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% |