Indebtedness - Summary of Debt Facilities (Detail) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Nov. 14, 2017
Debt Instrument [Line Items]
Principal amount	$ 820,000,000
Total carrying value of debt facilities	681,900,000	$ 420,554,000
Total fair value of debt facilities	1,391,288,000	952,681,000
2024 Convertible Notes [Member]
Debt Instrument [Line Items]
Principal amount	570,000,000	570,000,000	$ 570,000,000.0
Unamortized discount	(120,182,000)	(140,206,000)
Unamortized discount - debt issuance costs	(7,922,000)	(9,240,000)
Net carrying value	441,896,000	420,554,000
Total fair value of debt facilities	1,141,288,000	$ 952,681,000
2019 Term Loan [Member]
Debt Instrument [Line Items]
Principal amount	250,000,000
Unamortized discount	(9,996,000)
Net carrying value	240,004,000
Total fair value of debt facilities	$ 250,000,000

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

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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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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Carrying value as of the balance sheet date of loans payable (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion.

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