Fair Value Measurements - Financial Instruments Measured on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Aug. 31, 2017
Fair Value Measurements, Recurring | Redeemable Preferred Stock | Level 1
Schedule Of Servicing Assets At Fair Value And Amortized Value [Line Items]
Derivative liability	$ 0	$ 0
Fair Value Measurements, Recurring | Redeemable Preferred Stock | Level 2
Schedule Of Servicing Assets At Fair Value And Amortized Value [Line Items]
Derivative liability	0	0
Fair Value Measurements, Recurring | Redeemable Preferred Stock | Level 3
Schedule Of Servicing Assets At Fair Value And Amortized Value [Line Items]
Derivative liability	3,164	5,247
Fair Value Measurements, Recurring | Redeemable Preferred Stock | Carrying Amount
Schedule Of Servicing Assets At Fair Value And Amortized Value [Line Items]
Derivative liability	$ 3,164	$ 5,247
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 | Fair Value Measurements, Recurring | Level 1
Schedule Of Servicing Assets At Fair Value And Amortized Value [Line Items]
Notes payable	$ 0	$ 0
3.25% convertible senior notes due 2023 | Fair Value Measurements, Recurring | Level 2
Schedule Of Servicing Assets At Fair Value And Amortized Value [Line Items]
Notes payable	0	0
3.25% convertible senior notes due 2023 | Fair Value Measurements, Recurring | Level 3
Schedule Of Servicing Assets At Fair Value And Amortized Value [Line Items]
Notes payable	42,257	50,753
3.25% convertible senior notes due 2023 | Fair Value Measurements, Recurring | Carrying Amount
Schedule Of Servicing Assets At Fair Value And Amortized Value [Line Items]
Notes payable	$ 42,257	$ 50,753