Assets and Liabilities Measured at Fair Value (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Financial assets (liabilities), Carrying value
Canadian government securities with maturities greater than 90 days at the date of acquisition	$ 173,288	$ 461,313	[1]
Current and long-term debt	(3,059,475)	(2,983,057)	[2]
Financial assets (liabilities):
Canadian government securities with maturities greater than 90 days at the date of acquisition	173,234	462,056
Current and long-term debt	$ (2,189,858)	$ (2,757,671)

[1] Reclassified to conform to current presentation.

[2] Reclassified to current presentation