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Income Taxes - Components of Provision for Income Taxes and Income before Provision for Income Taxes (Detail)

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Income Taxes - Components of Provision for Income Taxes and Income before Provision for Income Taxes (Detail) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Income Tax Disclosure [Abstract]      
Income tax expense at the federal statutory rate $ 5,106 $ 6,826  
State income tax expense, net of federal benefit 1,097 768  
Effect of foreign operations 32 76  
Windfall tax benefits, net related to stock-based compensation (217) (156)  
Permanent items and other 284 (12)  
Provision for income taxes, amount $ 6,302 $ 7,502  
Income tax expense at the federal statutory rate 21.00% 35.00% 35.00%
State income tax expense, net of federal benefit 4.50% 3.90%  
Effect of foreign operations 0.10% 0.40%  
Windfall tax benefits, net related to stock-based compensation (0.90%) (0.70%)  
Permanent items and other 1.20% (0.10%)  
Provision for income taxes, rate 25.90% 38.50%