Estimated Fair Values of Other Financial Instruments (Detail) - USD ($) $ in Thousands		Mar. 31, 2016	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Long-term debt, including current portion, Carrying Amount	[1]	$ 1,443,245	$ 1,449,392
Long-term debt, including current portion, Fair Value	[1]	$ 1,291,924	$ 1,240,244

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