Fair Value Measurements - Schedule of Reconciliation of Debt Securities (Detail) - Debt Securities [Member] - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Thousands |
9 Months Ended | |
---|---|---|
Sep. 30, 2018 |
Sep. 30, 2017 |
|
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] | ||
Debt security, Beginning balance | $ 16,050 | $ 12,220 |
Accrued interest income | 0 | 0 |
Gains or losses recorded for the period | ||
Recognized in net income | 0 | (5,585) |
Recognized in other comprehensive income | 3,200 | 2,365 |
Debt security, Ending balance | $ 19,250 | $ 9,000 |