Income Taxes - Summary of Deferred Tax Asset Valuation Allowance (Detail) - Valuation Allowance of Deferred Tax Assets - USD ($) $ in Thousands |
12 Months Ended | ||
---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
Valuation And Qualifying Accounts Disclosure [Line Items] | |||
Beginning balance | $ 17,807 | $ 21,052 | $ 21,232 |
Additions charged to cost and expenses | 324 | 1,862 | |
Deductions | (6,556) | (5,107) | (180) |
Ending balance | $ 11,575 | $ 17,807 | $ 21,052 |