Convertible Senior Notes - Summary of Fair Value and Carrying Value of Convertible Senior Notes (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
0.125% Convertible Senior Notes Due 2024 | Fair Value
Debt Instrument [Line Items]
Convertible senior notes	$ 518,787	$ 450,414
0.125% Convertible Senior Notes Due 2024 | Carrying Value
Debt Instrument [Line Items]
Convertible senior notes	355,465	351,058
1.50% Convertible Senior Notes Due 2022 | Fair Value
Debt Instrument [Line Items]
Convertible senior notes	306,360	215,801
1.50% Convertible Senior Notes Due 2022 | Carrying Value
Debt Instrument [Line Items]
Convertible senior notes	$ 80,253	$ 79,224