Quarterly report pursuant to Section 13 or 15(d)

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 6 Months Ended 12 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Income Tax Disclosure [Abstract]          
Income tax expense at the federal statutory rate $ 6,368 $ 8,967 $ 11,474 $ 15,793  
State income tax expense, net of federal benefit 1,415 973 2,511 1,741  
Effect of foreign operations (12) 25 (20) 47  
Windfall tax benefits, net related to stock-based compensation (28) 0 (245) (156)  
Change in valuation allowance 74 62 121 116  
Permanent items and other 338 25 616 13  
Provision for income taxes, amount $ 8,155 $ 10,052 $ 14,457 $ 17,554  
Income tax expense at the federal statutory rate 21.00% 35.00% 21.00% 35.00% 35.00%
State income tax expense, net of federal benefit 4.70% 3.80% 4.60% 3.90%  
Effect of foreign operations 0.00% 0.10% 0.00% 0.10%  
Windfall tax benefits, net related to stock-based compensation (0.10%) 0.00% (0.50%) (0.40%)  
Change in valuation allowance 0.20% 0.20% 0.20% 0.30%  
Permanent items and other 1.10% 0.10% 1.10% 0.00%  
Provision for income taxes, rate 26.90% 39.20% 26.40% 38.90%