Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Summary Of Significant Accounting Policies [Line Items]
Restricted cash, current	$ 25	$ 25
Restricted cash, non-current	568	568
490 Arsenal Way [Member] | Operating Lease Agreements [Member] | ASU No. 2016-02 [Member]
Summary Of Significant Accounting Policies [Line Items]
De-recognized building asset	7,079
De-recognition of accumulated depreciation	81
Security Deposit Related to Credit Card Accounts [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash, current	25	25
Security Deposit Related to Lease Facility [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash, non-current	$ 568	$ 568