Summary Of Significant Accounting And Reporting Policies (Details) $ in Thousands		12 Months Ended
	Oct. 09, 2015 USD ($)	Dec. 31, 2016 USD ($) entity item shares	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 USD ($) shares
Number Of Total Branches | item		1
Interest-bearing balances held at depository institutions		$ 38,800	$ 53,200
Interest paid		9,700	7,000	$ 6,900
Income taxes paid		9,400	7,100	4,000
Stock issued for Bancshares acquisition	$ 21,400		21,366
Other real estate		350	2,274
Transfer to Other Real Estate		500	300	2,200
Restricted cash and cash equivalents		$ 1,000	7,000
Threshold Period Past Due for Write-off of Financing Receivable		90 days
Net unamortized deferred loan fees		$ 2,500	1,500
Assets, Total		2,475,392	2,357,022	1,214
Deposits, Total		$ 1,946,018	1,884,105	$ 1,533,999
Number Of Days For Independent Appraisals On Real Estate Collateral		30 days
Reserve For Unfunded Loan Commitments		$ 2,500	$ 2,400
Antidilutive options to purchase common shares | shares		6,573	38,145	0
Fair value of loan servicing rights		$ 4,200	$ 3,700
Simmons First National Corporation [Member]
Number Of Total Branches | entity		150
Assets, Total		$ 8,400
Deposits, Total		6,700
Loans and Leases Receivable, Net Reported Amount		$ 5,600
Minimum [Member]
Percentage change in fair value to be considered highly effective		80.00%
Stock option expiration period after grant		5 years
Minimum [Member] | Building and Building Improvements [Member]
Premises and equipmet, useful life		10 years
Minimum [Member] | Furniture, Fixtures and Equipment [Member]
Premises and equipmet, useful life		3 years
Maximum [Member]
Percentage change in fair value to be considered highly effective		125.00%
Stock option expiration period after grant		10 years
Maximum [Member] | Building and Building Improvements [Member]
Premises and equipmet, useful life		40 years
Maximum [Member] | Furniture, Fixtures and Equipment [Member]
Premises and equipmet, useful life		10 years
2008 Stock Based Award Plan [Member]
Stock Plan Term		10 years
Common stock reserved for issuance | shares		800,000