Stockholders' Equity (Deficit) - June 2017 Private Placement (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2018	Dec. 31, 2017
Stockholders' Equity (Deficit)
Value of shares sold by the entity			$ 173,805
Net proceeds after deducting commissions and other transactions costs		$ 311,825	$ 173,805
Private Placement Offering | Purchase Agreement
Stockholders' Equity (Deficit)
Value of shares sold by the entity	$ 35,000
Net proceeds after deducting commissions and other transactions costs	$ 34,900
Private Placement Offering | Common stock | Purchase Agreement
Stockholders' Equity (Deficit)
Number of shares sold by the entity	328,300
Issue price of stock	$ 15.23
Private Placement Offering | Series A Convertible Preferred Stock | Purchase Agreement
Stockholders' Equity (Deficit)
Number of shares sold by the entity	1,969,797
Issue price of stock	$ 15.23