Subordinated Debentures (Details) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Subordinated Borrowing [Line Items]
Subordinated debentures and notes	$ 203,510	$ 141,258
Trust Preferred Securities Subject to Mandatory Redemption [Member]
Subordinated Borrowing [Line Items]
Subordinated debentures and notes	92,253	92,132
Trust Preferred Securities Subject to Mandatory Redemption [Member] | EFSC Clayco Statutory Trust I [Member]
Subordinated Borrowing [Line Items]
Subordinated debentures and notes	$ 3,196	3,196
Subordinated Borrowing, Due Date	Dec. 17, 2033
Subordinated Borrowing, Call Date	Dec. 17, 2008
Trust Preferred Securities Subject to Mandatory Redemption [Member] | EFSC Clayco Statutory Trust I [Member] | London Interbank Offered Rate (LIBOR) [Member]
Subordinated Borrowing [Line Items]
Subordinated Borrowing, Basis Spread on Variable Rate	0.0285
Trust Preferred Securities Subject to Mandatory Redemption [Member] | EFSC Capital Trust II [Member]
Subordinated Borrowing [Line Items]
Subordinated debentures and notes	$ 5,155	5,155
Subordinated Borrowing, Due Date	Jun. 17, 2034
Subordinated Borrowing, Call Date	Jun. 17, 2009
Trust Preferred Securities Subject to Mandatory Redemption [Member] | EFSC Capital Trust II [Member] | London Interbank Offered Rate (LIBOR) [Member]
Subordinated Borrowing [Line Items]
Subordinated Borrowing, Basis Spread on Variable Rate	0.0265
Trust Preferred Securities Subject to Mandatory Redemption [Member] | EFSC Statutory Trust III [Member]
Subordinated Borrowing [Line Items]
Subordinated debentures and notes	$ 11,341	11,341
Subordinated Borrowing, Due Date	Dec. 15, 2034
Subordinated Borrowing, Call Date	Dec. 15, 2009
Trust Preferred Securities Subject to Mandatory Redemption [Member] | EFSC Statutory Trust III [Member] | London Interbank Offered Rate (LIBOR) [Member]
Subordinated Borrowing [Line Items]
Subordinated Borrowing, Basis Spread on Variable Rate	0.0197
Trust Preferred Securities Subject to Mandatory Redemption [Member] | EFSC Clayco Statutory Trust II [Member]
Subordinated Borrowing [Line Items]
Subordinated debentures and notes	$ 4,124	4,124
Subordinated Borrowing, Due Date	Sep. 15, 2035
Subordinated Borrowing, Call Date	Sep. 15, 2010
Trust Preferred Securities Subject to Mandatory Redemption [Member] | EFSC Clayco Statutory Trust II [Member] | London Interbank Offered Rate (LIBOR) [Member]
Subordinated Borrowing [Line Items]
Subordinated Borrowing, Basis Spread on Variable Rate	0.0183
Trust Preferred Securities Subject to Mandatory Redemption [Member] | EFSC Statutory Trust IV [Member]
Subordinated Borrowing [Line Items]
Subordinated debentures and notes	$ 10,310	10,310
Subordinated Borrowing, Due Date	Dec. 15, 2035
Subordinated Borrowing, Call Date	Dec. 15, 2010
Trust Preferred Securities Subject to Mandatory Redemption [Member] | EFSC Statutory Trust IV [Member] | London Interbank Offered Rate (LIBOR) [Member]
Subordinated Borrowing [Line Items]
Subordinated Borrowing, Basis Spread on Variable Rate	0.0144
Trust Preferred Securities Subject to Mandatory Redemption [Member] | EFSC Statutory Trust V [Member]
Subordinated Borrowing [Line Items]
Subordinated debentures and notes	$ 4,124	4,124
Subordinated Borrowing, Due Date	Sep. 15, 2036
Subordinated Borrowing, Call Date	Sep. 15, 2011
Trust Preferred Securities Subject to Mandatory Redemption [Member] | EFSC Statutory Trust V [Member] | London Interbank Offered Rate (LIBOR) [Member]
Subordinated Borrowing [Line Items]
Subordinated Borrowing, Basis Spread on Variable Rate	0.0160
Trust Preferred Securities Subject to Mandatory Redemption [Member] | EFSC Capital Trust VI [Member]
Subordinated Borrowing [Line Items]
Subordinated debentures and notes	$ 14,433	14,433
Subordinated Borrowing, Due Date	Mar. 30, 2037
Subordinated Borrowing, Call Date	Mar. 30, 2012
Trust Preferred Securities Subject to Mandatory Redemption [Member] | EFSC Capital Trust VI [Member] | London Interbank Offered Rate (LIBOR) [Member]
