Debt - Schedule of Convertible Senior Notes (Details) - Convertible Debt - USD ($)	Mar. 31, 2019	Dec. 31, 2018	May 31, 2018	Feb. 28, 2014
2025 Notes
Liability component:
Principal	$ 1,150,000,000	$ 1,150,000,000	$ 1,150,000,000
Less: debt discount and issuance costs, net of amortization	(266,416,000)	(275,920,000)
Net carrying amount	883,584,000	874,080,000
Equity component:	$ 285,225,000	$ 285,225,000
2019 Notes
Liability component:
Principal				$ 690,000,000