Stock Incentive Plans (Details 1) (USD $)	1 Months Ended									2 Months Ended					12 Months Ended
	Jul. 31, 2012	Jan. 31, 2012	Dec. 31, 2011	Oct. 31, 2011	Jul. 31, 2011	May 31, 2011	Jan. 31, 2011	Oct. 31, 2010	Feb. 28, 2010	Oct. 31, 2012	May 31, 2012	Apr. 30, 2011	Aug. 31, 2010	Apr. 30, 2010	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Intrinsic value calculated based on grant date fair value
Number of options, granted	7,000	8,500	143,000	75,400	12,500	51,650	26,000	35,000	7,500	36,800	36,750	73,500	145,655	50,671	89,050	382,050	238,826
Intrinsic value calculated based on grant date fair value, Exercise price				$ 10.81			$ 18.80			$ 9.41	$ 9.45	$ 25.61	$ 24.95	$ 19.49
Intrinsic value calculated based on grant date fair value, Exercise price	$ 10.20	$ 9.39	$ 10.19	$ 10.93	$ 16.86	$ 22.92	$ 21.64	$ 22.69	$ 15.00	$ 9.58	$ 10.43	$ 27.63	$ 32.67	$ 20.20
Intrinsic value calculated based on grant date fair value, Intrinsic value per share