Consolidated Statements of Shareholders' Equity (USD $) In Thousands	Share Capital [Member]	Additional Paid-in Capital [Member]	Warrants [Member]	Retained Earnings [Member]	Total
Balance at Dec. 31, 2008	$ 226	$ 754,832	$ 29,884	$ 6,984
Issue of common shares	1,205	2,650
Exercise of warrants (Note 7)		2,777	(2,777)
Exercise of stock options (Note 7)		1,080
Stock-based compensation expense (Note 7)		5,624
Net income				13,941	13,941
Balance at Dec. 31, 2009	1,431	766,963	27,107	20,925	816,426
Issue of common shares	3,366	19,119
Exercise of warrants (Note 7)		24,916	(24,916)
Exercise of stock options (Note 7)		2,300
Stock-based compensation expense (Note 7)		8,483
Net income				37,172	37,172
Balance at Dec. 31, 2010	4,797	821,781	2,191	58,097	886,866
Issue of common shares	2,713	142,109
Exercise of warrants (Note 7)		411	(411)
Exercise of stock options (Note 7)		1,990
Stock-based compensation expense (Note 7)		13,723
Net income				126,917	126,917
Balance at Dec. 31, 2011	$ 7,510	$ 980,014	$ 1,780	$ 185,014	$ 1,174,318