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Employee Benefit Plans - Additional Information (Detail) - USD ($)
1 Months Ended 12 Months Ended
Oct. 31, 2017
Dec. 31, 2017
Defined Contribution Plan Disclosure [Line Items]    
Matching contributions made   $ 0
Severance Benefit Plan [Member]    
Defined Contribution Plan Disclosure [Line Items]    
Vesting period of shares granted to retained employees 2 years 2 years
Cash retention bonus percentage of each retained employees then current base salary 50.00% 50.00%
Required additional continuing employment period for retained employees 12 months 12 months
Severance Benefit Plan [Member] | Restricted stock units [Member]    
Defined Contribution Plan Disclosure [Line Items]    
Approximate number of shares granted to retained employees 907,000 907,000