Derivatives and Fair Value Measurements - Fair Values of Swaps in Condensed Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Asset derivatives not designated as hedging instruments	$ 0	$ 0
Liability derivatives not designated as hedging instruments	(4,887)	(5,425)
Net total not designated as hedging instruments	(4,887)	(5,425)
Swaps [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives not designated as hedging instruments	0	0
Liability derivatives not designated as hedging instruments	(3,425)	(5,062)
Net total not designated as hedging instruments	(3,425)	(5,062)
Swaps [Member] | Other deferred credits [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives not designated as hedging instruments	0	0
Liability derivatives not designated as hedging instruments	(1,462)	(363)
Net total not designated as hedging instruments	$ (1,462)	$ (363)