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Income Taxes - Reconciliation of U.S. Federal Statutory Tax Rate to Company's Effective Tax Rate (Detail) | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Income Tax Disclosure [Abstract] |  |  |  |
U.S. federal statutory rate | 21.00% | 21.00% | 21.00% | 35.00%
State taxes, net of federal benefit | 4.70% | 5.00% | 5.00% |
State deferred tax apportionment change, net of federal benefit | (1.60%) | 0.10% | 0.70% |
Valuation allowance | 0.00% | 0.00% | (0.50%) |
Share-based compensation | (1.40%) | (1.60%) | (1.90%) |
Enactment of the Tax Cuts and Jobs Act | (0.30%) | (0.10%) | (0.10%) |
Other | 0.40% | 0.60% | 0.00% |
Effective Income Tax Rate | 22.80% | 25.00% | 24.20% |

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