Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended
	Apr. 02, 2019	Mar. 28, 2019	Mar. 31, 2019	Dec. 31, 2018
Class Of Stock [Line Items]
Proceeds from collaboration agreement			$ 34,910
Cash, cash equivalents and investments			13,270
Accumulated deficit			(175,979)	$ (168,493)
Private Placement [Member]
Class Of Stock [Line Items]
Aggregate gross proceeds from private placement	$ 26,000
Placement agent fees	$ 1,700
Preferred Stock [Member]
Class Of Stock [Line Items]
Proceeds from sales of stock			131,211
Common Stock [Member]
Class Of Stock [Line Items]
Net proceeds from issuance of initial public offering			$ 50,009
Common Stock [Member] | Private Placement [Member] | Purchase Agreement One [Member]
Class Of Stock [Line Items]
Stock repurchase program, number of shares to be purchased		11,838,582
Common Stock [Member] | Private Placement [Member] | Purchase Agreement Two [Member]
Class Of Stock [Line Items]
Stock repurchase program, number of shares to be purchased		1,096,741
Stock Units [Member] | Private Placement [Member] | Purchase Agreement One [Member]
Class Of Stock [Line Items]
Issue and sale of aggregate shares		11,838,582
Sale of stock, combined price per unit		$ 2.01
Stock Units [Member] | Private Placement [Member] | Purchase Agreement Two [Member]
Class Of Stock [Line Items]
Issue and sale of aggregate shares		1,096,741
Sale of stock, combined price per unit		$ 2.01
Common Warrants [Member] | Private Placement [Member] | Purchase Agreement One [Member]
Class Of Stock [Line Items]
Aggregate shares purchase for warrants		11,838,582
Warrants exercisable, exercise price		$ 2.00
Warrants and Rights Outstanding, Term		5 years
Pre-funded Warrants [Member] | Private Placement [Member] | Purchase Agreement Two [Member]
Class Of Stock [Line Items]
Aggregate shares purchase for warrants		1,096,741
Warrants exercisable, exercise price		$ 0.01