Right-Of-Use Lease Assets and Lease Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Leases [Abstract]
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
Lease liability included in other liabilities	$ 34,800	$ 40,900
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrent	us-gaap:AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrent