382	$ 460,797
State tax credits held for sale	400
Portion at Other than Fair Value, Fair Value Disclosure
Assets
State tax credits held for sale	43,100
Total Fair Value
Assets
Securities available for sale	641,382	460,797
State tax credits held for sale	44,271	41,264
Derivative financial instruments	3,589	4,016
Liabilities
Derivative financial instruments	3,589	4,016
Obligations of U.S. Government-sponsored enterprises
Assets
Securities available for sale	99,224	107,660
Obligations of states and political subdivisions
Assets
Securities available for sale	34,642	36,631
Residential mortgage-backed securities
Assets
Securities available for sale	507,516	316,506
Recurring basis | Total Fair Value
Assets
Securities available for sale	641,382	460,797
State tax credits held for sale	400	3,585
Derivative financial instruments	3,589	4,016
Assets, Fair Value Disclosure	645,371	468,398
Liabilities
Derivative financial instruments	3,589	4,016
Total liabilities	3,589	4,016
Recurring basis | Obligations of U.S. Government-sponsored enterprises | Total Fair Value
Assets
Securities available for sale	99,224	107,660
Recurring basis | Obligations of states and political subdivisions | Total Fair Value
Assets
Securities available for sale	34,642	36,631
Recurring basis | Residential mortgage-backed securities | Total Fair Value
Assets
Securities available for sale	507,516	316,506
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Securities available for sale	0	0
State tax credits held for sale	0	0
Derivative financial instruments	0	0
Assets, Fair Value Disclosure	0	0
Liabilities
Derivative financial instruments	0	0
Total liabilities	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Obligations of U.S. Government-sponsored enterprises
Assets
Securities available for sale	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Obligations of states and political subdivisions
Assets
Securities available for sale	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Residential mortgage-backed securities
Assets
Securities available for sale	0	0
Recurring basis | Significant Other Observable Inputs (Level 2)
Assets
Securities available for sale	641,382	457,708
State tax credits held for sale	0	0
Derivative financial instruments	3,589	4,016
Assets, Fair Value Disclosure	644,971	461,724
Liabilities
Derivative financial instruments	3,589	4,016
Total liabilities	3,589	4,016
Recurring basis | Significant Other Observable Inputs (Level 2) | Obligations of U.S. Government-sponsored enterprises
Assets
Securities available for sale	99,224	107,660
Recurring basis | Significant Other Observable Inputs (Level 2) | Obligations of states and political subdivisions
Assets
Securities available for sale	34,642	33,542
Recurring basis | Significant Other Observable Inputs (Level 2) | Residential mortgage-backed securities
Assets
Securities available for sale	507,516	316,506
Recurring basis | Significant Unobservable Inputs (Level 3)
Assets
Securities available for sale	0	3,089
State tax credits held for sale	400	3,585
Derivative financial instruments	0	0
Assets, Fair Value Disclosure	400	6,674
Liabilities
Derivative financial instruments	0	0
Total liabilities	0	0
Recurring basis | Significant Unobservable Inputs (Level 3) | Obligations of U.S. Government-sponsored enterprises
Assets
Securities available for sale	0	0
Recurring basis | Significant Unobservable Inputs (Level 3) | Obligations of states and political subdivisions
Assets
Securities available for sale	0	3,089
Recurring basis | Significant Unobservable Inputs (Level 3) | Residential mortgage-backed securities
Assets
Securities available for sale	$ 0	$ 0

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)security	Dec. 31, 2016USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
State tax credits, held for sale, including $400 and $3,585 carried at fair value, respectively	$ 43,468	$ 38,071
State Tax Credits Held For Sale, Fair Value Disclosure	$ 400
State tax credit term	10 years
Years of tax credits generated	10 years
Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
State tax credits, held for sale, including $400 and $3,585 carried at fair value, respectively	$ 43,500
Recurring basis | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
State Tax Credits Held For Sale, Fair Value Disclosure	$ 400	3,585
Auction Rate Securities | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of available-for-sale securities | security	0
Portion at Other than Fair Value, Fair Value Disclosure
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
State Tax Credits Held For Sale, Fair Value Disclosure	$ 43,100
Estimated fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
State Tax Credits Held For Sale, Fair Value Disclosure	44,271	41,264
Estimated fair value | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
State Tax Credits Held For Sale, Fair Value Disclosure	400	3,585
State tax credits held for sale, at fair value | Recurring basis | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in unrealized (losses) gains relating to assets still held at the reporting date	$ (885)	$ 575
Minimum | State tax credits held for sale, at fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	2.30%
Maximum | State tax credits held for sale, at fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	4.82%
LIBOR | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate basis spread on variable rate	285.00%
LIBOR | LIBOR Swap Curve
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate basis point spread	2.05
Discount rate basis spread on variable rate	205.00%	205.00%
LIBOR | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate basis spread on variable rate	265.00%
Prime Rate | State tax credits held for sale, at fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate basis spread on variable rate	75.00%

