Debt - Zero-Coupon Convertible Senior Notes Due in 2020 - Additional Information (Detail) - Zero-Coupon Convertible Senior Notes due in 2020 [Member] - USD ($) |
3 Months Ended | 9 Months Ended | |
|---|---|---|---|
Sep. 30, 2020 |
Jun. 30, 2020 |
Sep. 30, 2020 |
|
| Debt Instrument [Line Items] | |||
| Debt converted instrument, aggregate principal amount | $ 33,000,000 | $ 67,000,000 | $ 1,000 |
| Debt instrument, shares issued upon conversion | 16.6665 | ||
| Convertible notes, conversion price | $ 60.00 | $ 60.00 | |
| Common Stock [Member] | |||
| Debt Instrument [Line Items] | |||
| Debt instrument, shares issued upon conversion | 600,000 | 1,100,000 | |