Income Taxes (Recovery) / Expense (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Current expense:
Canada	$ 0	$ 0	$ 0
Foreign	12,393	2,669	1,487
Deferred tax expense:
Canada	0	0	0
Foreign	4,423	8,315	3,990
Income tax expense / (recovery)	$ 16,816	$ 10,984	$ 5,477