Cash, Cash Equivalents and Marketable Securities - Additional Information (Detail) - USD ($) $ in Thousands |
12 Months Ended | |
---|---|---|
Dec. 31, 2016 |
Sep. 30, 2017 |
|
Cash, cash equivalents and marketable securities [Line Items] | ||
Marketable securities | $ 19,547 | $ 0 |
Long-term marketable securities, minimum original maturity term | 1 year | |
Long-term marketable securities | $ 0 | |
Minimum | ||
Cash, cash equivalents and marketable securities [Line Items] | ||
Short-term marketable securities, minimum original maturity term | 90 days |