Derivatives and Fair Value Measurements - Summary of Financial Assets and Liabilities (Detail) - Level 2 - Significant Other Observable Inputs - Swaps - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Net Assets (Liabilities)	$ (4,804,000)	$ (5,780,000)
Deferred charges and other assets
Derivatives, Fair Value [Line Items]
Derivative assets	24,000	0
Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	(4,697,000)	(4,457,000)
Other deferred credits and other long-term liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities	$ (131,000)	$ (1,323,000)