INVESTMENTS - Amortized Cost and Estimated Fair Values of Investments Available-for-sale (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	$ 1,348,021	$ 1,073,333
Available-for-Sale Securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,310,159	1,067,954
Gross Unrealized Gains	38,922	8,984
Gross Unrealized Losses	(1,060)	(3,605)
Estimated Fair Value	1,348,021	1,073,333
Available-for-Sale Securities \| U.S. treasuries and government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	42,750	260,294
Gross Unrealized Gains	549	887
Gross Unrealized Losses	(2)	(2,686)
Estimated Fair Value	43,297	258,495
Available-for-Sale Securities \| State and municipal
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	377,108	229,309
Gross Unrealized Gains	13,470	4,377
Gross Unrealized Losses	(211)	(37)
Estimated Fair Value	390,367	233,649
Available-for-Sale Securities \| Mortgage-backed and asset-backed
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	881,201	568,373
Gross Unrealized Gains	24,078	3,268
Gross Unrealized Losses	(847)	(882)
Estimated Fair Value	904,432	570,759
Available-for-Sale Securities \| Corporate debt
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	9,100	9,100
Gross Unrealized Gains	825	452
Gross Unrealized Losses	0	0
Estimated Fair Value	9,925	9,552
Available-for-Sale Securities \| Trust preferred
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	0	310
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	0	310
Available-for-Sale Securities \| Debt Securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,310,159	1,067,386
Gross Unrealized Gains	38,922	8,984
Gross Unrealized Losses	(1,060)	(3,605)
Estimated Fair Value	1,348,021	1,072,765
Available-for-Sale Securities \| Marketable equity securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	0	568
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 0	$ 568

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.

+ Details

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- Definition

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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- Definition

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

No definition available.

+ Details

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