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Premises and Equipment, Net and Other Assets - Additional Information (Detail) - USD ($) | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Property Plant And Equipment [Abstract] |  |  |
Noncash construction in progress for retainage payable | $ 2,400,000 |  |
Other assets in equity interest | $ 11,100,000 |  |
Percentage of equity investment | 50.00% |  |
Low income housing tax credit investments | $ 18,100,000 | $ 20,400,000 |
Tax credits and other tax benefits recognized from LIHTC investments | 5,600,000 | 5,400,000 | $ 5,400,000
Amortization expense resulting from LIHTC investments | 4,600,000 | 4,500,000 | 4,400,000
Unfunded commitment on investments | $ 19,400,000 |  |
Percentage of qualified investment | 39.00% |  |
Period of qualified investments taken | 7 years |  |
New market tax credit investments | $ 18,500,000 | 21,800,000 |
Tax credits and other tax benefits recognized from NMTC investments | 4,000,000.0 | 4,500,000 | 1,800,000
Amortization expense resulting from NMTC investments | 3,300,000 | $ 3,700,000 | $ 1,400,000
Unfunded commitment on NMTC investments | $ 0 |  |

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