Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)		1 Months Ended		12 Months Ended
	Jul. 02, 2015	Feb. 29, 2016	Jan. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Line Items]
Maximum maturity days for cash equivalents				90 days
Restricted cash				$ 1,400,000	$ 1,539,000
Deferred offering costs				0	$ 0
Reclassification of deferred offering costs to additional paid in capital	$ 3,748,000
Impairment losses on long lived assets				$ 0
Minimum percentage of likelihood of tax benefit being realized upon settlement				50.00%
Nestlé Health Science [Member]
Accounting Policies [Line Items]
Upfront non-refundable payment		$ 120,000,000	$ 120,000,000	$ 120,000,000
Laboratory Equipment [Member]
Accounting Policies [Line Items]
Useful life of asset				5 years
Computer Equipment [Member]
Accounting Policies [Line Items]
Useful life of asset				3 years
Furniture and Office Equipment [Member]
Accounting Policies [Line Items]
Useful life of asset				3 years