Debt (Narrative) (Details) $ in Thousands, CAD in Millions	Dec. 31, 2015 CAD	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Debt [Line Items]
Short-term debt weighted averate interest rate	1.82%	1.82%
Maximum borrowing capacity		$ 312,693	$ 285,000
Committed Revolving Credit Facilities [Member]
Debt [Line Items]
Available borrowing capacity		300,358
Committed Revolving Credit Facilities, Matures May 2018 [Member]
Debt [Line Items]
Maximum borrowing capacity		212,665
Uncommitted Credit Facilities [Member]
Debt [Line Items]
Line of credit facility, current amount | CAD	CAD 60
Available borrowing capacity		170,049
Uncommitted Credit Facilities, Matures November 2017 [Member]
Debt [Line Items]
Maximum borrowing capacity		127,076
Committed Seasonal Bulge Credit Facility [Member]
Debt [Line Items]
Maximum borrowing capacity		$ 50,000