INVESTMENTS - Amortized Cost and Estimated Fair Values of Investments Available-for-sale (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Total available-for-sale debt securities	$ 1,418,931	$ 1,310,159
Gross Unrealized Gains	24,178	38,922
Gross Unrealized Losses	15,229	1,060
Total available-for-sale debt securities	1,427,880	1,348,021
U.S. treasuries and government agencies
Debt Securities, Available-for-sale [Line Items]
Total available-for-sale debt securities	47,641	42,750
Gross Unrealized Gains	447	549
Gross Unrealized Losses	2	2
Total available-for-sale debt securities	48,086	43,297
State and municipal
Debt Securities, Available-for-sale [Line Items]
Total available-for-sale debt securities	362,815	377,108
Gross Unrealized Gains	7,926	13,470
Gross Unrealized Losses	4,709	211
Total available-for-sale debt securities	366,032	390,367
Mortgage-backed and asset-backed
Debt Securities, Available-for-sale [Line Items]
Total available-for-sale debt securities	1,001,475	881,201
Gross Unrealized Gains	15,222	24,078
Gross Unrealized Losses	10,518	847
Total available-for-sale debt securities	1,006,179	904,432
Corporate debt
Debt Securities, Available-for-sale [Line Items]
Total available-for-sale debt securities	7,000	9,100
Gross Unrealized Gains	583	825
Gross Unrealized Losses	0	0
Total available-for-sale debt securities	$ 7,583	$ 9,925

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on 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, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on 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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Amortized cost 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 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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