Investment Securities - Schedule of Proceeds from Sales or Calls and Realized Gain and Losses of Available-for-sale Investment Securities and Other Securities (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Debt Securities, Available-for-sale [Line Items]
Proceeds from sales of available-for-sale securities	$ 5,327	$ 98,038	$ 136,648	$ 284,315
Proceeds from calls of available-for-sale securities			316,239	337,766
Total	8,265	100,341	168,233	357,738
Realized gains on sales of available-for-sale securities		2,891	3,259	7,174
Realized losses on sales of available-for-sale securities	(74)	(36)	(1,379)	(79)
Other securities gains (losses)	216	104	313	447
Net securities gains (losses)	135	2,972	2,417	7,547
Calls [Member]
Debt Securities, Available-for-sale [Line Items]
Proceeds from calls of available-for-sale securities	2,938	2,303	31,585	73,423
Realized gains on calls of available-for-sale securities		$ 13	284	13
Realized losses on calls of available-for-sale securities	$ (7)		$ (60)	$ (8)

The gross profit realized on the call of available-for-sale debt or equity securities.

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The gross loss realized on the call of available-for-sale debt or equity securities.

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This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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Amount of unrealized and realized gain (loss) on investment in debt and equity securities.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
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Amount of unrealized and realized gain (loss) on investment in marketable security, including other-than-temporary impairment (OTTI).

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Amount of cash inflow from maturity, prepayment and call of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of cash inflow from sale, maturity, prepayment and call of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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