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Income Taxes - Schedule of Differences Between Effective Rate and United States Federal Income Tax Statutory Rate (Detail)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Income Tax Disclosure [Abstract]      
Tax at statutory rate 21.00% 35.00% 35.00%
State income tax, net of federal benefit 4.80% 3.33% 2.94%
Non-deductible expenses 0.44% 0.49% 0.43%
Change in accrual estimates relating to uncertain tax positions 0.05% 0.02% (2.11%)
Change in valuation allowance     0.48%
Other, net 1.20% 0.16% 0.06%
Change in tax law (0.32%) (17.06%)  
Income tax provision 27.17% 21.94% 36.80%