Premises and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Right-of-use lease assets	$ 31,348	$ 40,675
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	sfnc:PropertyPlantandEquipmentandRightofUseAssetafterAccumulatedDepreciationandAmortization	sfnc:PropertyPlantandEquipmentandRightofUseAssetafterAccumulatedDepreciationandAmortization
Accumulated depreciation and amortization	$ (140,450)	$ (119,865)
Total premises and equipment, net	441,692	492,384
Land
Property, Plant and Equipment [Line Items]
Premises and equipment	90,953	99,931
Buildings and improvements
Property, Plant and Equipment [Line Items]
Premises and equipment	293,338	309,290
Furniture, fixtures and equipment
Property, Plant and Equipment [Line Items]
Premises and equipment	100,863	99,343
Software
Property, Plant and Equipment [Line Items]
Premises and equipment	64,877	56,012
Construction in progress
Property, Plant and Equipment [Line Items]
Premises and equipment	$ 763	$ 6,998