Loans and Allowance for Loan Losses - Loan Portfolio by Categories (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	$ 14,430,000	$ 11,720,000
Loans acquired, net of discount and allowance	4,795,184	3,292,783
Total loans	14,425,260	11,723,171
Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	9,630,076	8,430,388
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	396,748	405,470
Consumer \| Credit cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	204,802	204,173
Consumer \| Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	191,946	201,297
Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	6,884,422	5,966,453
Real Estate \| Construction and development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	1,760,894	1,300,723
Real Estate \| Single family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	1,444,620	1,440,443
Real Estate \| Other commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	3,678,908	3,225,287
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	2,073,192	1,939,423
Commercial \| Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	1,909,796	1,774,909
Commercial \| Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	163,396	164,514
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	$ 275,714	$ 119,042

Loans acquired which are not covered by FDIC loss share agreements, net of discount.

No definition available.

Name:	sfnc_LoansAcquiredNotCoveredByFDICLossShareNetOfDiscount
Namespace Prefix:	sfnc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Loans and leases receivable, net of deferred income covered and not covered

+ References

No definition available.

+ Details

Name:	sfnc_LoansAndLeasesReceivableNetOfDeferredIncomeCoveredAndNotCovered
Namespace Prefix:	sfnc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_AccountsNotesAndLoansReceivableLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=118952595&loc=d3e4428-111522

+ Details

Name:	us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=sfnc_LoansExcludingAcquiredLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CreditCardReceivablesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sfnc_OtherConsumerLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=sfnc_RealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConstructionLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=srt_SingleFamilyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sfnc_OtherCommercialLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sfnc_CommercialLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sfnc_AgriculturalLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_UnallocatedFinancingReceivablesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: