Convertible Senior Notes - Schedule of Warrants (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) trading_day $ / shares shares	Dec. 31, 2017 USD ($)	[1]	Dec. 31, 2016 USD ($)	[1]	Feb. 01, 2019 shares
Debt Instrument [Line Items]
Proceeds | $	$ 0	$ 54,071		$ 0
Warrant exercise period | trading_day	60
2022 Warrants
Debt Instrument [Line Items]
Proceeds | $	$ 54,071
Shares (in shares)	5,806,936
Strike Price (in USD per share) | $ / shares	$ 203.40
2018 Warrants
Debt Instrument [Line Items]
Proceeds | $	$ 84,525
Shares (in shares)	7,783,023
Strike Price (in USD per share) | $ / shares	$ 107.46
Scenario, Forecast | 2022 Warrants
Debt Instrument [Line Items]
Shares (in shares)						400,000
Scenario, Forecast | 2018 Warrants
Debt Instrument [Line Items]
Shares (in shares)						4,000,000.0

[1] As adjusted to reflect the impact of the full retrospective adoption of Topic 606.