Notes Payable - 2.25% Convertible Senior Notes Due 2022 - Balances (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Aug. 31, 2019	Aug. 12, 2019	Jun. 30, 2015
Liability component:
Long-term Debt, Gross	$ 550,130
Less: unamortized debt discount	(94,475)
Less: unamortized debt issuance costs	(7,300)
Net carrying amount	418,924
Convertible Senior Notes
Liability component:
Less: unamortized debt discount	(94,475)	$ (104,700)
Less: unamortized debt issuance costs	(7,300)	(8,005)
Net carrying amount	418,924	407,994
Total equity component	112,309	112,309
2.25% Convertible Senior Notes due 2022 | Convertible Senior Notes
Liability component:
Aggregate principal amount of notes issued	120,699	120,699			$ 335,700
Total equity component	19,807	19,807
0.75% Convertible Senior Notes due 2024 | Convertible Senior Notes
Liability component:
Aggregate principal amount of notes issued	200,000	200,000	$ 200,000	$ 200,000
Total equity component	41,152	41,152
1.50% Convertible Senior Notes due 2026 | Convertible Senior Notes
Liability component:
Aggregate principal amount of notes issued	200,000	200,000	$ 200,000	$ 200,000
Total equity component	$ 51,350	$ 51,350