Stockholders' Equity Common Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	Jul. 01, 2015	Jun. 26, 2015	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized				200,000,000	200,000,000	38,000,000
Common stock, par value				$ 0.001	$ 0.001	$ 0.001
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock issued and sold	8,545,138		8,545,138
Net proceeds from issuance of common stock from IPO after deducting underwriting discounts and commissions	$ 139,267
Estimated stock offering expenses	$ 3,748
Conversion of redeemable convertible preferred stock into common stock		22,866,987	22,866,987
Initial Public Offering ("IPO") [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized	200,000,000
Common stock, par value	$ 0.001
Initial Public Offering ("IPO") [Member] | Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Public offering price per share	$ 18.00
Over-Allotment Option [Member] | Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock issued and sold	1,114,583