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Level 3 Financial Instruments Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	$ 641,382	$ 460,797
Held-to-maturity Securities, Fair Value	73,458	79,639
Level 3 | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0	3,089
Level 3 | Securities available for sale, at fair value | Recurring basis
Level 3 Financial Instruments Measured at Fair Value
Beginning balance	3,089	3,077
Total gains:
Included in other comprehensive income	4	12
Purchases, sales, issuances and settlements
Transfer in and/or out of Level 3		(3,093)	$ 0
Ending balance	0	3,089	3,077
Change in unrealized gains relating to assets still held at the reporting date	0	12
Level 3 | State tax credits held for sale, at fair value | Recurring basis
Level 3 Financial Instruments Measured at Fair Value
Beginning balance	3,585	5,941
Total gains:
Total gains:	101	177
Purchases, sales, issuances and settlements
Sales	(3,286)	(2,533)
Ending balance	400	3,585	$ 5,941
Change in unrealized gains relating to assets still held at the reporting date	885	(575)
Quoted Prices in Active Markets for Identical Assets (Level 1) | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0	0
Significant Other Observable Inputs (Level 2) | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	641,382	457,708
Total Fair Value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	641,382	460,797
Total Fair Value | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	641,382	460,797
Obligations of U.S. Government-sponsored enterprises
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	99,224	107,660
Obligations of U.S. Government-sponsored enterprises | Level 3 | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0	0
Obligations of U.S. Government-sponsored enterprises | Quoted Prices in Active Markets for Identical Assets (Level 1) | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0	0
Obligations of U.S. Government-sponsored enterprises | Significant Other Observable Inputs (Level 2) | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	99,224	107,660
Obligations of U.S. Government-sponsored enterprises | Total Fair Value | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	99,224	107,660
Obligations of states and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	34,642	36,631
Obligations of states and political subdivisions | Level 3 | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0	3,089
Obligations of states and political subdivisions | Quoted Prices in Active Markets for Identical Assets (Level 1) | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0	0
Obligations of states and political subdivisions | Significant Other Observable Inputs (Level 2) | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	34,642	33,542
Obligations of states and political subdivisions | Total Fair Value | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	34,642	36,631
Residential mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	507,516	316,506
Residential mortgage-backed securities | Level 3 | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0	0
Residential mortgage-backed securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	0	0
Residential mortgage-backed securities | Significant Other Observable Inputs (Level 2) | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	507,516	316,506
Residential mortgage-backed securities | Total Fair Value | Recurring basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value	$ 507,516	$ 316,506

Fair Value Measurements - Su102

Fair Value Measurements - Summary of Financial Instruments and Non-Financial Assets Measured at Fair Value on a Non-Recurring Basis (Details) - Fair Value, Measurements, Nonrecurring - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total (losses) gains for the year	$ 6,599	$ 4,336
Impaired loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total (losses) gains for the year	6,599	4,335
Other real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total (losses) gains for the year	0	1
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Impaired loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other real estate	0	0
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
Significant Other Observable Inputs (Level 2) | Impaired loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	0	0
Significant Other Observable Inputs (Level 2) | Other real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other real estate	0	0
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	3,200	175
Significant Unobservable Inputs (Level 3) | Impaired loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	3,200	175
Significant Unobservable Inputs (Level 3) | Other real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other real estate	0	0
Total Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	3,200	175
Total Fair Value | Impaired loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	3,200	175
Total Fair Value | Other real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other real estate	$ 0	$ 0

