Organization - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	6 Months Ended
	Mar. 31, 2019	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Date of incorporation		Jun. 08, 2012
Accumulated deficit		$ 278,197		$ 202,553
Proceeds from offering, net of underwriting discounts and commissions and offering expenses		271,224	$ 182,069
Cash, cash equivalents and short and long-term investments		602,400
Follow-On-Offering
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Common stock shares issued	5,663,750
Common stock shares issued, price per share	$ 51.00
Proceeds from offering, net of underwriting discounts and commissions and offering expenses		$ 271,200
Over Allotment Option
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Common stock shares issued	738,750