Summary of Significant Accounting Policies (Details) - USD ($)	Jun. 25, 2018	Oct. 10, 2017	Sep. 30, 2018	Dec. 31, 2017	Mar. 31, 2013
Common stock shares authorized			120,000,000	120,000,000
Common stock, par value per share			$ 0.001	$ 0.001	$ 0.001
Temporary equity, shares authorized			10,000,000	10,000,000
Temporary equity, par value per share			$ 0.001	$ 0.001
Net proceeds	$ 162,899
Common stock, outstanding			34,382,525	27,284,140
IPO
Issuance of stock (in shares)	6,591,800
Minimum price per share	$ 26.42
Underwriter option to purchase
Issuance of stock (in shares)	859,800
Gross proceeds	$ 174,155
Common stock | IPO
Issuance of stock (in shares)		8,107,500
Minimum price per share		$ 17.00
Gross proceeds		$ 137,828,000
Net proceeds		$ 125,658,000
Conversion of Series A Convertible Preferred Stock and Series A-1 Junior Preferred Stock into common stock (in shares)		17,406,338
Common stock | Underwriter option to purchase
Issuance of stock (in shares)		1,057,500