Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Significant Accounting Policies [Line Items]
Restricted cash	$ 425		$ 425
Lease liability	11,863	$ 3,500
Right-of-use lease assets - operating	11,372	$ 3,100
Letter of Credit [Member]
Significant Accounting Policies [Line Items]
Restricted cash	$ 400