Stockholder's Equity - Schedule of Transaction Related to Stockholder's Equity (Detail) - USD ($) $ in Thousands			3 Months Ended						9 Months Ended
	Jun. 24, 2019	Apr. 30, 2018	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Beginning balance			$ 55,224	$ 34,433	$ 42,911	$ 59,916	$ 13,505	$ 21,361	$ 42,911	$ 21,361
Beginning balance, shares					35,860,114				35,860,114
Exercise of stock options			28	90	$ 25	6	97
Exercise of stock options, shares									91,327
Repurchase of common shares							(31)
Vesting of restricted stock units			(44)	(111)	(121)
Equity financing issuance costs			(50)
Issuance of warrants					421				$ 400
Stock-based compensation			2,957	3,016	2,658	2,695	6,178	735
Change in unrealized gain (loss) on investments			(12)	23	1				12
Net loss			(12,875)	(14,449)	(11,917)	(11,161)	(13,406)	(8,591)	(39,241)	(33,158)
Ending balance			$ 45,228	55,224	34,433	51,456	59,916	13,505	$ 45,228	51,456
Ending balance, shares			39,977,654						39,977,654
At-The-Market Sales Agreement [Member]
Issuance of shares including finance costs					455
Underwritten Public Offering [Member]
Issuance of shares upon equity financing/public offering, net				32,222			53,573
Common stock [Member]
Beginning balance			$ 402	$ 361	$ 360	$ 349	$ 274	$ 274	$ 360	$ 274
Beginning balance, shares			39,914,668	35,945,608	35,860,114	34,860,989	27,527,738	27,527,738	35,860,114	27,527,738
Exercise of stock options						$ 2	$ 8
Exercise of stock options, shares			29,537	36,790	25,000	255,394	808,443
Issuance of shares upon exercise/execution of warrants							$ 1
Issuance of shares upon exercise/execution of warrants, shares				44,814		3,385	60,989
Issuance of shares upon Technion settlement							$ 6
Issuance of shares upon Technion settlement, shares							569,395
Repurchase of common shares, shares						5,076	(5,076)
Vesting of restricted stock units			$ 2	$ 3
Vesting of restricted shares, shares			33,449	54,122	25,132
Ending balance			$ 404	$ 402	$ 361	$ 351	$ 349	$ 274	$ 404	$ 351
Ending balance, shares			39,977,654	39,914,668	35,945,608	35,124,844	34,860,989	27,527,738	39,977,654	35,124,844
Common stock [Member] | At-The-Market Sales Agreement [Member]
Issuance of stock, shares					35,362
Issuance of shares including finance costs					$ 1
Common stock [Member] | Underwritten Public Offering [Member]
Issuance of shares upon equity financing/public offering, net				$ 38			$ 60
Issuance of stock, shares	3,833,334	5,899,500		3,833,334			5,899,500
Equity financing issuance costs	$ (200)
Additional Paid-in Capital [Member]
Beginning balance			$ 168,848	$ 133,383	129,825	$ 120,607	$ 60,782	$ 60,047	$ 129,825	$ 60,047
Exercise of stock options			28	90	25	4	89
Issuance of shares upon exercise/execution of warrants				178			51
Issuance of shares upon Technion settlement							(6)
Vesting of restricted stock units				(3)
Equity financing issuance costs			(50)
Issuance of warrants					421
Stock-based compensation			2,957	3,016	2,658	2,695	6,178	735
Ending balance			171,783	168,848	133,383	123,306	120,607	60,782	171,783	123,306
Additional Paid-in Capital [Member] | At-The-Market Sales Agreement [Member]
Issuance of shares including finance costs					454
Additional Paid-in Capital [Member] | Underwritten Public Offering [Member]
Issuance of shares upon equity financing/public offering, net				32,184			53,513
Accumulated Other Comprehensive Income [Member]
Beginning balance			24	1
Change in unrealized gain (loss) on investments			(12)	23	1
Ending balance			12	24	1				12
Accumulated deficit [Member]
Beginning balance			(112,511)	(98,062)	(86,145)	(60,957)	(47,551)	(38,960)	(86,145)	(38,960)
Net loss			(12,875)	(14,449)	(11,917)	(11,161)	(13,406)	(8,591)
Ending balance			(125,386)	(112,511)	(98,062)	(72,118)	(60,957)	$ (47,551)	(125,386)	(72,118)
Treasury stock [Member]
Beginning balance			$ (1,539)	$ (1,250)	$ (1,129)	$ (83)			$ (1,129)
Beginning balance, shares			(128,697)	(101,890)	(91,423)	(8,385)			(91,423)
Issuance of shares upon exercise/execution of warrants				$ (178)			$ (52)
Issuance of shares upon exercise/execution of warrants, shares				(14,893)			(3,385)
Repurchase of common shares							$ (31)
Repurchase of common shares, shares							(5,000)
Vesting of restricted stock units			$ (46)	$ (111)	$ (121)
Vesting of restricted shares, shares			(10,835)	(11,914)	(10,467)
Ending balance			$ (1,585)	$ (1,539)	$ (1,250)	$ (83)	$ (83)		$ (1,585)	$ (83)
Ending balance, shares			(139,532)	(128,697)	(101,890)	(8,385)	(8,385)		(139,532)	(8,385)