Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock issuance costs			$ 1,746
Common Stock.
Stock issuance costs		$ 11,100
Common Stock. | Follow-on Offering
Stock issuance costs	$ 600
Common Stock. | Public Offering
Stock issuance costs	$ 1,700
Series A-2
Stock issuance costs			1
Series B redeemable convertible
Stock issuance costs			$ 300