Regulatory Capital - Summary of Capital Amounts, Tier 1 Risk Based and Tier 1 Leveraged Ratios (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity Tier 1 capital (to risk weighted assets), Actual Amount	$ 1,447,890	$ 1,291,270
Tier 1 capital (to risk weighted assets), Actual Amount	1,585,683	1,429,063
Total capital (to risk weighted assets), Actual Amount	1,838,179	1,667,395
Tier 1 capital (to average assets), Actual Amount	$ 1,585,683	$ 1,429,063
Common equity Tier 1 (to risk weighted assets), Actual Ratio	9.845%	9.981%
Tier 1 capital (to risk weighted assets), Actual Ratio	0.10782	0.11046
Total capital (to risk weighted assets), Actual Ratio	0.12499	0.12888
Tier 1 capital (to average assets), Actual Ratio	0.07650	0.07413
Common equity Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	$ 661,804	$ 582,179
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	882,405	776,238
Total capital (to risk weighted assets), For Capital Adequacy Purposes Amount	1,176,540	1,034,984
Tier 1 capital (to average assets), For Capital Adequacy Purposes Amount	$ 829,133	$ 771,084
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	$ 1,029,472	$ 905,611
Tier 1 (to risk weighted assets) Required for Basel III amount	1,250,073	1,099,671
Total capital (to risk weighted assets), for Basel III amount	1,544,208	1,358,417
Tier 1 (to risk average assets), for Basel III amount	$ 829,133	$ 771,084
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	$ 1,676,998	$ 1,526,583
Tier 1 capital (to risk weighted assets), Actual Amount	1,676,998	1,526,583
Total capital (to risk weighted assets), Actual Amount	1,856,955	1,692,512
Tier 1 capital (to average assets), Actual Amount	$ 1,676,998	$ 1,526,583
Common equity Tier 1 (to risk weighted assets), Actual Ratio	11.42%	11.825%
Tier 1 capital (to risk weighted assets), Actual Ratio	0.11420	0.11825
Total capital (to risk weighted assets), Actual Ratio	0.12646	0.13110
Tier 1 capital (to average assets), Actual Ratio	0.08099	0.07925
Common equity Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	$ 660,807	$ 580,943
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	881,076	774,591
Total capital (to risk weighted assets), For Capital Adequacy Purposes Amount	1,174,768	1,032,788
Tier 1 capital (to average assets), For Capital Adequacy Purposes Amount	$ 828,289	$ 770,528
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	$ 954,499	$ 839,140
Tier 1 capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	1,174,768	1,032,788
Total capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	1,468,460	1,290,985
Tier 1 capital (to average assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 1,035,361	$ 963,160
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	$ 1,027,922	$ 903,689
Tier 1 (to risk weighted assets) Required for Basel III amount	1,248,191	1,097,337
Total capital (to risk weighted assets), for Basel III amount	1,541,883	1,355,534
Tier 1 (to risk average assets), for Basel III amount	$ 828,289	$ 770,528
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%