Financial Instruments - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Long-term debt, carrying values	$ 1,752,757	$ 1,568,774	$ 1,576,063
Long-term debt, fair values	$ 1,817,950	$ 1,625,193	$ 1,691,478