Income Taxes - Summary of Valuation Allowance for Deferred Tax Assets (Details) - USD ($) $ in Thousands |
12 Months Ended | ||
---|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
Valuation Allowance [Abstract] | |||
Balance at beginning of year | $ 44,248 | $ 44,861 | $ 38,565 |
Additions | 21,638 | 6,296 | |
Deductions | 613 | ||
Balance at end of year | $ 65,886 | $ 44,248 | $ 44,861 |