Statement of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Series E-1 Redeemable Convertible Preferred Stock [Member]
Issuance of redeemable convertible preferred stock, Issuance costs		$ 17
Series F Redeemable Convertible Preferred Stock [Member]
Issuance of redeemable convertible preferred stock, Issuance costs	$ 32	$ 165