Property and Equipment Net - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property Plant And Equipment [Line Items]
Property and equipment, net by net of accumulated depreciation	$ 9,324,000	$ 538,000
Depreciation or amortization expense	544,000	$ 80,000	$ 0
Leasehold Improvements [Member] | Office and Laboratory Facilities [Member]
Property Plant And Equipment [Line Items]
Property and equipment, net by net of accumulated depreciation	$ 4,700,000