Long-term Debt - Net Carrying Amount of Liability Component of Convertible Debt (Detail) - 1.75% Convertible Senior Notes due 2021 [Member] - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2016
Debt Instrument [Line Items]
Unamortized issuance cost			$ (5,000)
Debt, Liability Component [Member]
Debt Instrument [Line Items]
Principal	$ 172,500	$ 172,500
Unamortized discount	(17,305)	(23,737)
Unamortized issuance cost	(2,801)	(3,744)
Net carrying amount	$ 152,394	$ 145,019

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Amount, after accumulated amortization, of debt discount.

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

+ References

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
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