Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Assets:
Derivative financial instruments	$ 6,774
Liabilities:
Long-term obligations	1,527,266	$ 1,560,046
Derivative financial instruments		8,455
Significant Other Observable Inputs (Level 2) [Member]
Assets:
Derivative financial instruments	6,774
Liabilities:
Long-term obligations	$ 1,527,266	1,560,046
Derivative financial instruments		$ 8,455