Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands  | 
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2018  | 
Jun. 30, 2017  | 
Jun. 30, 2018  | 
Jun. 30, 2017  | 
|
| Income Tax Disclosure [Line Items] | ||||
| Income Tax Expense (Benefit) | $ 1,438 | $ 0 | $ 1,438 | $ 0 | 
| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
  | 
| X | ||||||||||
- Definition Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
  |