INVESTMENTS - Gross Unrealized Losses and Fair Value by Length of Time of Available-For-Sale Securities (Detail) $ in Thousands	Sep. 30, 2021 USD ($) security	Dec. 31, 2020 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Number of Securities | security	98	34
Fair Value
Less Than 12 Months	$ 547,099	$ 92,868
12 Months or More	30,247	76,879
Total	577,346	169,747
Unrealized Losses
Less Than 12 Months	6,966	367
12 Months or More	1,366	693
Total	$ 8,332	$ 1,060
U.S. treasuries and government agencies
Debt Securities, Available-for-sale [Line Items]
Number of Securities | security	2	2
Fair Value
Less Than 12 Months	$ 10,967	$ 25,369
12 Months or More	0	0
Total	10,967	25,369
Unrealized Losses
Less Than 12 Months	8	2
12 Months or More	0	0
Total	$ 8	$ 2
State and municipal
Debt Securities, Available-for-sale [Line Items]
Number of Securities | security	36	8
Fair Value
Less Than 12 Months	$ 90,013	$ 22,753
12 Months or More	14,643	0
Total	104,656	22,753
Unrealized Losses
Less Than 12 Months	2,169	211
12 Months or More	908	0
Total	$ 3,077	$ 211
Mortgage-backed and asset-backed
Debt Securities, Available-for-sale [Line Items]
Number of Securities | security	60	24
Fair Value
Less Than 12 Months	$ 446,119	$ 44,746
12 Months or More	15,604	76,879
Total	461,723	121,625
Unrealized Losses
Less Than 12 Months	4,789	154
12 Months or More	458	693
Total	$ 5,247	$ 847