Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) |
9 Months Ended | |
---|---|---|
Sep. 30, 2017 |
Dec. 31, 2016 |
|
Summary Of Significant Accounting Policies [Line Items] | ||
Transfers between Levels 1, 2 and 3 | $ 0 | $ 0 |
Sale of available for sale securities | 0 | |
Aggregate fair value of available for sale securities held for less than twelve months | 1,800,000 | |
Significant Unobservable Inputs (Level 3) [Member] | ||
Summary Of Significant Accounting Policies [Line Items] | ||
Assets, fair value disclosure, recurring | 0 | 0 |
Liabilities, fair value disclosure, recurring | $ 0 | $ 0 |