Fair Value Measurements - Narrative (Detail) - Convertible Debt - Convertible Senior Notes Due 2023 - USD ($) $ in Millions	Sep. 30, 2020	May 31, 2018
Debt Instrument [Line Items]
Stated interest rate	0.50%	0.50%
Level 2
Debt Instrument [Line Items]
Fair value of Notes	$ 431.4

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

No definition available.

Name:	us-gaap_LongTermDebtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant