Common Stock (Details) (USD $)	12 Months Ended	0 Months Ended		12 Months Ended
	Dec. 31, 2012	Feb. 15, 2008 Employee benefit stock	Dec. 31, 2012 Employee benefit stock	Dec. 31, 2012 Common Stock	Dec. 31, 2012 Stock Options	Dec. 31, 2011 Stock Options	Dec. 31, 2010 Stock Options
Share-based Compensation Arrangement by Share-based Payment Award
Common share purchase right dividend (in shares)		1
Number of common shares each right is entitled to (in shares)		1
Common share purchase right exercise price (in dolalrs per share)			200.00
Stock repurchase program, authorized amount				$ 30,000,000.0
Share repurchase program period in force (in years)				2 years
Stock Repurchased During Period (shares)	888,056
Antidilutive stock options excluded from computation of earnings per share (in shares)					60,400	137,720	98,700