ACCUMULATED OTHER COMPREHENSIVE INCOME/ (LOSS) - Net Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	$ 1,483,768	$ 1,519,679	$ 1,469,955
Period change, net of tax	34,620	(123,412)	(27,244)
Balance at end of period	1,588,142	1,483,768	1,519,679
Total
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	(131,951)	(8,539)	18,705
Period change, net of tax	34,620	(123,412)	(27,244)
Balance at end of period	(97,331)	(131,951)	(8,539)
Unrealized Gains/ (Losses) on Investments Available-for-Sale
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	(113,513)	(336)	28,175
Period change, net of tax	25,344	(113,177)	(28,511)
Balance at end of period	(88,169)	(113,513)	(336)
Defined Benefit Pension Plan
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	(8,002)	(8,203)	(9,470)
Period change, net of tax	8,002	201	1,267
Balance at end of period	0	(8,002)	(8,203)
Unrealized Losses on Debt Securities Transferred from Available-for-Sale to Held-to-Maturity
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at beginning of period	(10,436)	0	0
Period change, net of tax	1,274	(10,436)	0
Balance at end of period	$ (9,162)	$ (10,436)	$ 0