Debt - Hedge Transactions (Details) - Convertible Notes $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) $ / shares
2023 Senior Secured Notes
Debt Instrument [Line Items]
Cost of the hedge transaction(s) | $	$ 17,785
Conversion or exchange price (in dollars per share)	$ 44.62
2023 Senior Secured Notes | Hedging of Convertible Debt Instrument
Debt Instrument [Line Items]
Conversion or exchange price (in dollars per share)	$ 62.48
2021 Convertible Senior Notes
Debt Instrument [Line Items]
Cost of the hedge transaction(s) | $	$ 19,545
Conversion or exchange price (in dollars per share)	$ 59.39
2021 Convertible Senior Notes | Hedging of Convertible Debt Instrument
Debt Instrument [Line Items]
Conversion or exchange price (in dollars per share)	$ 83.14
2020 Convertible Senior Notes
Debt Instrument [Line Items]
Cost of the hedge transaction(s) | $	$ 18,113
Conversion or exchange price (in dollars per share)	$ 45.72
2020 Convertible Senior Notes | Hedging of Convertible Debt Instrument
Debt Instrument [Line Items]
Conversion or exchange price (in dollars per share)	$ 61.55