Regulatory Capital Requirements - Actual Capital Amounts and Ratios and FDIC Minimum Capital Adequacy Requirements (Detail) $ in Thousands	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
FRB
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 leverage capital, Actual Amount	$ 1,252,925	$ 1,157,505
Tier 1 leverage capital, Actual Ratio	0.0945	0.0930
Tier 1 leverage capital, minimum capital adequacy requirements, Amount	$ 530,602	$ 497,794
Tier 1 leverage capital, minimum capital adequacy requirements, Ratio	0.0400	0.0400
Tier 1 leverage capital, minimum capital adequacy requirements with capital conservation buffer, Amount	$ 530,602	$ 497,794
Tier 1 leverage capital, minimum capital adequacy requirements with capital conservation buffer, Ratio	4.00%	4.00%
Tier 1 leverage capital, To be well-capitalized under prompt corrective action provisions, Amount	$ 663,252	$ 622,243
Tier 1 leverage capital, To be well-capitalized under prompt corrective action provisions, Ratio	0.0500	0.0500
Common equity Tier 1 risk-based capital, Actual Amount	$ 1,240,038	$ 1,144,618
Common equity Tier 1 risk-based capital, Actual Ratio	11.47%	10.46%
Common equity Tier 1 risk-based capital, minimum capital adequacy requirement, Amount	$ 486,382	$ 492,359
Common equity Tier 1 risk-based capital, minimum capital adequacy requirement, Ratio	4.50%	4.50%
Common equity Tier 1 risk-based capital, minimum capital adequacy requirement with capital conversation buffer, Amount	$ 756,595	$ 765,892
Common equity Tier 1 risk-based capital, minimum capital adequacy requirement with capital conversation buffer, Ratio	7.00%	7.00%
Common equity Tier 1 risk-based capital, To be well-capitalized under prompt corrective action provisions, Amount	$ 702,552	$ 711,185
Common equity Tier 1 risk-based capital, To be well-capitalized under prompt corrective action provisions, Ratio	6.50%	6.50%
Tier 1 risk-based capital, Actual Amount	$ 1,252,925	$ 1,157,505
Tier 1 risk-based capital, Actual Ratio	0.1159	0.1058
Tier 1 risk-based capital, minimum capital adequacy requirements, Amount	$ 648,510	$ 656,478
Tier 1 risk-based capital, minimum capital adequacy requirements, Ratio	0.0600	0.0600
Tier 1 risk-based capital, minimum capital adequacy requirements with capital conversation buffer, Amount	$ 918,722	$ 930,011
Tier 1 risk-based capital, minimum capital adequacy requirements with capital conversation buffer, Ratio	8.50%	8.50%
Tier 1 risk-based capital, To be well-capitalized under prompt corrective action provisions, Amount	$ 864,680	$ 875,305
Tier 1 risk-based capital, To be well-capitalized under prompt corrective action provisions, Ratio	0.0800	0.0800
Total risk-based capital, Actual Amount	$ 1,324,032	$ 1,306,494
Total risk-based capital, Actual Ratio	0.1225	0.1194
Total risk-based capital, minimum capital adequacy requirements, Amount	$ 864,680	$ 875,305
Total risk-based capital, minimum capital adequacy requirements, Ratio	0.0800	0.0800
Total risk-based capital, minimum capital adequacy requirements with capital conversation buffer, Amount	$ 1,134,892	$ 1,148,837
Total risk-based capital, minimum capital adequacy requirements with capital conversation buffer, Ratio	10.50%	10.50%
Total risk-based capital, to be well-capitalized under prompt corrective action provisions, Amount	$ 1,080,850	$ 1,094,131
Total risk-based capital, to be well-capitalized under prompt corrective action provisions, Ratio	0.1000	0.1000
FDIC
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 leverage capital, Actual Amount	$ 1,174,495	$ 1,086,589
Tier 1 leverage capital, Actual Ratio	0.0886	0.0875
Tier 1 leverage capital, minimum capital adequacy requirements, Amount	$ 530,275	$ 496,908
Tier 1 leverage capital, minimum capital adequacy requirements, Ratio	0.0400	0.0400
Tier 1 leverage capital, minimum capital adequacy requirements with capital conservation buffer, Amount	$ 530,275	$ 496,908
Tier 1 leverage capital, minimum capital adequacy requirements with capital conservation buffer, Ratio	4.00%	4.00%
Tier 1 leverage capital, To be well-capitalized under prompt corrective action provisions, Amount	$ 662,844	$ 621,135
Tier 1 leverage capital, To be well-capitalized under prompt corrective action provisions, Ratio	0.05	0.0500
Common equity Tier 1 risk-based capital, Actual Amount	$ 1,174,495	$ 1,086,589
Common equity Tier 1 risk-based capital, Actual Ratio	10.87%	9.96%
Common equity Tier 1 risk-based capital, minimum capital adequacy requirement, Amount	$ 486,122	$ 491,135
Common equity Tier 1 risk-based capital, minimum capital adequacy requirement, Ratio	4.50%	4.50%
Common equity Tier 1 risk-based capital, minimum capital adequacy requirement with capital conversation buffer, Amount	$ 756,190	$ 763,988
Common equity Tier 1 risk-based capital, minimum capital adequacy requirement with capital conversation buffer, Ratio	7.00%	7.00%
Common equity Tier 1 risk-based capital, To be well-capitalized under prompt corrective action provisions, Amount	$ 702,177	$ 709,417
Common equity Tier 1 risk-based capital, To be well-capitalized under prompt corrective action provisions, Ratio	6.50%	6.50%
Tier 1 risk-based capital, Actual Amount	$ 1,174,495	$ 1,086,589
Tier 1 risk-based capital, Actual Ratio	0.1087	0.0996
Tier 1 risk-based capital, minimum capital adequacy requirements, Amount	$ 648,163	$ 654,847
Tier 1 risk-based capital, minimum capital adequacy requirements, Ratio	0.06	0.0600
Tier 1 risk-based capital, minimum capital adequacy requirements with capital conversation buffer, Amount	$ 918,231	$ 927,700
Tier 1 risk-based capital, minimum capital adequacy requirements with capital conversation buffer, Ratio	8.50%	8.50%
Tier 1 risk-based capital, To be well-capitalized under prompt corrective action provisions, Amount	$ 864,217	$ 873,129
Tier 1 risk-based capital, To be well-capitalized under prompt corrective action provisions, Ratio	0.0800	0.0800
Total risk-based capital, Actual Amount	$ 1,245,602	$ 1,223,469
Total risk-based capital, Actual Ratio	0.1153	0.1121
Total risk-based capital, minimum capital adequacy requirements, Amount	$ 864,217	$ 873,129
Total risk-based capital, minimum capital adequacy requirements, Ratio	0.08	0.0800
Total risk-based capital, minimum capital adequacy requirements with capital conversation buffer, Amount	$ 1,134,285	$ 1,145,982
Total risk-based capital, minimum capital adequacy requirements with capital conversation buffer, Ratio	10.50%	10.50%
Total risk-based capital, to be well-capitalized under prompt corrective action provisions, Amount	$ 1,080,272	$ 1,091,411
Total risk-based capital, to be well-capitalized under prompt corrective action provisions, Ratio	0.10	0.1000