Derivative Instruments - Financial Information Related to Cash Flow Hedges (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Derivative [Line Items]
Unrealized losses on hedging transactions, Gross	$ (2,581)	$ 7,355
Unrealized losses on hedging transactions, Income tax expense (benefit)	(599)	2,096
Unrealized losses on hedging transactions, Net	(1,982)	5,259
Cash Flow Hedging [Member]
Derivative [Line Items]
Unrealized losses on hedging transactions, Gross	(9,936)	8,878
Unrealized losses on hedging transactions, Income tax expense (benefit)	(2,695)	2,669
Unrealized losses on hedging transactions, Net	$ (7,241)	$ 6,209