Stock Option Activity (Detail) (USD $)	6 Months Ended
	Sep. 30, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Outstanding Options at Beginning of Period	3,022,592
Number of Shares, Granted	236,989
Number of Shares, Exercised	(70,837)
Number of Shares, Cancelled	(5,000)
Number of Shares, Outstanding Options at End of Period	3,183,744
Number of Shares, Options Exercisable at End of Period	1,230,175
Weighted-Average Exercise Price, Outstanding Options at Beginning of Period	$ 37.83
Weighted-Average Exercise Price, Granted	$ 67.21
Weighted-Average Exercise Price, Exercised	$ 33.19
Weighted-Average Exercise Price, Cancelled	$ 53.22
Weighted-Average Exercise Price, Outstanding Options at End of Period	$ 40.10
Weighted-Average Exercise Price, Options Exercisable at End of Period	$ 30.68
Weighted-Average Exercise Price, Weighted-Average Fair Value of Options Granted during the Period