Derivative Financial Instruments - Derivative Financial Instruments (Detail) (Derivatives Designated as Hedges [Member], USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Asset derivatives fair value	$ 1,342	$ 1,189
Liability derivatives fair value	59,798	48,101
Accounts receivable-other [Member]
Derivative [Line Items]
Asset derivatives fair value	1,342	1,173
Accounts payable [Member]
Derivative [Line Items]
Liability derivatives fair value	49,965	32,431
Other assets [Member]
Derivative [Line Items]
Asset derivatives fair value		16
Other liabilities [Member]
Derivative [Line Items]
Liability derivatives fair value	$ 9,833	$ 15,670