Derivatives and Fair Value Measurements - Fair Values of Swaps in Condensed Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Asset derivatives not designated as hedging instruments	$ 133	$ 0
Liability derivatives not designated as hedging instruments	(2,306)	(5,425)
Net total not designated as hedging instruments	(2,173)	(5,425)
Swaps [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives not designated as hedging instruments	105	0
Liability derivatives not designated as hedging instruments	(2,098)	(5,062)
Net total not designated as hedging instruments	(1,993)	(5,062)
Swaps [Member] | Other deferred credits [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives not designated as hedging instruments	28	0
Liability derivatives not designated as hedging instruments	(208)	(363)
Net total not designated as hedging instruments	$ (180)	$ (363)