STOCKHOLDERS’ EQUITY - Schedule of Company's Significant Subsidiaries (Details) $ in Thousands	Dec. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)
Class of Stock [Line Items]
Capital Required to be Well Capitalized to Risk Weighted Assets	0.10
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	0.08
Tier One Leverage Capital Required to be Well Capitalized to Average Assets	0.05
Simmons First National Corporation
Class of Stock [Line Items]
Capital	$ 2,906,684	$ 2,992,132
Capital to Risk Weighted Assets	0.145	0.146
Capital Required for Capital Adequacy	$ 1,603,688	$ 1,639,524
Capital Required for Capital Adequacy to Risk Weighted Assets	0.080	0.080
Tier One Risk Based Capital	$ 2,338,965	$ 2,535,527
Tier One Risk Based Capital to Risk Weighted Assets	0.116	0.124
Tier One Risk Based Capital Required for Capital Adequacy	$ 1,209,809	$ 1,226,868
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	0.060	0.060
Common Equity Tier One Capital	$ 2,338,965	$ 2,535,527
Common Equity Tier One Capital Ratio	0.116	0.124
Common Equity Tier One Capital Required for Capital Adequacy	$ 907,357	$ 920,151
Common Equity Tier One Capital Required for Capital Adequacy to Risk Weighted Assets	4.50%	4.50%
Tier One Leverage Capital	$ 2,338,965	$ 2,535,527
Tier One Leverage Capital to Average Assets	0.101	0.097
Tier One Leverage Capital Required for Capital Adequacy	$ 926,323	$ 1,045,578
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	0.040	0.040
Simmons Bank
Class of Stock [Line Items]
Capital	$ 2,367,449	$ 2,795,430
Capital to Risk Weighted Assets	0.118	0.137
Capital Required for Capital Adequacy	$ 1,605,050	$ 1,632,368
Capital Required for Capital Adequacy to Risk Weighted Assets	0.080	0.080
Capital Required to be Well Capitalized	$ 2,006,313	$ 2,040,460
Capital Required to be Well Capitalized to Risk Weighted Assets	0.100	0.100
Tier One Risk Based Capital	$ 2,117,443	$ 2,573,121
Tier One Risk Based Capital to Risk Weighted Assets	0.106	0.126
Tier One Risk Based Capital Required for Capital Adequacy	$ 1,198,553	$ 1,225,296
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	0.060	0.060
Tier One Risk Based Capital Required to be Well Capitalized	$ 1,598,070	$ 1,633,728
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	0.080	0.080
Common Equity Tier One Capital	$ 2,117,443	$ 2,573,121
Common Equity Tier One Capital Ratio	0.106	0.126
Common Equity Tier One Capital Required for Capital Adequacy	$ 898,914	$ 918,972
Common Equity Tier One Capital Required for Capital Adequacy to Risk Weighted Assets	4.50%	4.50%
Common Equity Tier One Capital Required to be Well-Capitalized	$ 1,298,432	$ 1,327,404
Common Equity Tier One Capital Required to Be Well Capitalized to Risk Weighted Assets	6.50%	6.50%
Tier One Leverage Capital	$ 2,117,443	$ 2,573,121
Tier One Leverage Capital to Average Assets	0.091	0.099
Tier One Leverage Capital Required for Capital Adequacy	$ 930,744	$ 1,039,645
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	0.040	0.040
Tier One Leverage Capital Required to be Well Capitalized	$ 1,163,430	$ 1,299,556
Tier One Leverage Capital Required to be Well Capitalized to Average Assets	0.050	0.050