Shareholders Equity and Stock Options (Summary of Activity Under Stock Option Plans) (Detail) (USD $)	3 Months Ended		6 Months Ended	12 Months Ended
	Dec. 31, 2012		Jun. 30, 2012	Dec. 31, 2012		Dec. 31, 2011	Dec. 31, 2010
Options Outstanding
Beginning Balance			2,401,809	2,401,809		2,626,371	2,401,318
Options granted				46,950		131,750	340,150
Options exercised				(614,263)		(329,964)	(30,675)
Options cancelled				(68,549)		(26,348)	(84,422)
Ending Balance	1,765,947		2,401,809	1,765,947		2,401,809	2,626,371
Options exercisable at End of Period	1,274,340			1,274,340		1,609,982	1,674,979
Options vested or expected to vest at December 31, 2012	1,751,199	[1]		1,751,199	[1]
Weighted-Average Exercise Price Per Share
Beginning Balance			$ 37.54	$ 37.54		$ 36.63	$ 38.40
Options granted	$ 41.27			$ 41.27		$ 46.29	$ 24.26
Options exercised	$ 42.97			$ 42.97		$ 33.61	$ 31.33
Options cancelled	$ 43.57			$ 43.57		$ 30.77	$ 38.92
Ending Balance	$ 40.58		$ 37.54	$ 40.58		$ 37.54	$ 36.63
Options exercisable at December 31, 2012	$ 43.61			$ 43.61
Options vested or expected to vest at December 31, 2012	$ 40.64	[1]		$ 40.64	[1]
Weighted-Average Remaining Contractual Life in Years
Begining Balance	1 year 4 months		5 years
Ending Balance	1 year 4 months		5 years
Options exercisable at December 31, 2012	3 years 2 months
Options vested or expected to vest at December 31, 2012	4 years 2 months	[1]
Aggregate Intrinsic Value
Ending Balance	$ 19,557,233		$ 12,195,931	$ 19,557,233
Options exercisable at December 31, 2012	11,230,647			11,230,647
Options vested or expected to vest at December 31, 2012	$ 19,307,435	[1]		$ 19,307,435	[1]

[1] * In addition to the vested options, we expect a portion of the unvested options to vest at some point in the future. Options expected to vest are calculated by applying an estimated forfeiture rate to the unvested options.