Mortgage Banking Activities - Key Economic Assumptions in Measuring Value of Mortgage Servicing Rights (Detail)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Mortgage Banking [Abstract]
Weighted average prepayment rate	181.00%	165.00%
Weighted average life (in years)	6 years 4 months 6 days	6 years 7 months 20 days
Weighted average discount rate	9.00%	9.00%

No definition available.

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- Definition

Discount rate used to estimate the fair value of servicing assets and servicing liabilities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 2
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122596-111746

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- Definition

Estimated rate of prepayments of principal on servicing assets and servicing liabilities.

+ References

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- Definition

Weighted average life of financial assets and financial liabilities, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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