Estimated Fair Values of Other Financial Instruments (Detail) - USD ($) $ in Thousands		Sep. 30, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Long-term debt, including current portion, Carrying Amount	[1],[2]	$ 583,549	$ 645,721
Long-term debt, including current portion, Fair Value	[1],[2]	$ 461,193	$ 556,187

[1] Carrying amounts include aggregate unamortized debt discount and debt issuance costs.

[2] Includes the 5.75% Convertible Notes accounted for under the fair value option. Refer to Note 7.