Regulatory Capital - Summary of Capital Amounts, Tier 1 Risk Based and Tier 1 Leveraged Ratios (Detail) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity Tier 1 capital (to risk weighted assets), Actual Amount	$ 1,510,392	$ 1,470,837
Tier 1 capital (to risk weighted assets), Actual Amount	1,648,185	1,608,630
Total capital (to risk weighted assets), Actual Amount	1,928,747	1,862,089
Tier 1 capital (to average assets), Actual Amount	$ 1,648,185	$ 1,608,630
Common equity Tier 1 (to risk weighted assets), Actual Ratio	10.312%	9.637%
Tier 1 capital (to risk weighted assets), Actual Ratio	0.11253	0.10539
Total capital (to risk weighted assets), Actual Ratio	0.13168	0.12200
Tier 1 capital (to average assets), Actual Ratio	0.07529	0.07664
Common equity Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	$ 659,119	$ 686,838
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	878,825	915,784
Total capital (to risk weighted assets), For Capital Adequacy Purposes Amount	1,171,767	1,221,045
Tier 1 capital (to average assets), For Capital Adequacy Purposes Amount	$ 875,660	$ 839,547
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	$ 1,025,296	$ 1,068,415
Tier 1 (to risk weighted assets) Required for Basel III amount	1,245,003	1,297,361
Total capital (to risk weighted assets), for Basel III amount	1,537,944	1,602,622
Tier 1 (to risk average assets), for Basel III amount	$ 875,660	$ 839,547
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	$ 1,749,287	$ 1,708,598
Tier 1 capital (to risk weighted assets), Actual Amount	1,749,287	1,708,598
Total capital (to risk weighted assets), Actual Amount	1,957,174	1,889,472
Tier 1 capital (to average assets), Actual Amount	$ 1,749,287	$ 1,708,598
Common equity Tier 1 (to risk weighted assets), Actual Ratio	11.959%	11.213%
Tier 1 capital (to risk weighted assets), Actual Ratio	0.11959	0.11213
Total capital (to risk weighted assets), Actual Ratio	0.13380	0.12400
Tier 1 capital (to average assets), Actual Ratio	0.08000	0.08150
Common equity Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	$ 658,243	$ 685,694
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	877,658	914,259
Total capital (to risk weighted assets), For Capital Adequacy Purposes Amount	1,170,210	1,219,012
Tier 1 capital (to average assets), For Capital Adequacy Purposes Amount	$ 874,612	$ 838,611
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	$ 950,796	$ 990,447
Tier 1 capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	1,170,210	1,219,012
Total capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	1,462,763	1,523,765
Tier 1 capital (to average assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 1,093,266	$ 1,048,264
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	$ 1,023,934	$ 1,066,636
Tier 1 (to risk weighted assets) Required for Basel III amount	1,243,348	1,295,201
Total capital (to risk weighted assets), for Basel III amount	1,535,901	1,599,954
Tier 1 (to risk average assets), for Basel III amount	$ 874,612	$ 838,611
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%