Investments in Marketable Securities - Summary of Investments Classified As Available-For-Sale Securities (Detail) - USD ($) $ in Thousands |
Sep. 30, 2018 |
Dec. 31, 2017 |
---|---|---|
Schedule of Available-for-sale Securities [Line Items] | ||
Amortized Cost | $ 134,772 | $ 11,606 |
Gross Unrealized Losses | (116) | (19) |
Aggregate Estimated Fair Value | 134,656 | 11,587 |
Commercial paper [Member] | ||
Schedule of Available-for-sale Securities [Line Items] | ||
Amortized Cost | 3,458 | |
Aggregate Estimated Fair Value | 3,458 | |
Certificates of deposit [Member] | ||
Schedule of Available-for-sale Securities [Line Items] | ||
Amortized Cost | 249 | |
Aggregate Estimated Fair Value | 249 | |
Corporate debt securities [Member] | ||
Schedule of Available-for-sale Securities [Line Items] | ||
Amortized Cost | 131,314 | 11,357 |
Gross Unrealized Losses | (116) | (19) |
Aggregate Estimated Fair Value | $ 131,198 | $ 11,338 |