Derivative Financial Instruments - Schedule of Effect of Derivative Instruments on the Consolidated Statements of Income (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Other Comprehensive Income on Derivative (Effective Portion)	$ 725	$ 217	$ 6,804	$ (1,590)
Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Income on Derivative	(46)	(284)	441	(1,304)
Interest Rate Contracts [Member] \| Interest Income / (Expense) [Member] \| Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Income on Derivative	(2,786)	(196)	(4,450)	(374)
Interest Rate Contracts [Member] \| Interest Income / (Expense) [Member] \| Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Other Comprehensive Income on Derivative (Effective Portion)	725	217	6,804	(1,590)
Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	226	(1,429)	(553)	(4,962)
Interest Rate Contracts [Member] \| Other Income / (Expense) [Member] \| Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Income on Derivative	(23)	9	4	32
Fixed Rate Debt [Member] \| Interest Income / (Expense) [Member] \| Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income on Related Hedged Items	2,778	235	4,433	500
Mortgage Contracts [Member] \| Mortgage banking revenue \| Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Income on Derivative	(43)	$ (293)	394	$ (1,336)
Foreign Currency Contracts [Member] \| Other Income / (Expense) [Member] \| Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Income on Derivative	$ 20		$ 43

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

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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.

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Total amount of gain (loss) derived from fair value hedges recognized in earnings in the period.

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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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