Assets and Liabilities Measured at Fair Value (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Financial assets (liabilities), Carrying value
Canadian government securities with maturities greater than 90 days at the date of acquisition	$ 111,542	$ 173,288	[1]
Current and long-term debt	(2,992,567)	(3,059,475)
Financial assets (liabilities):
Canadian government securities with maturities greater than 90 days at the date of acquisition	111,331	173,234
Current and long-term debt	$ (2,951,992)	$ (2,189,858)

[1] Reclassified to conform to current presentation. See Note B for additional information.