Net Income per Share - Schedule of Anti-Dilutive Securities (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from computation	42,002	19,729	18,418
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from computation	0	9	58
Service-based RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from computation	899	3,258	2,262
Performance-based RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from computation	1,509	1,054	690
Convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from computation	19,797	7,704	7,704
Warrants related to issuance of convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from computation	19,797	7,704	7,704