INVESTMENTS - Amortized Cost and Estimated Fair Values of Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Available-for-sale debt securities:
Total available-for-sale debt securities	$ 1,326,330	$ 1,466,350
Gross Unrealized Gains	604	14,966
Gross Unrealized Losses	(66,989)	(15,420)
Total available-for-sale debt securities	1,259,945	1,465,896
Held-to-maturity debt securities:
Total held-to-maturity debt securities	285,339	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(9,505)	0
Total held-to-maturity debt securities	275,834	0
Total debt securities
Amortized Cost	1,611,669	1,466,350
Gross Unrealized Gains	604	14,966
Gross Unrealized Losses	(76,494)	(15,420)
Estimated Fair Value	1,535,779	1,465,896
U.S. treasuries and government agencies
Available-for-sale debt securities:
Total available-for-sale debt securities	109,364	68,487
Gross Unrealized Gains	26	202
Gross Unrealized Losses	(3,892)	(150)
Total available-for-sale debt securities	105,498	68,539
State and municipal
Available-for-sale debt securities:
Total available-for-sale debt securities	347,877	323,286
Gross Unrealized Gains	274	6,561
Gross Unrealized Losses	(26,298)	(3,445)
Total available-for-sale debt securities	321,853	326,402
Mortgage-backed and asset-backed
Available-for-sale debt securities:
Total available-for-sale debt securities	869,089	1,074,577
Gross Unrealized Gains	304	8,203
Gross Unrealized Losses	(36,799)	(11,825)
Total available-for-sale debt securities	832,594	1,070,955
Held-to-maturity debt securities:
Total held-to-maturity debt securities	285,339	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(9,505)	0
Total held-to-maturity debt securities	$ 275,834	$ 0