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	Dec. 31, 2018	Jun. 30, 2018	Jan. 18, 2018	Dec. 31, 2017	Dec. 31, 2014
Class of Stock [Line Items]
Unpaid principal balance		$ 786,495			$ 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	$ 221,600
Interest rate percentage				5.00%
Affiliated entity | Convertible Promissory Notes due December 2019 and 2020, Recourse | Convertible promissory notes
Class of Stock [Line Items]
Unpaid principal balance			$ 40,100		$ 38,300
Interest rate percentage						8.00%
Convertible stock price (in dollars per share)	$ 38.64	$ 38.64