Organization - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended	12 Months Ended
	Jun. 30, 2018	May 31, 2018	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Date of incorporation				Jun. 08, 2012
Accumulated deficit				$ 202,553	$ 134,855
Proceeds from offering, net of underwriting discounts and commissions and offering expenses				181,863	$ 133,862	$ 61,148
Cash, cash equivalents and short and long-term investments				$ 394,800
Follow-On-Offering
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Common stock shares issued		3,750,000
Common stock shares issued, price per share		$ 49.00
Proceeds from offering, net of underwriting discounts and commissions and offering expenses			$ 181,900
Over Allotment Option
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Common stock shares issued	211,147
Common stock shares issued, price per share	$ 49.00		$ 49.00
Proceeds from offering, net of underwriting discounts and commissions and offering expenses			$ 9,700