Derivative Instruments and Hedging Activities - Effect of Derivative Instruments on Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gains (losses) arising during the period	$ 1,995	$ 666	$ (1,093)
Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Amount of income (loss) recognized in earnings	3,545	790	3,118
Not Designated as Hedging Instrument \| Other non-interest income \| Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
Amount of income (loss) recognized in earnings	3,409	604	2,955
Not Designated as Hedging Instrument \| Other non-interest income \| Credit contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amount of income (loss) recognized in earnings	127	171	163
Not Designated as Hedging Instrument \| Mortgage banking income \| Residential mortgage loan commitments
Derivative Instruments, Gain (Loss) [Line Items]
Amount of income (loss) recognized in earnings	9	15	0
Designated as Hedging Instrument \| Interest Rate Swap \| Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gains (losses) arising during the period	1,477	406	(629)
Amount of gain (loss) reclassified from accumulated OCI into income (effective portion)	2,917
Designated as Hedging Instrument \| Other non-interest income \| Interest Rate Swap \| Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) reclassified from accumulated OCI into income (ineffective portion)	2,822
Designated as Hedging Instrument \| Interest expense \| Interest Rate Swap \| Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) reclassified from accumulated OCI into income (effective portion)	$ 95	$ (2,634)	$ (1,946)

Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Ineffective Portion, Net

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- Definition

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

+ References

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-Publisher FASB
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-SubTopic 10
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No definition available.

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The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

+ References

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- Definition

Amount before tax of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

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