Shareholders Equity and Stock Options (Time Based Restricted Stock Awards) (Detail) (USD $)	3 Months Ended	12 Months Ended				3 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Jun. 30, 2012	Dec. 31, 2010 Time Based Restricted Stock [Member]	Dec. 31, 2012 Time Based Restricted Stock [Member]	Dec. 31, 2011 Time Based Restricted Stock [Member]	Dec. 31, 2010 Time Based Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested awards outstanding, beginning balance							86,707	2,500	2,500
Beginning Balance		$ 37.54	$ 36.63	$ 38.40	$ 37.54		$ 44.55	$ 20.01	$ 20.01
Awards granted						0	51,790	84,667
Options granted	$ 41.27	$ 41.27	$ 46.29	$ 24.26			$ 40.99	$ 45.29	$ 0.00
Stock issued						0	(16,620)	0
Options exercised	$ 42.97	$ 42.97	$ 33.61	$ 31.33			$ 41.64	$ 0.00	$ 0.00
Awards forfeited or expired						0	(6,738)	(460)
Options cancelled	$ 43.57	$ 43.57	$ 30.77	$ 38.92			$ 46.21	$ 47.89	$ 0.00
Non-vested awards outstanding, ending balance						2,500	115,139	86,707	2,500
Ending Balance	$ 40.58	$ 40.58	$ 37.54	$ 36.63	$ 37.54	$ 20.01	$ 43.27	$ 44.55	$ 20.01