Convertible Senior Notes - Summary of Fair Value and Carrying Value of Convertible Senior Notes (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
0.125% Convertible Senior Notes Due 2024 | Fair Value
Debt Instrument [Line Items]
Convertible senior notes	$ 596,709	$ 450,414
0.125% Convertible Senior Notes Due 2024 | Carrying Value
Debt Instrument [Line Items]
Convertible senior notes	364,451	351,058
1.50% Convertible Senior Notes Due 2022 | Fair Value
Debt Instrument [Line Items]
Convertible senior notes	363,974	215,801
1.50% Convertible Senior Notes Due 2022 | Carrying Value
Debt Instrument [Line Items]
Convertible senior notes	$ 81,464	$ 79,224