Capital Stock (Details 5) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Movement of Shareholders Equity
Balance as at December 31, 2010			$ 158,458
Issuance of common shares for stock options exercised			5,095
Net earnings	1,825	13,302	822	39,883
Adjustment to other equity for employee stock options granted			4,797
Adjustment to other equity for non-employee stock options granted			2,232
Adjustment to capital stock for stock options exercised			2,210
Adjustments To Other Equity For Stock Options Exercised			(2,210)
Adjustments to accumulated other comprehensive income to record unrealized hedging gains			351
Adjustments to accumulated other comprehensive income to record the realization of hedging losses upon settlement			(724)
Adjustments to accumulated other comprehensive income to record the amortization of actuarial loss on defined pension plan	53		107
Unrealized change in market value of available-for-sale investment (note 17(e))			(488)
Tax effect of movement in comprehensive income (note 13(b))	164	0	136	0
Balance as at June 30, 2011	$ 170,786		$ 170,786