Income Taxes (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Schedule of Collaborative Arrangement Agreements [Line Items]
Provision for (benefit from) income taxes	$ 8,055,000	$ (125,903,000)	$ 5,737,000	$ (117,581,000)
Excess tax benefits related to stock-based compensation	(3,100,000)		13,700,000
State and foreign income tax	4,900,000		13,400,000
Tax provision attributable to noncontrolling interest			6,100,000
Unrecognized tax benefits	6,800,000		6,800,000		$ 3,800,000
Income taxes, interest and penalties accrued	0		0
Increase in unrecognized tax benefits is reasonably possible	0		0
Income taxes, material interest or penalties related to uncertain tax positions			0		0
Deferred tax asset subject to valuation allowance					$ 1,600,000,000
Deferred tax assets, valuation allowance	204,700,000		204,700,000
Variable Interest Entity, Primary Beneficiary
Schedule of Collaborative Arrangement Agreements [Line Items]
Provision for (benefit from) income taxes	79,000	$ (120,181,000)	6,068,000	$ (111,658,000)
Income tax liability associated with variable interest entity	$ 0		$ 0