Carrying Amounts and Estimated Fair Values of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Financial assets (liabilities), Carrying value
Canadian government securities with maturities greater than 90 days at the date of acquisition	$ 115,603	$ 532,093
Current and long-term debt	(2,245,247)	(599,558)
Financial assets (liabilities):
Canadian government securities with maturities greater than 90 days at the date of acquisition	115,802	532,899
Current and long-term debt	$ (2,357,972)	$ (715,208)