Commitments and Contingencies - Series A Convertible Redeemable Preferred Stock Offering (Details) - USD ($)		2 Months Ended	3 Months Ended		9 Months Ended
	Apr. 23, 2018	Jan. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Subsidiary, Sale of Stock [Line Items]
Proceeds from issuance of convertible redeemable preferred stock, net of issuance costs					$ 0	$ 55,290,000
Payment of dividends on Series A Preferred Stock					11,103,000	5,252,000
Gain upon conversion of Series A convertible redeemable preferred stock					74,110,000	0
Series A Convertible Redeemable Preferred Stock
Subsidiary, Sale of Stock [Line Items]
Accretion of redeemable noncontrolling interests and equity			$ 0	$ 83,955,000	61,974,000	185,149,000
Total redeemable noncontrolling interests and equity			$ 0		0		$ 400,276,000
Series A Convertible Redeemable Preferred Stock | Additional paid-in capital
Subsidiary, Sale of Stock [Line Items]
Accretion of redeemable noncontrolling interests and equity					61,974,000
Series A Redeemable Convertible Preferred Stock - Beneficial Conversion Feature
Subsidiary, Sale of Stock [Line Items]
Accretion of redeemable noncontrolling interests and equity					$ (265,368,000)
Series A Redeemable Convertible Preferred Stock - Beneficial Conversion Feature | Additional paid-in capital
Subsidiary, Sale of Stock [Line Items]
Accretion period					1 year
Series A Preferred Stock
Subsidiary, Sale of Stock [Line Items]
Payment of dividends on Series A Preferred Stock					$ 11,103,000	$ 5,175,000
Class A Common Stock
Subsidiary, Sale of Stock [Line Items]
Common stock, par value (in dollars per share)	$ 0.004		$ 0.004		$ 0.004		$ 0.004
Private Placement | Series A Convertible Redeemable Preferred Stock
Subsidiary, Sale of Stock [Line Items]
Sale of stock, number of shares agreed to be issued in transaction (in shares)		400,000
Proceeds from issuance of convertible redeemable preferred stock, net of issuance costs		$ 400,000,000
Number of shares converted (in shares)	36,143,000