Annual report pursuant to Section 13 and 15(d)

Employee Benefit Plan - Additional Information (Detail)

v3.8.0.1
Employee Benefit Plan - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Jan. 01, 2008
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]        
Employee contribution percentage 4.00%      
Employer matching contribution   $ 0.2 $ 0.2 $ 0.1
National Holdings [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent   75.00%