Notes Payable - 2.25% Convertible Senior Notes Due 2022, 0.75% Convertible Senior Notes Due 2024 and 1.50% Convertible Senior Notes Due 2026 (Details) - Convertible Senior Notes - USD ($) $ in Millions	1 Months Ended
	Aug. 31, 2019	Jun. 30, 2015	Mar. 31, 2020
2.25% Convertible Senior Notes due 2022
Debt Instruments [Abstract]
Debt issuance costs incurred		$ 11.7
Debt issuance costs allocated to equity components		4.0
Debt issuance costs allocated to liability components		$ 7.7
Debt instrument term		7 years
Effective interest rate on liability components			9.50%
0.75% Convertible Senior Notes due 2024 and 1.50% Convertible Senior Notes due 2026
Debt Instruments [Abstract]
Debt issuance costs incurred	$ 9.0
Debt issuance costs allocated to equity components	2.1
Debt issuance costs allocated to liability components	$ 6.9
0.75% Convertible Senior Notes due 2024
Debt Instruments [Abstract]
Debt instrument term	5 years
Effective interest rate on liability components			6.10%
1.50% Convertible Senior Notes due 2026
Debt Instruments [Abstract]
Debt instrument term	7 years
Effective interest rate on liability components			6.50%