Derivative Financial Instruments - Schedule of Derivative Financial Instruments on Statements of Income (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Derivatives in hedging relationships	$ (7,390)	$ (30)	$ (813)
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivatives in hedging relationships	(781)	(30)	(813)
Designated as Hedging Instrument [Member] \| Interest Income/ (Expense) [Member] \| Interest Rate Swap Contracts [Member] \| Fair Value Hedging [Member]
Derivative [Line Items]
Derivatives in hedging relationships	(781)	(30)	(813)
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivatives not designated as hedging instruments	(6,609)	0	0
Not Designated as Hedging Instrument [Member] \| Income from Mortgage Banking Activities [Member] \| TBA Mortgage Backed Securities [Member]
Derivative [Line Items]
Derivatives not designated as hedging instruments	1,547	0	0
Not Designated as Hedging Instrument [Member] \| Income from Mortgage Banking Activities [Member] \| Interest Rate Lock Commitments [Member]
Derivative [Line Items]
Derivatives not designated as hedging instruments	7,730	0	0
Not Designated as Hedging Instrument [Member] \| Income from Mortgage Banking Activities [Member] \| Forward Loan Sale Commitments [Member]
Derivative [Line Items]
Derivatives not designated as hedging instruments	$ 426	$ 0	$ 0

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5618551-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (a),(c),(d),(e)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

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- Definition

Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

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- Definition

Amount of realized and unrealized loss of derivative instruments not designated or qualifying as hedging instruments.

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- Definition

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