Estimated Fair Values of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, Carrying Value	$ 461,535	$ 640,147	$ 788,965	$ 570,854
Restricted cash and cash equivalents, Carrying Amount	21,942	18,116
Investments, Carrying Amount	18,936	45,992
Debt, Carrying Amount	(101,213)	(102,708)
Forward contracts, Carrying Amount	3,818	21,434
Cash and cash equivalents, Fair Value	461,535	640,147
Restricted cash and cash equivalents, Fair Value	21,942	18,116
Investments, Fair Value	18,936	45,992
Debt, Fair Value	(104,975)	(106,324)
Forward contracts, Fair Value	$ 3,818	$ 21,434