Net Income per Share - Schedule of Anti-Dilutive Securities (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from computation	19,729	18,418	17,097
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from computation	9	58	22
Service-based RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from computation	3,258	2,262	660
Performance-based RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from computation	1,054	690	1,007
Convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total shares excluded from computation	7,704	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	7,704	7,704	7,704