Acquisitions & Divestitures - Summary of Balance Sheet Amounts Relative to Branches Sold (Details)	3 Months Ended
	Mar. 31, 2017 USD ($) $ / shares	Mar. 31, 2016 USD ($) $ / shares	Feb. 10, 2017 USD ($)	Dec. 31, 2016 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net income as reported	$ 12,391,000	$ 11,025,000
Cash and cash equivalents	209,001,000			$ 198,802,000
Property, Plant and Equipment, Net	34,291,000			14,910,000
Interest Receivable	12,229,000			11,117,000
Goodwill	113,886,000			30,334,000
Other Intangible Assets	11,758,000			2,151,000
Deposits	4,031,620,000			3,233,361,000
Other Borrowings	235,052,000			276,980,000
Interest Payable	1,914,000			1,105,000
Other Liabilities	$ 30,537,000			$ 77,244,000
Total cash paid to JCB shareholders and holders of JCB stock options			$ 29,300,000
Common shares issued related to acquisition	141,729,000			0
Transaction value including JCB's common stock and stock options			171,000,000
Business Acquisition, Goodwill, Expected Tax Deductible Amount			83,600,000
Pro Forma [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenues	$ 49,598,000	47,275,000
Net income as reported	$ 13,054,000	$ 12,961,000
Diluted Earnings Per Share Pro Forma | $ / shares	$ 0.55	$ 0.55
As Recorded by JCB [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and cash equivalents			35,454,000
Securities			148,670,000
Portfolio loans, net			685,905,000
Other real estate owned			6,762,000
Other Investments			2,695,000
Property, Plant and Equipment, Net			21,780,000
Interest Receivable			2,794,000
Goodwill			7,806,000
Other Intangible Assets			25,000
Deferred Tax Assets			4,634,000
Other Assets			19,159,000
Total assets acquired			935,684,000
Deposits			764,668,000
Other Borrowings			55,430,000
Trust preferred securities			12,887,000
Interest Payable			653,000
Other Liabilities			5,006,000
Total Liabilities Assumed			838,644,000
Net assets acquired			97,040,000
Adjustments associated with acquisition [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and cash equivalents			0
Securities			0
Portfolio loans, net			(10,619,000)
Other real estate owned			(5,082,000)
Other Investments			0
Property, Plant and Equipment, Net			(2,259,000)
Interest Receivable			0
Goodwill			(7,806,000)
Other Intangible Assets			10,028,000
Deferred Tax Assets			7,086,000
Other Assets			0
Total assets acquired			(8,652,000)
Deposits			629,000
Other Borrowings			681,000
Trust preferred securities			(382,000)
Interest Payable			0
Other Liabilities			0
Total Liabilities Assumed			928,000
Net assets acquired			(9,580,000)
As Recorded by EFSC [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and cash equivalents			35,454,000
Securities			148,670,000
Portfolio loans, net			675,286,000
Other real estate owned			1,680,000
Other Investments			2,695,000
Property, Plant and Equipment, Net			19,521,000
Interest Receivable			2,794,000
Goodwill			0
Other Intangible Assets			10,053,000
Deferred Tax Assets			11,720,000
Other Assets			19,159,000
Total assets acquired			927,032,000
Deposits			765,297,000
Other Borrowings			56,111,000
Trust preferred securities			12,505,000
Interest Payable			653,000
Other Liabilities			5,006,000
Total Liabilities Assumed			839,572,000
Net assets acquired			87,460,000
Total cash paid to JCB shareholders and holders of JCB stock options			29,283,000
Common shares issued related 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			$ 83,552,000.00