Convertible Senior Notes - Schedule of Fair Value (Details) - USD ($)	Jun. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Fair value measurement, debt basis, closing trading price	$ 100	$ 100
Level 2 | 2022 Notes
Debt Instrument [Line Items]
Estimated fair values of notes	796,976,000
Level 2 | 2018 Notes
Debt Instrument [Line Items]
Estimated fair values of notes	$ 833,808,000	$ 681,375,000