Exchangeable Senior Notes - Additional Information (Detail) - Exchangeable Senior Notes 3.125% due 2035 (the 2015 Notes)	1 Months Ended	3 Months Ended
Sep. 30, 2015 USD ($)	Mar. 31, 2020 day
Debt Instrument [Line Items]
Principal amount of notes issued \| $	$ 575,000,000
Debt stated interest rate		3.125%
Related debt issuance costs \| $	$ 11,992,000
Underwriting fee percentage	2.00%
Amortization period		5 years
Conversion ratio		0.01093
Redemption price as percentage of principal amount of notes plus accrued and unpaid interest		100.00%
Redemption price as percentage of principal amount of notes at request of debt holders and upon occurrence of designated event		100.00%
Notes exchange, threshold percentage		130.00%
Notes exchange, threshold trading days \| day		20
Notes exchange, threshold consecutive trading days \| day		30
Effective interest rate on the liability component		4.00%
Minimum
Debt Instrument [Line Items]
Number of days of written notice to holders of notes required for redemption		30 days
Maximum
Debt Instrument [Line Items]
Number of days of written notice to holders of notes required for redemption		60 days

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Represents the percentage of principal amount used in computation of the redemption price to be paid on conversion of convertible notes at the request of the debt holders and upon the occurrence of a designated event.

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Represents the number of days of written notice to be made to the holders of the notes required for redemption.

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Threshold period of specified consecutive trading days within which common stock price to conversion price of convertible debt instrument must exceed threshold percentage for specified number of trading days to trigger conversion feature.

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Minimum percentage of common stock price to conversion price of convertible debt instruments to determine eligibility of conversion.

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Threshold number of specified trading days that common stock price to conversion price of convertible debt instruments must exceed threshold percentage within a specified consecutive trading period to trigger conversion feature.

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Face (par) amount of debt instrument at time of issuance.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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