Basis of presentation and summary of significant accounting policies - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Significant Accounting Policies [Line Items]
Recognition of right-of-use assets	$ 770
Recognition of lease liabilities	1,003
Accumulated deficit	$ (299,529)		$ (230,087)
Intangible asset, useful life	3 years
Accounting Standards Update 2016-02 [Member]
Significant Accounting Policies [Line Items]
Recognition of right-of-use assets		$ 200
Recognition of lease liabilities		500
Derecognition of deferred rent liability		$ 300