Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Additional Information (Details 3) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2017 USD ($) Loan Factor	Sep. 30, 2017 Loan Factor Scale
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Number of loan types for commercial portfolio \| Loan	9	9
Number of risk rate factors for commercial loans \| Factor	450	450
Minimum score for qualitative risk factor \| Scale		0
Maximum score for qualitative risk factor \| Scale		100
Number of loan types for consumer portfolio \| Loan	5	5
Number of unique qualitative factors used to analyze consumer loans \| Factor	5	5
Texas [Member] \| Hurricane Harvey [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Increase in allowance for loan losses \| $	$ 1.1

The number of unique loan types the commercial portfolio was delineated into for analysis of loan loss allowance.

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- Definition

The number of unique loan types the consumer portfolio was delineated into for analysis of loan loss allowance.

+ References

No definition available.

+ Details

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- Definition

The number of risk rate factors utilized for the commercial portfolio.

+ References

No definition available.

+ Details

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- Definition

The number of unique qualitative factors used to evaluate the consumer loan portfolio for loan loss allowance.

+ References

No definition available.

+ Details

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- Definition

When presenting a range of scores, the highest potential score under the assessment procedure.

+ References

No definition available.

+ Details

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When presenting a range of scores, the lowest potential score under the assessment procedure.

+ References

No definition available.

+ Details

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- Definition

Amount of increase (decrease) of allowance reserve for credit loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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- References

No definition available.

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