Derivatives and Fair Value Measurements - Swaps in Balance Sheet (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Asset derivatives not designated as hedging instruments	$ 1,119	$ 30
Liability derivatives not designated as hedging instruments	(5,923)	(5,810)
Net total not designated as hedging instruments	(4,804)	(5,780)
Swaps | Deferred charges and other assets
Derivatives, Fair Value [Line Items]
Asset derivatives not designated as hedging instruments	24
Liability derivatives not designated as hedging instruments	0
Net total not designated as hedging instruments	24
Swaps | Other current liabilities
Derivatives, Fair Value [Line Items]
Asset derivatives not designated as hedging instruments	1,038	11
Liability derivatives not designated as hedging instruments	(5,735)	(4,468)
Net total not designated as hedging instruments	(4,697)	(4,457)
Swaps | Other deferred credits and other long-term liabilities
Derivatives, Fair Value [Line Items]
Asset derivatives not designated as hedging instruments	57	19
Liability derivatives not designated as hedging instruments	(188)	(1,342)
Net total not designated as hedging instruments	$ (131)	$ (1,323)