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Fair Value - Fair Value Measurement (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assumed Gain/(Loss) From Loan Sale	$ 2,153
Interest Rate Movement Effect	(4,310)
Servicing Rights Value	14,314
Security Price Change	1,280
Total Fair Value Measurement Gain/(Loss)	13,437	$ 5,824
Mortgage Banking [Member] | Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rate Lock Commitments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional or Principal Amount	864,355
Assumed Gain/(Loss) From Loan Sale	1,486
Interest Rate Movement Effect	(2,376)
Servicing Rights Value	9,920
Total Fair Value Measurement Gain/(Loss)	9,030
Mortgage Banking [Member] | Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Forward Sales Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional or Principal Amount	1,120,810
Security Price Change	1,280
Total Fair Value Measurement Gain/(Loss)	1,280
Mortgage Banking [Member] | Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mortgages Held for Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional or Principal Amount	319,817	350,558
Assumed Gain/(Loss) From Loan Sale	667
Interest Rate Movement Effect	(1,934)
Servicing Rights Value	4,394
Total Fair Value Measurement Gain/(Loss)	$ 3,127	$ 1,931

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Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
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