Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016 USD ($) Claim Segment	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments | Segment	1
Capitalized deferred issuance costs				$ 4,300,000
Series A [Member]
Summary Of Significant Accounting Policies [Line Items]
Preferred stock, liquidation preference		$ 0
Guarantees and Indemnifications [Member]
Summary Of Significant Accounting Policies [Line Items]
Indemnification obligations, claims outstanding | Claim	0
Indemnification obligations claims, reserves established	$ 0
Cost-Sharing Collaborations [Member]
Summary Of Significant Accounting Policies [Line Items]
External costs related to cost-sharing collaborations	500,000	0	$ 0
Cost-sharing collaborations recorded as a reduction to research and development expense	$ (300,000)
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives	P3Y
Percentage of income tax contingency realized	50.00%
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives	P5Y
Initial Public Offering [Member]
Summary Of Significant Accounting Policies [Line Items]
Capitalized deferred issuance costs	$ 0	$ 1,600,000