Contractual interest rate for funds borrowed, under the debt agreement.

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Fair Value Measurements - Narrative (Detail) - USD ($)	Jun. 30, 2019	Mar. 31, 2019	May 31, 2018
Debt Instrument [Line Items]
Unrealized loss position of securities for more than 12 months	$ 0	$ 0
Convertible Debt \| Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Stated interest rate	0.50%		0.50%
Convertible Debt \| Level 2 \| Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Fair value of Notes	$ 480,800,000