Fair Value Measurements - Su103

Fair Value Measurements - Summary of Carrying Amount and Fair Values of Financial Instruments Reported on the Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Balance sheet assets
Securities available for sale	$ 641,382	$ 460,797
Securities held to maturity	73,749	80,463
State tax credits held for sale	400
Carrying Amount
Balance sheet assets
Cash and due from banks	91,084	54,288
Federal funds sold	1,223	446
Interest-bearing deposits	63,661	145,048
Securities available for sale	641,382	460,797
Securities held to maturity	73,749	80,463
Other investments, at cost	26,661	14,840
Loans held for sale	3,155	9,562
Derivative financial instruments	3,589	4,016
Portfolio loans, net	4,054,473	3,114,752
State tax credits held for sale	43,468	38,071
Accrued interest receivable	14,069	11,117
Balance sheet liabilities
Deposits	4,156,414	3,233,361
Subordinated debentures and notes	118,105	105,540
Federal Home Loan Bank advances	172,743	0
Other borrowings	253,674	276,980
Derivative financial instruments	3,589	4,016
Accrued interest payable	1,730	1,105
Estimated fair value
Balance sheet assets
Cash and due from banks	91,084	54,288
Federal funds sold	1,223	446
Interest-bearing deposits	63,661	145,048
Securities available for sale	641,382	460,797
Securities held to maturity	73,458	79,639
Other investments, at cost	26,661	14,840
Loans held for sale	3,155	9,562
Derivative financial instruments	3,589	4,016
Portfolio loans, net	4,096,741	3,125,701
State tax credits held for sale	44,271	41,264
Accrued interest receivable	14,069	11,117
Balance sheet liabilities
Deposits	4,153,323	3,232,414
Subordinated debentures and notes	105,031	86,052
Federal Home Loan Bank advances	172,893	0
Other borrowings	253,530	276,905
Derivative financial instruments	3,589	4,016
Accrued interest payable	$ 1,730	$ 1,105

Fair Value Measurements - Sc104

Fair Value Measurements - Schedule of Estimated Fair Values of Financial Instruments Not Recorded at Fair Value on Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Estimated fair value | Securities held to maturity
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial assets not on condensed consolidated balance sheets at fair value	$ 73,458	$ 79,639
Estimated fair value | Portfolio loans, net
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial assets not on condensed consolidated balance sheets at fair value	4,096,741	3,125,701
Estimated fair value | State tax credits, held for sale
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial assets not on condensed consolidated balance sheets at fair value	43,871	37,679
Estimated fair value | Deposits
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	4,153,323	3,232,414
Estimated fair value | Subordinated debentures and notes
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	105,031	86,052
Estimated fair value | Federal Home Loan Bank advances
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	172,893	0
Estimated fair value | Other Borrowings
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	253,530	276,905
Level 1 | Securities held to maturity
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial assets not on condensed consolidated balance sheets at fair value	0	0
Level 1 | Portfolio loans, net
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial assets not on condensed consolidated balance sheets at fair value	0	0
Level 1 | State tax credits, held for sale
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial assets not on condensed consolidated balance sheets at fair value	0	0
Level 1 | Deposits
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	3,577,641	2,760,202
Level 1 | Subordinated debentures and notes
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	0	0
Level 1 | Federal Home Loan Bank advances
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	0	0
Level 1 | Other Borrowings
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	0	0
Level 2 | Securities held to maturity
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial assets not on condensed consolidated balance sheets at fair value	73,458	79,639
Level 2 | Portfolio loans, net
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial assets not on condensed consolidated balance sheets at fair value	0	0
Level 2 | State tax credits, held for sale
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial assets not on condensed consolidated balance sheets at fair value	0	0
Level 2 | Deposits
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	0	0
Level 2 | Subordinated debentures and notes
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	105,031	86,052
Level 2 | Federal Home Loan Bank advances
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	172,893	0
Level 2 | Other Borrowings
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	253,530	276,905
Level 3 | Securities held to maturity
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial assets not on condensed consolidated balance sheets at fair value	0	0
Level 3 | Portfolio loans, net
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial assets not on condensed consolidated balance sheets at fair value	4,096,741	3,125,701
Level 3 | State tax credits, held for sale
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial assets not on condensed consolidated balance sheets at fair value	43,871	37,679
Level 3 | Deposits
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	575,682	472,212
Level 3 | Subordinated debentures and notes
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	0	0
Level 3 | Federal Home Loan Bank advances
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	0	0
Level 3 | Other Borrowings
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	$ 0	$ 0

Parent Company Only Condense105

Parent Company Only Condensed Financial Statements - Condensed Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Cash	$ 153,323	$ 198,802	$ 94,157	$ 100,696
Total assets	5,289,225	4,081,328
Subordinated debentures and notes (net of debt issuance cost of $1,136 and $1,267, respectively)	118,105	105,540
Shareholders' equity	548,573	387,098	350,829	316,241
Total liabilities and shareholders' equity	5,289,225	4,081,328
Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Cash	9,977	52,245	$ 12,032	$ 14,532
Other assets	28,741	22,111
Total assets	668,703	493,985
Subordinated debentures and notes (net of debt issuance cost of $1,136 and $1,267, respectively)	118,105	105,540
Accounts payable and other liabilities	2,025	1,347
Shareholders' equity	548,573	387,098
Total liabilities and shareholders' equity	668,703	493,985
Enterprise Bank and Trust [Member] | Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Investments	623,439	416,831
Nonbank Subsidiaries [Member] | Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Investments	$ 6,546	$ 2,798

Parent Company Only Condense106

Parent Company Only Condensed Financial Statements - Condensed Statements of Operations (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Income [Abstract]
Dividends from subsidiaries									$ 449	$ 226	$ 141
Operating Expenses [Abstract]
Interest expense-subordinated debentures and notes									5,095	1,894	1,248
Interest expense-notes payable	$ 7,385	$ 6,843	$ 5,909	$ 5,098	$ 3,984	$ 3,463	$ 3,250	$ 3,032	25,235	13,729	12,369
Income tax benefit	(19,820)	(7,856)	(5,545)	(5,106)	(7,053)	(6,316)	(6,747)	(5,886)	(38,327)	(26,002)	(19,951)
Net income	$ 7,529	$ 16,315	$ 11,955	$ 12,391	$ 13,628	$ 11,832	$ 12,352	$ 11,025	48,190	48,837	38,450
Total comprehensive income									46,113	46,878	36,987
Parent [Member]
Operating Income [Abstract]
Dividends from subsidiaries									20,000	7,500	10,000
Other									708	491	249
Total income									20,708	7,991	10,249
Operating Expenses [Abstract]
Interest expense-subordinated debentures and notes									5,094	1,893	1,248
Interest expense-notes payable									89	53	144
Other expenses									5,486	5,526	3,823
Total expenses									10,669	7,472	5,215
Income before taxes and equity in undistributed earnings of subsidiaries									10,039	519	5,034
Income tax benefit									3,098	2,583	2,118
Net income									13,137	3,102	7,152
Equity in undistributed earnings of subsidiaries									35,053	45,735	31,298
Total comprehensive income									$ 48,190	$ 48,837	$ 38,450

