Represents the total number of common stock shares which can be issued under the plan.

No definition available.

Name:	inbk_CommonStockSharesReservedForFutureIssuance
Namespace Prefix:	inbk_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The description of employer matching contribution under defined contribution plan.

+ References

No definition available.

+ Details

Name:	inbk_DefinedContributionPlanEmployerMatchingContributionDescription
Namespace Prefix:	inbk_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Defined Contribution Plan, Employer Matching Contribution, Period of Match

+ References

No definition available.

+ Details

Name:	inbk_DefinedContributionPlanEmployerMatchingContributionPeriodofMatch
Namespace Prefix:	inbk_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents the percentage of directors annual retention in either common stock or deferred stock rights under directors deferred stock plan.

+ References

No definition available.

+ Details

Name:	inbk_DirectorsDeferredStockPlanPercentage
Namespace Prefix:	inbk_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
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-Name Accounting Standards Codification
-Topic 718
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-Section S99
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-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

+ Details

Name:	us-gaap_AllocatedShareBasedCompensationExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of discretionary contributions made by an employer to a defined contribution plan.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Percentage employer matches of the employee's percentage contribution matched.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of employer's matching contributions to a defined contribution plan that vests in a given year.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedContributionPlanEmployersMatchingContributionAnnualVestingPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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

- Definition

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

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

- Definition

Number of shares authorized for issuance under share-based payment arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=inbk_EquityIncentivePlan2013Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=inbk_DirectorsDeferredStockPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Benefit Plans (Details Textual) - USD ($) $ in Millions	12 Months Ended
Benefit Plans (Details Textual) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contributions	$ 0.6	$ 0.5	$ 0.5
Vesting (as a percent)	50.00%
Unrecognized compensation cost	$ 2.0
Weighted average expense recognition period (in years)	1 year 9 months 18 days
Employer matching contribution description	The Company has a 401(k) plan established for substantially all full-time employees, as defined. Employee contributions are limited to the maximum established by the Internal Revenue Service on an annual basis. The Company has elected to match contributions equal to 100% of the first 1% of employee deferrals and then 50% on deferrals over 1% up to a maximum of 6% of an individuals total eligible salary, as defined by the plan.
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee deferral (as a percent)	1.00%
Vesting period (in years)	1 year
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee deferral (as a percent)	6.00%
Vesting period (in years)	2 years
Equity Incentive Plan 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized	750,000
Share-based compensation expense	$ 1.7	$ 1.6	$ 1.0
Directors Deferred Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contributions (as a percent)	100.00%
Employee deferral (as a percent)	1.00%
Number of shares available for future issuance	180,000