Estimated Fair Values of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, carrying value	$ 640,147	$ 570,854	$ 403,463	$ 899,270
Restricted cash and cash equivalents, carrying amount	18,116	21,962
Investments, carrying amount	45,992	139,006
Debt, carrying amount	(102,708)	(93,735)
Derivative contracts, carrying amount	21,434	(5,029)
Cash and cash equivalents, fair value	640,147	570,854
Restricted cash and cash equivalents, fair value	18,116	21,962
Investments, fair value	45,992	139,006
Debt, fair value	(106,324)	(96,187)
Derivative contracts, fair value	$ 21,434	$ (5,029)