Annual report pursuant to Section 13 and 15(d)

Defined Contribution Plan - Additional Information (Detail)

v3.8.0.1
Defined Contribution Plan - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Defined Contribution Benefit Plans [Line Items]      
Defined contribution plan matching contribution, Description Under the plan, we provide a dollar for dollar match for the first 4% of the employee's contributions and a $0.50 per dollar match for the next 2% of employee contributions.    
First 4% of Employee's Contribution [Member]      
Defined Contribution Benefit Plans [Line Items]      
Defined contribution plan employer's matching contribution, Percentage of match 100.00%    
Next 2% of Employee's Contribution [Member]      
Defined Contribution Benefit Plans [Line Items]      
Defined contribution plan employer's matching contribution, Percentage of match 50.00%    
Maximum [Member]      
Defined Contribution Benefit Plans [Line Items]      
Contribution plan cost $ 1,000,000 $ 1,000,000 $ 1,000,000