Fair Value Measurements - Financial Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Aug. 31, 2019	Dec. 31, 2018	Jul. 26, 2018
Carrying Amount
Schedule Of Servicing Assets At Fair Value And Amortized Value [Line Items]
Preferred stock derivative liability	$ 5,247
3.25% Convertible Senior Notes Due 2020
Schedule Of Servicing Assets At Fair Value And Amortized Value [Line Items]
Debt instrument, interest rate	3.25%			3.25%
3.25% Convertible Senior Notes Due 2020 | Carrying Amount
Schedule Of Servicing Assets At Fair Value And Amortized Value [Line Items]
Assets measured at fair value on recurring basis	$ 0		$ 27,974
3.25% Convertible Senior Notes Due 2023
Schedule Of Servicing Assets At Fair Value And Amortized Value [Line Items]
Debt instrument, interest rate	3.25%	3.25%		3.25%
3.25% Convertible Senior Notes Due 2023 | Carrying Amount
Schedule Of Servicing Assets At Fair Value And Amortized Value [Line Items]
Assets measured at fair value on recurring basis	$ 50,753
Level 1
Schedule Of Servicing Assets At Fair Value And Amortized Value [Line Items]
Preferred stock derivative liability	0
Level 1 | 3.25% Convertible Senior Notes Due 2020
Schedule Of Servicing Assets At Fair Value And Amortized Value [Line Items]
Assets measured at fair value on recurring basis	0		0
Level 1 | 3.25% Convertible Senior Notes Due 2023
Schedule Of Servicing Assets At Fair Value And Amortized Value [Line Items]
Assets measured at fair value on recurring basis	0
Level 2
Schedule Of Servicing Assets At Fair Value And Amortized Value [Line Items]
Preferred stock derivative liability	0
Level 2 | 3.25% Convertible Senior Notes Due 2020
Schedule Of Servicing Assets At Fair Value And Amortized Value [Line Items]
Assets measured at fair value on recurring basis	0		0
Level 2 | 3.25% Convertible Senior Notes Due 2023
Schedule Of Servicing Assets At Fair Value And Amortized Value [Line Items]
Assets measured at fair value on recurring basis	0
Level 3
Schedule Of Servicing Assets At Fair Value And Amortized Value [Line Items]
Preferred stock derivative liability	5,247
Level 3 | 3.25% Convertible Senior Notes Due 2020
Schedule Of Servicing Assets At Fair Value And Amortized Value [Line Items]
Assets measured at fair value on recurring basis	0		$ 27,974
Level 3 | 3.25% Convertible Senior Notes Due 2023
Schedule Of Servicing Assets At Fair Value And Amortized Value [Line Items]
Assets measured at fair value on recurring basis	$ 50,753