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Employee Benefit Plans - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]      
Percentage of employee's contribution to the plan up to 6% of base salary matched by the Company 100.00%    
Employer's contribution percentage 6.00%    
Employer's contribution $ 3,000,000 $ 2,500,000 $ 2,200,000
401(k) Profit Sharing Plan Two [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Employer's contribution percentage 6.00%    
Employer contribution to the plan for every $1.00 contributed by an employee $ 0.25    
Employee's contribution to the plan up to 6% of base salary by the company $ 1.00