Percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
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_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=fsb_March2016SubordinatedNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SubordinatedDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=fsb_June2016SubordinatedNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

SUBORDINATED DEBT ISSUANCE - Summary of Terms of Each Subordinated Note offering (Detail) - USD ($)	1 Months Ended		3 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Mar. 31, 2020	Dec. 31, 2016	Sep. 30, 2016
Debt Instrument [Line Items]
Principal amount issued	$ 20,000,000	$ 40,000,000
Initial fixed interest rate	7.00%	6.875%
March 2016 Subordinated Notes \| LIBOR
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate		5.636%
Subordinated Debt
Debt Instrument [Line Items]
Principal amount issued			$ 60,000,000
Subordinated Debt \| March 2016 Subordinated Notes
Debt Instrument [Line Items]
Principal amount issued					$ 40,000,000
Initial fixed interest rate					6.875%
Initial interest rate period		5 years	10 years
Subordinated Debt \| June 2016 Subordinated Notes
Debt Instrument [Line Items]
Principal amount issued				$ 20,000,000
Initial fixed interest rate				7.00%
Initial interest rate period	5 years		10 years
Subordinated Debt \| June 2016 Subordinated Notes \| LIBOR
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	6.04%