Convertible Senior Notes - Schedule of Note Hedges (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	[1]	Dec. 31, 2016	[1]
Debt Instrument [Line Items]
Purchase	$ 0	$ 128,017		$ 0
2022 Note Hedge
Debt Instrument [Line Items]
Note Hedged Shares Of Common Stock Remaining	5,806,936
Purchase	$ 128,017
Shares (in shares)	5,806,936
2018 Note Hedge
Debt Instrument [Line Items]
Note Hedged Shares Of Common Stock Remaining	0
Purchase	$ 135,815
Shares (in shares)	7,783,023

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