Subordinated Borrowing [Line Items]
Subordinated Borrowing, Basis Spread on Variable Rate	0.0160
Trust Preferred Securities Subject to Mandatory Redemption [Member] | EFSC Capital Trust VII [Member]
Subordinated Borrowing [Line Items]
Subordinated debentures and notes	$ 4,124	4,124
Subordinated Borrowing, Due Date	Dec. 15, 2037
Subordinated Borrowing, Call Date	Dec. 15, 2012
Trust Preferred Securities Subject to Mandatory Redemption [Member] | EFSC Capital Trust VII [Member] | London Interbank Offered Rate (LIBOR) [Member]
Subordinated Borrowing [Line Items]
Subordinated Borrowing, Basis Spread on Variable Rate	0.0225
Trust Preferred Securities Subject to Mandatory Redemption [Member] | JEFFCO Stat Trust I [Member]
Subordinated Borrowing [Line Items]
Subordinated debentures and notes	$ 7,786	7,886
Subordinated Borrowing, Due Date	Feb. 22, 2031
Subordinated Borrowing, Call Date	Feb. 22, 2011
Subordinated Borrowing, Interest Rate	10.20%
Trust Preferred Securities Subject to Mandatory Redemption [Member] | JEFFCO Stat Trust II [Member]
Subordinated Borrowing [Line Items]
Subordinated debentures and notes	$ 4,429	4,388
Subordinated Borrowing, Due Date	Mar. 17, 2034
Subordinated Borrowing, Call Date	Mar. 17, 2009
Trust Preferred Securities Subject to Mandatory Redemption [Member] | JEFFCO Stat Trust II [Member] | London Interbank Offered Rate (LIBOR) [Member]
Subordinated Borrowing [Line Items]
Subordinated Borrowing, Interest Rate	2.75%
Trust Preferred Securities Subject to Mandatory Redemption [Member] | Trinity Capital Trust III [Member]
Subordinated Borrowing [Line Items]
Subordinated debentures and notes	$ 5,256	5,206
Subordinated Borrowing, Due Date	Sep. 08, 2034
Subordinated Borrowing, Call Date	Sep. 08, 2009
Trust Preferred Securities Subject to Mandatory Redemption [Member] | Trinity Capital Trust III [Member] | London Interbank Offered Rate (LIBOR) [Member]
Subordinated Borrowing [Line Items]
Subordinated Borrowing, Basis Spread on Variable Rate	0.0270
Trust Preferred Securities Subject to Mandatory Redemption [Member] | Trinity Capital Trust IV [Member]
Subordinated Borrowing [Line Items]
Subordinated debentures and notes	$ 10,310	10,302
Subordinated Borrowing, Due Date	Nov. 23, 2035
Subordinated Borrowing, Call Date	Aug. 23, 2010
Subordinated Borrowing, Interest Rate	6.88%
Trust Preferred Securities Subject to Mandatory Redemption [Member] | Trinity Capital Trust V [Member]
Subordinated Borrowing [Line Items]
Subordinated debentures and notes	$ 7,665	7,543
Subordinated Borrowing, Due Date	Dec. 15, 2036
Subordinated Borrowing, Call Date	Sep. 15, 2011
Trust Preferred Securities Subject to Mandatory Redemption [Member] | Trinity Capital Trust V [Member] | London Interbank Offered Rate (LIBOR) [Member]
Subordinated Borrowing [Line Items]
Subordinated Borrowing, Basis Spread on Variable Rate	0.0165
Senior Subordinated Notes [Member]
Subordinated Borrowing [Line Items]
Subordinated Borrowing, Interest Rate	4.75%
Payments of Debt Issuance Costs	$ 1,993	874
Subordinated notes, net of issuance costs	$ 111,257	49,126
Senior Subordinated Notes [Member] | London Interbank Offered Rate (LIBOR) [Member]
Subordinated Borrowing [Line Items]
Subordinated Borrowing, Basis Spread on Variable Rate	0.03387
Senior Subordinated Notes [Member] | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Subordinated Borrowing [Line Items]
Subordinated Borrowing, Basis Spread on Variable Rate	0.0566
5.75% [Member] | Senior Subordinated Notes [Member]
Subordinated Borrowing [Line Items]
Subordinated debentures and notes	$ 63,250	0
Subordinated Borrowing, Due Date	Jun. 01, 2030
Subordinated Borrowing, Call Date	Jun. 01, 2025
Subordinated Borrowing, Interest Rate	5.75%
4.75% [Member] | Senior Subordinated Notes [Member]
Subordinated Borrowing [Line Items]
Subordinated debentures and notes	$ 50,000	$ 50,000
Subordinated Borrowing, Due Date	Nov. 01, 2026
Subordinated Borrowing, Call Date	Nov. 01, 2021