Stockholders' Equity (Details Textual)				1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 26, 2019 USD ($) $ / shares shares	Jun. 19, 2019 $ / shares shares	Jun. 18, 2019	Mar. 31, 2013 $ / shares shares	Sep. 30, 2019 $ / shares shares	Sep. 30, 2018 shares	Sep. 30, 2019 USD ($) $ / shares shares	Sep. 30, 2018 shares	Dec. 31, 2017 USD ($) Milestone shares	Dec. 31, 2018 ₪ / shares shares	Dec. 31, 2016 Milestone	Dec. 31, 2014 shares
Class Of Stock [Line Items]
Gross proceeds from offering | $							$ 21,278,000
Common stock, shares issued					15,126,000		15,126,000			10,762,000
Common stock, par value | (per share)					$ 0.001		$ 0.001			₪ 0.07
Antidilutive securities excluded from computation of earnings per share					166,921	98,000	96,615	91,000
Unvested Restricted Ordinary Shares [Member]
Class Of Stock [Line Items]
Antidilutive securities excluded from computation of earnings per share					622,667	622,667	622,667	622,667
Restricted Common Stock [Member]
Class Of Stock [Line Items]
Stock issued during period				2,783,686
Share price of stock issued | $ / shares				$ 0.0068
Shares subject to repurchase option				1,538,353
Share based compensation arrangement by share based payment award period from termination date of employee or consultant for repurchase of shares				2 months
Number of milestones achieved | Milestone									2		2
Common shares, unvested					622,667	622,667	622,667	622,667				769,176
Accelerated ordinary shares vested									146,510
Modification expense resulting from accelerated vesting of ordinary shares | $									$ 1,495,000
Vested After Obtaining Suitable siRNA License [Member] | Restricted Common Stock [Member]
Class Of Stock [Line Items]
Shares vesting percentage				25.00%
Vested After in Vivo Proof-of-concept Achieved [Member] | Restricted Common Stock [Member]
Class Of Stock [Line Items]
Shares vesting percentage				25.00%
Vested After IND Application Completed [Member] | Restricted Common Stock [Member]
Class Of Stock [Line Items]
Shares vesting percentage				25.00%
Vested After in Human Efficacy Achieved [Member] | Restricted Common Stock [Member]
Class Of Stock [Line Items]
Shares vesting percentage				25.00%
Equity Purchase Agreement [Member] | Collaboration Partner - Expanded Ultragenyx [Member]
Class Of Stock [Line Items]
Common stock purchase price per share | $ / shares		$ 10.00
Common stock, shares issued		2,400,000
Common stock, par value | $ / shares		$ 0.001
Purchase of additional shares of common stock		600,000
Purchase of additional shares of common stock price per share | $ / shares		$ 16.00
Equity Purchase Agreement [Member] | Collaboration Partner - Ultragenyx [Member] | Maximum [Member]
Class Of Stock [Line Items]
Ownership interest of common stock		8.00%
Registration Rights Agreement | Collaboration Partner - Ultragenyx [Member]
Class Of Stock [Line Items]
Percentage of minimum common stock may not exercised total shares outstanding			19.99%
Registration Rights Agreement | Collaboration Partner - Ultragenyx [Member] | Maximum [Member]
Class Of Stock [Line Items]
Period to register sale of shares			180 days
H.C. Wainwright & Co., LLC [Member] | Securities Purchase Agreement [Member]
Class Of Stock [Line Items]
Net proceeds from offering after deducting placement agent fees and offering expenses | $	$ 21,300,000
Closing date of offering	Sep. 30, 2019
Common Stock [Member]
Class Of Stock [Line Items]
Stock issued during period					1,995,000		1,995,000
Common Stock [Member] | H.C. Wainwright & Co., LLC [Member] | Letter Agreement [Member]
Class Of Stock [Line Items]
Percentage of cash fee on gross proceeds from offering							6.00%
Common Stock [Member] | H.C. Wainwright & Co., LLC [Member] | Securities Purchase Agreement [Member] | Investor
Class Of Stock [Line Items]
Common stock purchase price per share | $ / shares	$ 11.50
Gross proceeds from offering | $	$ 23,000,000
Common stock, shares issued	1,995,653