REGULATORY CAPITAL - Summary of Capital Amounts, Tier 1 Risk Based and Tier 1 Leveraged Ratios (Detail) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity Tier 1 capital (to risk weighted assets), Actual Amount	$ 2,089,260	$ 1,803,601
Tier 1 capital (to risk weighted assets), Actual Amount	2,171,461	1,941,394
Total capital (to risk weighted assets), Actual Amount	2,466,429	2,219,984
Tier 1 capital (to average assets), Actual Amount	$ 2,171,461	$ 1,941,394
Common equity Tier 1 (to risk weighted assets), Actual Ratio	12.999%	12.087%
Tier 1 capital (to risk weighted assets), Actual Ratio	0.13510	0.13011
Total capital (to risk weighted assets), Actual Ratio	0.15345	0.14878
Tier 1 capital (to average assets), Actual Ratio	0.09034	0.08694
Common equity Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	$ 723,277	$ 671,841
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	964,369	895,308
Total capital (to risk weighted assets), For Capital Adequacy Purposes Amount	1,285,825	1,193,744
Tier 1 capital (to average assets), For Capital Adequacy Purposes Amount	$ 961,444	$ 893,254
Common equity Tier 1 (to risk weighted assets), For Capital Adequacy Purposes Ratio	4.50%	4.50%
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Ratio	0.06000	0.06000
Total capital (to risk weighted assets), For Capital Adequacy Purposes Ratio	0.08000	0.08000
Tier 1 capital (to average assets), For Capital Adequacy Purposes Ratio	0.04000	0.04000
Common equity Tier 1 (to risk weighted assets), for Basel III amount	$ 1,125,097	$ 1,044,526
Tier 1 (to risk weighted assets) Required for Basel III amount	1,366,189	1,268,353
Total capital (to risk weighted assets), for Basel III amount	1,687,646	1,566,789
Tier 1 (to risk average assets), for Basel III amount	$ 961,444	$ 893,254
Common equity Tier 1 (to risk weighted assets), for Basel III ratio	7.00%	7.00%
Tier 1 capital (to risk weighted assets), for Basel III ratio	8.50%	8.50%
Total capital (to risk weighted assets), for Basel III ratio	10.50%	10.50%
Tier 1 capital (to average assets), for Basel III ratio	4.00%	4.00%
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Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity Tier 1 capital (to risk weighted assets), Actual Amount	$ 2,121,804	$ 1,930,951
Tier 1 capital (to risk weighted assets), Actual Amount	2,121,804	1,930,951
Total capital (to risk weighted assets), Actual Amount	2,343,688	2,136,594
Tier 1 capital (to average assets), Actual Amount	$ 2,121,804	$ 1,930,951
Common equity Tier 1 (to risk weighted assets), Actual Ratio	13.222%	12.955%
Tier 1 capital (to risk weighted assets), Actual Ratio	0.13222	0.12955
Total capital (to risk weighted assets), Actual Ratio	0.14604	0.14335
Tier 1 capital (to average assets), Actual Ratio	0.08835	0.08652
Common equity Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	$ 722,164	$ 670,719
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	962,885	894,292
Total capital (to risk weighted assets), For Capital Adequacy Purposes Amount	1,283,846	1,192,390
Tier 1 capital (to average assets), For Capital Adequacy Purposes Amount	$ 960,668	$ 892,755
Common equity Tier 1 (to risk weighted assets), For Capital Adequacy Purposes Ratio	4.50%	4.50%
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Ratio	0.06000	0.06000
Total capital (to risk weighted assets), For Capital Adequacy Purposes Ratio	0.08000	0.08000
Tier 1 capital (to average assets), For Capital Adequacy Purposes Ratio	0.04000	0.04000
Common equity Tier 1 Capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 1,043,125	$ 968,817
Tier 1 capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	1,283,846	1,192,390
Total capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	1,604,808	1,490,487
Tier 1 capital (to average assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 1,200,835	$ 1,115,944
Common equity Tier 1 (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio	6.50%	6.50%
Tier 1 capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio	0.08000	0.08000
Total capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio	0.10000	0.10000
Tier 1 capital (to average assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio	0.05000	0.05000
Common equity Tier 1 (to risk weighted assets), for Basel III amount	$ 1,123,365	$ 1,043,341
Tier 1 (to risk weighted assets) Required for Basel III amount	1,364,087	1,266,914
Total capital (to risk weighted assets), for Basel III amount	1,685,048	1,565,012
Tier 1 (to risk average assets), for Basel III amount	$ 960,668	$ 892,755
Common equity Tier 1 (to risk weighted assets), for Basel III ratio	7.00%	7.00%
Tier 1 capital (to risk weighted assets), for Basel III ratio	8.50%	8.50%
Total capital (to risk weighted assets), for Basel III ratio	10.50%	10.50%
Tier 1 capital (to average assets), for Basel III ratio	4.00%	4.00%