Estimated Fair Values of Other Financial Instruments (Detail) - USD ($) $ in Thousands		Sep. 30, 2019	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Long-term debt, including current portion, Carrying Amount	[1],[2]	$ 645,099	$ 675,229
Long-term debt, including current portion, Fair Value	[1],[2]	$ 549,465	$ 582,370

[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. See to Note 7.