Carrying Value of Convertible Senior Notes (Detail) - 2.125% Convertible Senior Notes due 2021 - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Principal amount	$ 114,989	$ 114,989
Unamortized debt discount	(8,840)	(9,781)
Unamortized debt issuance costs	(1,554)	(1,720)
Total convertible senior notes	$ 104,595	$ 103,488

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, 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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