Net Income (Loss) Per Share (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Potentially dilutive securities
Total potentially dilutive securities excluded from the computation of diluted weighted average shares outstanding (in shares)	67,926	68,378
Employee stock options
Potentially dilutive securities
Total potentially dilutive securities excluded from the computation of diluted weighted average shares outstanding (in shares)	15,647	24,080
Shares subject to repurchase
Potentially dilutive securities
Total potentially dilutive securities excluded from the computation of diluted weighted average shares outstanding (in shares)	182	32
Time-vesting restricted stock units
Potentially dilutive securities
Total potentially dilutive securities excluded from the computation of diluted weighted average shares outstanding (in shares)	4,945	3,641
Performance-based restricted stock units
Potentially dilutive securities
Total potentially dilutive securities excluded from the computation of diluted weighted average shares outstanding (in shares)	543
Employee Stock Purchase Plan
Potentially dilutive securities
Total potentially dilutive securities excluded from the computation of diluted weighted average shares outstanding (in shares)	105	125
Note Hedge Warrants
Potentially dilutive securities
Total potentially dilutive securities excluded from the computation of diluted weighted average shares outstanding (in shares)	8,318	20,250
2.25% Convertible Senior Notes due 2022
Potentially dilutive securities
Total potentially dilutive securities excluded from the computation of diluted weighted average shares outstanding (in shares)	8,318	20,250
0.75% Convertible Senior Notes due 2024
Potentially dilutive securities
Total potentially dilutive securities excluded from the computation of diluted weighted average shares outstanding (in shares)	14,934
1.50% Convertible Senior Notes due 2026
Potentially dilutive securities
Total potentially dilutive securities excluded from the computation of diluted weighted average shares outstanding (in shares)	14,934