Convertible Notes, Convertible Preferred Stock and Common and Preferred Stock Warrants - Convertible Stock and Warrants (Additional Information) (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended
	Jul. 31, 2018	Sep. 30, 2018	Jul. 27, 2018	Jun. 30, 2018	Jan. 18, 2018	Dec. 31, 2017	Dec. 31, 2014
Class of Stock [Line Items]
Unpaid principal balance		$ 792,713				$ 1,008,104
Convertible redeemable preferred stock, shares outstanding (in shares)		0				71,740,162
Class B common stock
Class of Stock [Line Items]
Debt conversion, shares issued (in shares)	5,734,440
Convertible redeemable preferred stock, shares outstanding (in shares)		71,740,162
Convertible Promissory Notes due December 2019 and 2020, Recourse | Convertible promissory notes
Class of Stock [Line Items]
Unpaid principal balance		$ 34,273	$ 221,600
Interest rate percentage		5.00%			5.00%
Affiliated entity | Convertible Promissory Notes due December 2019 and 2020, Recourse | Convertible promissory notes
Class of Stock [Line Items]
Unpaid principal balance				$ 39,900		$ 38,300
Interest rate percentage							8.00%
Convertible stock price (in dollars per share)		$ 38.64	$ 38.64