Investment Securities - Amortized Cost and Estimated Fair Values of Investments Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Debt Securities Available for Sale, Amortized Cost	$ 1,132,705	$ 1,136,010
Debt Securities Available for Sale, Gross Unrealized Gains	8,021	1,235
Debt Securities Available for Sale, Gross Unrealized Losses	(6,732)	(22,209)
Debt Securities Available for Sale, Estimated Fair Value	1,133,994	1,115,036
Debt Securities Held to Maturity, Amortized Cost	412,524	444,936
Debt Securities Held to Maturity, Gross Unrealized Gains	3,951	409
Debt Securities Held to Maturity, Gross Unrealized Losses	(1,199)	(7,975)
Debt Securities Held to Maturity, Estimated Fair Value	415,276	437,370
Obligations of U.S. Government Agencies [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities Available for Sale, Amortized Cost	627,996	647,288
Debt Securities Available for Sale, Gross Unrealized Gains	5,193	771
Debt Securities Available for Sale, Gross Unrealized Losses	(2,278)	(18,078)
Debt Securities Available for Sale, Estimated Fair Value	630,911	629,981
Debt Securities Held to Maturity, Amortized Cost	398,714	430,343
Debt Securities Held to Maturity, Gross Unrealized Gains	3,661	327
Debt Securities Held to Maturity, Gross Unrealized Losses	(1,199)	(7,745)
Debt Securities Held to Maturity, Estimated Fair Value	401,176	422,925
Obligations of States and Political Subdivisions [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities Available for Sale, Amortized Cost	123,626	128,890
Debt Securities Available for Sale, Gross Unrealized Gains	2,462	294
Debt Securities Available for Sale, Gross Unrealized Losses	(108)	(3,112)
Debt Securities Available for Sale, Estimated Fair Value	125,980	126,072
Debt Securities Held to Maturity, Amortized Cost	13,810	14,593
Debt Securities Held to Maturity, Gross Unrealized Gains	290	82
Debt Securities Held to Maturity, Gross Unrealized Losses		(230)
Debt Securities Held to Maturity, Estimated Fair Value	14,100	14,445
Corporate Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities Available for Sale, Amortized Cost	4,407	4,381
Debt Securities Available for Sale, Gross Unrealized Gains	114	97
Debt Securities Available for Sale, Estimated Fair Value	4,521	4,478
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities Available for Sale, Amortized Cost	376,676	355,451
Debt Securities Available for Sale, Gross Unrealized Gains	252	73
Debt Securities Available for Sale, Gross Unrealized Losses	(4,346)	(1,019)
Debt Securities Available for Sale, Estimated Fair Value	$ 372,582	$ 354,505

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

No definition available.

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- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

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- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

No definition available.

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

No definition available.

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Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (c)
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Amount, before other-than-temporary impairment (OTTI) accretion, of investment in debt securities measured at amortized cost (held-to-maturity).

+ References

No definition available.

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- Definition

Fair value of investment in debt security measured at amortized cost (held-to-maturity).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
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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.

+ References

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