INVESTMENTS - Estimated fair values of debt securities available-for-sale by contractual maturity (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Fair Value
Total available-for-sale debt securities	$ 1,441,026	$ 1,348,021
Amortized Cost
Total available-for-sale debt securities	1,422,259	1,310,159
U.S. treasuries and government agencies
Fair Value
One year or less	39,811	33,963
One to five years	8,094	9,334
Five to ten years	0	0
After ten years	0	0
Total available-for-sale debt securities	47,905	43,297
Amortized Cost
One year or less	39,650	33,833
One to five years	7,911	8,917
Five to ten years	0	0
After ten years	0	0
Total available-for-sale debt securities	47,561	42,750
State and municipal
Fair Value
One year or less	14,374	16,581
One to five years	30,716	44,910
Five to ten years	49,123	59,059
After ten years	265,255	269,817
Total available-for-sale debt securities	359,468	390,367
Amortized Cost
One year or less	14,205	16,458
One to five years	29,725	43,857
Five to ten years	47,307	56,130
After ten years	260,001	260,663
Total available-for-sale debt securities	351,238	377,108
Mortgage-backed and asset-backed
Fair Value
One year or less	5,525	1
One to five years	16,032	21,637
Five to ten years	85,595	74,142
After ten years	919,029	808,652
Total available-for-sale debt securities	1,026,181	904,432
Amortized Cost
One year or less	5,459	1
One to five years	15,789	21,229
Five to ten years	83,831	72,481
After ten years	911,381	787,490
Total available-for-sale debt securities	1,016,460	881,201
Corporate debt
Fair Value
One year or less	0	0
One to five years	0	2,318
Five to ten years	7,472	7,607
After ten years	0	0
Total available-for-sale debt securities	7,472	9,925
Amortized Cost
One year or less	0	0
One to five years	0	2,100
Five to ten years	7,000	7,000
After ten years	0	0
Total available-for-sale debt securities	$ 7,000	$ 9,100