Premises and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Right-of-use lease assets	$ 34,680	$ 40,675
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	sfnc:PropertyPlantandEquipmentandRightofUseAssetafterAccumulatedDepreciationandAmortization	sfnc:PropertyPlantandEquipmentandRightofUseAssetafterAccumulatedDepreciationandAmortization
Accumulated depreciation and amortization	$ (128,355)	$ (119,865)
Total premises and equipment, net	478,896	492,384
Land
Property, Plant and Equipment [Line Items]
Premises and equipment	96,607	99,931
Buildings and improvements
Property, Plant and Equipment [Line Items]
Premises and equipment	306,951	309,290
Furniture, fixtures and equipment
Property, Plant and Equipment [Line Items]
Premises and equipment	98,383	99,343
Software
Property, Plant and Equipment [Line Items]
Premises and equipment	63,995	56,012
Construction in progress
Property, Plant and Equipment [Line Items]
Premises and equipment	$ 6,635	$ 6,998