Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) Customer	Sep. 30, 2016 Customer	Sep. 30, 2017 USD ($) Customer	Sep. 30, 2016 Customer	Dec. 31, 2016 USD ($)
Short-term investments	$ 24,029,000		$ 24,029,000		$ 0
Money Market Funds and U.S. Government Securities
Cash and cash equivalents fair value disclosure	$ 19,500,000		$ 19,500,000
Customer Concentration Risk | Revenue
Number of customers above 10% threshold | Customer	0	0	0	0
Customer Concentration Risk | Accounts Receivable
Number of customers above 10% threshold | Customer	0	0	0	0
Maximum
Cash and cash equivalent, FDIC insured amount	$ 250,000		$ 250,000