Financial Instruments - Additional Information (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Fair Value Disclosures [Abstract]
Long-term debt, carrying values	$ 1,779,217	$ 1,568,774	$ 1,653,338
Long-term debt, fair values	$ 1,890,319	$ 1,625,193	$ 1,729,511