Debt - Schedule of Convertible Senior Notes (Details) - Convertible Debt - USD ($)	Sep. 30, 2019	Aug. 31, 2019	Dec. 31, 2018	May 31, 2018
2027 Notes
Liability component:
Principal	$ 1,150,000,000	$ 1,150,000,000.0
Less: debt discount and issuance costs, net of amortization	(229,454,000)
Net carrying amount	920,546,000
Equity component:	220,529,000
2025 Notes
Liability component:
Principal	1,150,000,000		$ 1,150,000,000	$ 1,150,000,000.0
Less: debt discount and issuance costs, net of amortization	(247,098,000)		(275,920,000)
Net carrying amount	902,902,000		874,080,000
Equity component:	$ 285,225,000		$ 285,225,000