Income Taxes (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Schedule of Collaborative Arrangement Agreements [Line Items]
Provision for (benefit from) income taxes	$ 10,341,000	$ 4,337,000	$ (2,318,000)	$ 8,322,000
Excess tax benefits related to stock-based compensation	(5,000,000)		16,800,000
State And Local, Foreign Income Tax, Amount	5,700,000		8,500,000
Tax provision attributable to noncontrolling interest	(400,000)		6,000,000
Unrecognized tax benefits	5,900,000		5,900,000		$ 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	(416,000)	$ 8,132,000	5,989,000	$ 8,523,000
Income tax liability associated with variable interest entity	$ 0		$ 0