Property and Equipment Net - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Total property and equipment	$ 17,254	$ 9,948
Accumulated depreciation and amortization	(3,277)	(624)
Property and equipment, net	13,977	9,324
Computer Equipment and Software [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	1,481	1,038
Lab Equipment [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	8,561	2,780
Furniture and Fixtures [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	1,384	1,213
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Total property and equipment	$ 5,828	$ 4,917