Parent Company Only Condense107

Parent Company Only Condensed Financial Statements - Consolidated Statements of Cash Flow (Details) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Adjustments to reconcile net income to net cash provided by operating activities:
Share-based compensation	$ 3,427	$ 3,367	$ 3,601
Excess tax benefit of share-based compensation	0	(1,327)	(449)
Net cash provided by operating activities	45,791	82,521	47,187
Cash flows from investing activities:
Net cash paid for acquisitions and dispositions	4,456	0	0
Net cash used in investing activities	(312,444)	(358,057)	(337,250)
Cash flows from financing activities:
Proceeds from the issuance of subordinated notes	0	48,733	0
Proceeds from Notes Payable	10,000	0	0
Repayments of Notes Payable	10,000	0	5,700
Cash dividends paid	(10,249)	(8,211)	(5,259)
Excess tax benefit of share-based compensation	0	1,327	449
Payments for Repurchase of Common Stock	16,636	4,889	0
Net cash provided by financing activities	221,174	380,181	283,524
Net increase (decrease) in cash and cash equivalents	(45,479)	104,645	(6,539)
Cash and cash equivalents, beginning of period	198,802	94,157	100,696
Cash and cash equivalents, end of period	$ 153,323	$ 198,802	$ 94,157
Noncash transactions:
Stock Issued During Period, Shares, Acquisitions	141,729	0	0
Parent [Member]
Cash flows from operating activities:
Net income available to common shareholders	$ 48,190	$ 48,837	$ 38,450
Adjustments to reconcile net income to net cash provided by operating activities:
Share-based compensation	3,427	3,367	3,601
Net income of subsidiaries	(55,053)	(53,235)	(41,298)
Dividends from subsidiaries	20,000	7,500	10,000
Excess tax benefit of share-based compensation	0	(1,327)	(449)
Other, net	(1,806)	1,848	848
Net cash provided by operating activities	14,758	6,990	11,152
Cash flows from investing activities:
Cash contributions to subsidiaries	0	(250)	0
Net cash paid for acquisitions and dispositions	(25,187)	0	0
Purchases of other investments	(3,679)	(2,435)	(2,832)
Proceeds from distributions on other investments	1,634	1,151	880
Net cash used in investing activities	(27,232)	(1,534)	(1,952)
Cash flows from financing activities:
Proceeds from the issuance of subordinated notes	0	48,733	0
Proceeds from Notes Payable	10,000	0	0
Repayments of Notes Payable	10,000	0	5,700
Cash dividends paid	(10,249)	(8,211)	(5,259)
Excess tax benefit of share-based compensation	0	1,327	449
Payments for Repurchase of Common Stock	16,636	4,889	0
Payments for the repurchase of equity instruments, net	(2,909)	(2,203)	(1,190)
Net cash provided by financing activities	(29,794)	34,757	(11,700)
Net increase (decrease) in cash and cash equivalents	(42,268)	40,213	(2,500)
Cash and cash equivalents, beginning of period	52,245	12,032	14,532
Cash and cash equivalents, end of period	$ 9,977	$ 52,245	$ 12,032
Noncash transactions:
Stock Issued During Period, Shares, Acquisitions	141,729	0	0

Quarterly Condensed Financia108

Quarterly Condensed Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Interest income	$ 54,789	$ 52,468	$ 51,542	$ 43,740	$ 39,438	$ 37,293	$ 37,033	$ 35,460	$ 202,539	$ 149,224	$ 132,779
Interest expense	7,385	6,843	5,909	5,098	3,984	3,463	3,250	3,032	25,235	13,729	12,369
Net interest income	47,404	45,625	45,633	38,642	35,454	33,830	33,783	32,428	177,304	135,495	120,410
Provision for portfolio loan losses	3,186	2,422	3,623	1,533	964	3,038	716	833	10,764	5,551	4,872
Provision reversal for purchased credit impaired loan losses	(279)	0	(207)	(148)	(343)	(1,194)	(336)	(73)	(634)	(1,946)	(4,414)
Net interest income after provision for loan losses	44,497	43,203	42,217	37,257	34,833	31,986	33,403	31,668	167,174	131,890	119,952
Noninterest income	11,112	8,372	7,934	6,976	9,029	6,976	7,049	6,005	34,394	29,059	20,675
Noninterest expense	28,260	27,404	32,651	26,736	23,181	20,814	21,353	20,762	115,051	86,110	82,226
Income before income tax expense	27,349	24,171	17,500	17,497	20,681	18,148	19,099	16,911	86,517	74,839	58,401
Income tax expense	19,820	7,856	5,545	5,106	7,053	6,316	6,747	5,886	38,327	26,002	19,951
Net income	$ 7,529	$ 16,315	$ 11,955	$ 12,391	$ 13,628	$ 11,832	$ 12,352	$ 11,025	$ 48,190	$ 48,837	$ 38,450
Earnings per common share:
Basic (usd per share)	$ 0.33	$ 0.70	$ 0.51	$ 0.57	$ 0.68	$ 0.59	$ 0.62	$ 0.55	$ 2.10	$ 2.44	$ 1.92
Diluted (usd per share)	$ 0.32	$ 0.69	$ 0.50	$ 0.56	$ 0.67	$ 0.59	$ 0.61	$ 0.54	$ 2.07	$ 2.41	$ 1.89