Long-Term Debt - Schedule of Interest Expense Related to Long-Term Debt (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Interest Expense, Debt [Abstract]
Contractual interest	$ 2,717	$ 2,662	$ 8,024	$ 7,766
Non-cash expense	1,888	1,746	5,556	4,623
Capitalized interest	(53)		(53)	(61)
Total	$ 4,552	$ 4,408	$ 13,527	$ 12,328