Amortized cost of financing receivable on nonaccrual status. Excludes net investment in lease.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=123577603&loc=d3e5111-111524

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 16
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919258-210447

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph (a)
-Subparagraph (3)

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph (a)
-Subparagraph (2)

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus
Namespace Prefix:	us-gaap_
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_FinancingReceivableRecordedInvestmentPastDueLineItems
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 https://asc.fasb.org/extlink&oid=124259787&loc=d3e4428-111522

+ Details

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

- Definition

Amortized cost, before allowance for credit loss, of financing receivable. Excludes financing receivable covered under loss sharing agreement and net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7A
-URI https://asc.fasb.org/extlink&oid=123577603&loc=SL6953401-111524

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 79
-URI https://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(3)(b))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 14
-URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919253-210447

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919230-210447

Reference 7: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 80
-URI https://asc.fasb.org/extlink&oid=124267575&loc=SL82922355-210448

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph (a)
-Subparagraph (1)

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph (a)
-Subparagraph (2)

Reference 10: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1404
-Paragraph (a)

+ Details

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

- Details

Name:	us-gaap_FinancingReceivablesPeriodPastDueAxis=ck0001641601_FinancingReceivables30To89DaysPastDueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablesPeriodPastDueAxis=us-gaap_FinancialAssetNotPastDueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_HomeEquityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=ck0001641601_ConstructionAndLandDevelopmentMember
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_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

Loans, Allowance for Loan Losses and Credit Quality - Summary of Aging of Loans and Non-accrual Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021
Financing Receivable Recorded Investment Past Due [Line Items]
Nonaccrual Loans	$ 1,487	$ 2,272
Total Loans	1,459,830	1,273,039	$ 1,236,200
Past Due 30-89 Days
Financing Receivable Recorded Investment Past Due [Line Items]
Accruing Loans, Current	2,023	3,552
Current
Financing Receivable Recorded Investment Past Due [Line Items]
Accruing Loans, Current	1,456,320	1,267,215
Home Equity Lines of Credit
Financing Receivable Recorded Investment Past Due [Line Items]
Nonaccrual Loans	168	252
Total Loans	53,167	49,569
Home Equity Lines of Credit \| Past Due 30-89 Days
Financing Receivable Recorded Investment Past Due [Line Items]
Accruing Loans, Current	94	88
Home Equity Lines of Credit \| Current
Financing Receivable Recorded Investment Past Due [Line Items]
Accruing Loans, Current	52,905	49,229
Commercial Real Estate
Financing Receivable Recorded Investment Past Due [Line Items]
Total Loans	442,698	389,181
Construction and Land Development
Financing Receivable Recorded Investment Past Due [Line Items]
Total Loans	241,084	196,116
Commercial Loans
Financing Receivable Recorded Investment Past Due [Line Items]
Total Loans	254,345	261,924	313,115
Commercial Loans \| Past Due 30-89 Days
Financing Receivable Recorded Investment Past Due [Line Items]
Accruing Loans, Current	470	304
Commercial Loans \| Current
Financing Receivable Recorded Investment Past Due [Line Items]
Accruing Loans, Current	253,875	261,620
Consumer Loans
Financing Receivable Recorded Investment Past Due [Line Items]
Nonaccrual Loans	19	112
Total Loans	45,161	43,080	42,069
Consumer Loans \| Past Due 30-89 Days
Financing Receivable Recorded Investment Past Due [Line Items]
Accruing Loans, Current	557	201
Consumer Loans \| Current
Financing Receivable Recorded Investment Past Due [Line Items]
Accruing Loans, Current	44,585	42,767
Residential Real Estate
Financing Receivable Recorded Investment Past Due [Line Items]
Total Loans	423,375	333,169
Mortgage Loans on Real Estate
Financing Receivable Recorded Investment Past Due [Line Items]
Nonaccrual Loans	1,300	1,908
Total Loans	1,107,157	918,466
Mortgage Loans on Real Estate \| Past Due 30-89 Days
Financing Receivable Recorded Investment Past Due [Line Items]
Accruing Loans, Current	902	2,959
Mortgage Loans on Real Estate \| Current
Financing Receivable Recorded Investment Past Due [Line Items]
Accruing Loans, Current	1,104,955	913,599
Mortgage Loans on Real Estate \| Home Equity Lines of Credit
Financing Receivable Recorded Investment Past Due [Line Items]
Total Loans	53,167		44,179
Mortgage Loans on Real Estate \| Commercial Real Estate
Financing Receivable Recorded Investment Past Due [Line Items]
Nonaccrual Loans	635	885
Total Loans	442,698	389,181	386,478
Mortgage Loans on Real Estate \| Commercial Real Estate \| Past Due 30-89 Days
Financing Receivable Recorded Investment Past Due [Line Items]
Accruing Loans, Current		1,193
Mortgage Loans on Real Estate \| Commercial Real Estate \| Current
Financing Receivable Recorded Investment Past Due [Line Items]
Accruing Loans, Current	442,063	387,103
Mortgage Loans on Real Estate \| Construction and Land Development
Financing Receivable Recorded Investment Past Due [Line Items]
Nonaccrual Loans	10	11
Total Loans	241,084	196,116	164,199
Mortgage Loans on Real Estate \| Construction and Land Development \| Past Due 30-89 Days
Financing Receivable Recorded Investment Past Due [Line Items]
Accruing Loans, Current	369	327
Mortgage Loans on Real Estate \| Construction and Land Development \| Current
Financing Receivable Recorded Investment Past Due [Line Items]
Accruing Loans, Current	240,705	195,778
Mortgage Loans on Real Estate \| Residential Real Estate
Financing Receivable Recorded Investment Past Due [Line Items]
Nonaccrual Loans	655	1,012
Total Loans	423,375	333,169	$ 286,160
Mortgage Loans on Real Estate \| Residential Real Estate \| Past Due 30-89 Days
Financing Receivable Recorded Investment Past Due [Line Items]
Accruing Loans, Current	533	1,439
Mortgage Loans on Real Estate \| Residential Real Estate \| Current
Financing Receivable Recorded Investment Past Due [Line Items]
Accruing Loans, Current	$ 422,187	$ 330,718