Supplemental Disclosures - Schedules of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Payables And Accruals [Abstract]
Accrued personnel costs	$ 3,338	$ 1,371
Accrued external research and development expenses	3,005	835
Accrued purchases of property and equipment	844
Accrued external general and administrative expenses	672	559
Accrued sublicense fees and royalties on reagent sales		260
Other accrued expenses and current liabilities	267	173
Accrued expenses and other current liabilities	$ 8,126	$ 3,198