Financial Instruments - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Fair Value Disclosures [Abstract]
Long-term debt, carrying values	$ 1,846,294	$ 1,686,189	$ 1,752,757
Long-term debt, fair values	$ 1,937,310	$ 1,752,338	$ 1,817,950